Astronomy

Do celestial objects need to be big to have liquid water on their surfaces?

Do celestial objects need to be big to have liquid water on their surfaces?



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I mean no asteroid, planetoid that I am aware of has water on its surface. It is way more common to see ice in it. So I figured that the size of the celestial body has something to do with the cycle of water. Does this theory hold true? Do exoplanets with water have to be similar size than Earth? To have water does it has to be a rocky planet?

I mean some moons have water inside their crust (I think). Some planets seem to have had water before, like Mars.


Liquid water can't exist in a vacuum. If there is no pressure, then the boiling point will drop to the freezing point and so there will either be ice or water vapour.

And if the world is "small" then its gravity won't hold on to any water vapour, and it will be lost to space. The Earth can have liquid water because its gravity is strong enough to hold onto water vapour, and provide vapour pressure to raise the boiling point to 100 degrees, which is hotter than the temperature due to the sun.

A small world can have a sub-surface water layer, as the ice above it will stop the water from boiling off into space. Enceladus has such a layer, but if Enceladus was a moon of the Earth, the sun would have melted the ice and the water would have boiled off long ago.


Do celestial objects need to be big to have liquid water on their surfaces?

Yes.

In a nutshell: liquid surface water needs an atmosphere. To sustain an atmosphere, a planet must be sufficiently massive, therefore sufficiently large. The warmer a planet, the more mass it needs to sustain an atmosphere. A planet warm enough for liquid water must thus also be large enough to sustain the atmosphere for this liquid surface water to survive.


Liquid water can only exist if pressure is larger than 612 Pa. The boiling point depends on the pressure. At a pressure of 101 kPa, like average conditions on Earth sea level, the boiling point is 373 K (100 °C). At a pressure of 34 kPa (average on the summit of Sagarmatha/Mount Everest), the boiling point is 71 °C:

Source: Cmglee, Wikimedia Commons

For liquid water to exist at the surface, a sufficiently thick atmosphere must exist to provide this pressure. It could be a little thinner than on Earth, but if it's too thin then water might boil all too easily.

Mars has an average surface pressure of 636 Pa on average, which means that in theory, liquid water could barely exist, but only when the temperature is pretty much exactly 273 K (0 °C). One degree colder and it will freeze, one degree warmer and it will boil. In reality surface temperature on Mars is on average 210 K. The pressure on Mars depends on the location, but for future Mars colonists, it should be fun challenge to try to see how long they can make liquid water survive (heated, but unpressurised) at some of its lowest points!

To retain an atmosphere, a planet must have sufficient gravity. If there is not enough gravity, most of the atmosphere will drift off into space due to thermal effects (molecular thermal velocity in excess of escape velocity, see below), solar wind escape (charged particles pushing against the atmosphere), and other (smaller) effects. Worse, not only is most of the atmosphere lost if a planet is too small, but the lighter species such as water are lost more easily than, say, carbon dioxide. So not only must gravity be sufficient to hold onto an atmosphere, it must be sufficient to hold onto water specifically. The only way to counter or prevent losses to space are sufficient gravity (reducing loss) or a constant new supply. The size a planet needs to have to retain an atmosphere depends on temperature:

Source: Cmglee, Wikimedia Commons

To have sufficient gravity, a planet must have sufficient mass. To have sufficient mass, it must be sufficiently large. How large is "sufficiently large"? That depends on the temperature. Titan is quite small, but also very cold. At temperatures warm enough to sustain water, a planet could be a little smaller than Earth, but not much. Mars is too small. Although a Mars-sized planet at an Earth-like temperature could theoretically retain a Titan-like atmosphere of mostly nitrogen for a while (it'd be close, being a bit larger would be safer), it would still lose its water over time.

To have a constant new supply, a planet or moon would need vulcanism. To sustain vulcanism, a planet needs an internal heat supply, for which it also needs sufficient mass, at least to sustain this long term. A moon can also get energy from a planet to sustain volcanism. Maybe a warmer hybrid between heavily volcanic Io and Enceladus with cryovolcanoes around a hypothetical extrasolar planet could sustain a highly dynamic atmosphere, even if it would normally be too small according to the diagram above. That might be unlikely, though; in case of Io, the same energy source that powers the volcanism also strips away the atmosphere (and Io has the least water of anywhere in the solar system). In any case, the only moon with a significant atmosphere in our solar system is Titan, which is also the smallest body in the solar system with an atmosphere. It's very cold at 94 K; if it were warm enough to contain liquid water, it would lose its atmosphere.

Maybe a very young planet could be quite small, still vulcanically active, and still keep on to enough atmosphere to allow for widespread liquid surface water. There are no such planets in the solar system either, but it could be conceivable for an extrasolar planet. For any planet of significant age, however, only mass, thus only size, will help.

Size does matter.


gerrit's answer has done an excellent job of showing that (1) there are a narrow set of temperatures and pressures where liquid water exists and (2) a planet has to be pretty big to have enough gravity to keep water in the atmosphere. However, I wanted to mention this:

However, the conditions required for liquid water can be extended by mixing it with other chemical species.

Salt is often poured onto roads in the winter to melt ice, which is effective because salt water has a lower freezing point and higher boiling point (and is more thermodynamically stable) than pure liquid water. For instance, sea water freezes at 271 K (28 °F), which is lower than the freezing point of pure water, 273 K (32 °F). Coolant in cars usually contains water with ethylene glycol added to depress the freezing point and elevate the boiling point.

This figure from Cynn et al. shows that a mixture of 63% water plus 37% ammonia allows liquid water to exist down to 180 K, although it's hard to tell where the pressure cutoff might be at this temperature from this graph. The pressure cutoff goes down temperature, so it's certainly below 100 kPa. You might be able to sustain liquid water-ammonia mixtures at low temperatures and pressures on the surface of Mars-sized bodies or smaller.

Water-ammonia mixtures are thought to be present beneath the surface of many bodies in the outer solar system, including Titan, Pluto, Charon, and Ganymede. Cryovolcanism based on eruptions of liquid ammonia-water mixtures may be more common than not among the terrestrial satellites beyond Mars.


Why Is Earth The Only Planet Capable Of Sustaining Life Known So Far?

If we want to be really accurate, it is good to say that the Earth can sustain life today. There have been periods when it was not, and there will be periods when it will not be. Our scientific knowledge accumulated until now also allows us to understand why life came about and managed to remain here… And if we apply these reasons to other well-known celestial bodies, we begin to see them with different eyes.

  • We need a star to warm the planet or moon. Okay, we have the sun.
  • We need organic molecules. Okay, we have this here in abundance too.
  • We need an atmosphere that is dense enough. No problem!
  • Do we need oxygen? Not necessarily. Several terrestrial bacteria die from contact with oxygen. Plant ancestors also had to deal with this since before the plants themselves there was not so much oxygen in the air.
  • We need protection against space radiation. Here on Earth, we have the magnetic field, so everything is in order.
  • We need liquid water. Here we have it in abundance too.

So, where could we f ind life beyond here? Studying our solar system, we found some interesting candidates. They are:

The Jupiterian moon Europa…

The Jupiterian moon Ganymede…

The Saturnian moon Enceladus, and…

What do these places all have in common that made them candidates for life? Mars is cold, as far as possible to sustain life… The three moons, then, are much more distant from the sun. Organic molecules, ok… They have already been found on Mars and Enceladus. Dense atmosphere? We don’t have in any of the objects in question, neither oxygen in large quantities. We don’t have magnetic protection on any of them either. Water in liquid state… WE HAVE! In the three moons, in huge quantities! We have a lot of ice on Mars, and an underground lake of some size was discovered a few years ago. But what would life be like in these places?

This is a hydrothermal vent. They are small cracks at the bottom of an Earth’s ocean that eject water heated by the lava below them. Various researches have found that there are all the elements necessary to create life in these fissures, and in many of them, microorganisms and small animals living there have been discovered, completely isolated from the sun and surface oxygen.

This kind of life could exist in the three mentioned moons! They all have a lot of water under a thick layer of ice. This means that this ice assumes our magnetosphere's role, protecting what is under from the radiation. The fact that the three moons are close to gaseous giant planets indicates that they suffer a very strong “tidal effect” (that is why you see “cracks” on their surfaces), and as this one comes and goes, heats the water and the core of these moons, it is very likely that there are cracks similar to the one in the photo above, perhaps much larger.

Mars, from what we observed, must have harbored life in the distant past. There is evidence of rivers and seas across the planet. The underground lake can maintain some kind of life from this past, adapted to the new conditions.
So it is quite possible that, in the coming years, we will find evidence of life in some or all of these places. Microscopic life, very likely. Animal and plant life? It is possible in the three moons. Intelligent life? Unlikely. But there must be life out there, in our solar system! And this means that if we find planets or moons with similar conditions, life must also have appeared in the orbit of other stars!

Up to July 2020, four thousand, two hundred and eighty-one exoplanets have been found. Several of them are in the so-called “habitable zone” of their stars, orbits where the heat can keep liquid water. If even here, in more adverse conditions, we are likely to find life, what about a planet with liquid water on the surface?

The universe is too big… If there is only life here… It would be a huge waste of places!

(“Contact” reference intended)

ADDENDUM: Today, September 14, 2020, the presence of phosphine in the Venusian atmosphere was announced. Phosphine is one of the by-products of the metabolism of anaerobic beings here on Earth. They have already found phosphine in Jupiter and Saturn, but there the conditions of pressure and heat, much greater than those of Venus, may have created the compound. On Venus, the most likely answer, as far as we know, is the presence of life, possibly anaerobic microscopic life. It is still early to reach conclusions much research needs to be done, after all, it is an alien world, and some unusual chemical reactions on Earth can frequently happen there, creating phosphine without the need for living beings. But the announcement is exciting. It can mean that life is much more versatile than we imagined. If so… We must be surrounded by life throughout the Solar System!

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Are there oceans on other planets?

Europa is thought to have subsurface liquid water. Scientists hypothesize that Europa's hidden ocean is salty, tidal, and causes its ice surface to move, resulting in large fractures which are clearly visible in the above image. Although Europa is thought to have the ingredients needed to support life &mdash water, energy, organic compounds &mdash it lies outside of our solar system's habitable zone. (Image Credit: NASA/JPL/Ted Stryk).

Currently, Earth is the only known planet (or moon) to have consistent, stable bodies of liquid water on its surface. In our solar system, Earth orbits around the sun in an area called the habitable zone. The temperature, along with an ample amount of atmospheric pressure within this zone, allows water to be liquid for long periods of time.

Evidence points to water on other planets in our solar system. In 2015, NASA confirmed that liquid water flows intermittently on present-day Mars. Also in 2015, scientists used data from NASA's Cassini mission to discover that a global ocean lies beneath the icy crust of Saturn's moon Enceladus. Scientists believe that Jupiter's moon Europa has a subsurface ocean as well.


Breakthrough Listen releases catalog of "Exotica" – objects of interest as "technosignatures"

Credit: CC0 Public Domain

Breakthrough Listen, the initiative to find signs of intelligent life in the universe, today released an innovative catalog of "Exotica"—a diverse list of objects of potential interest to astronomers searching for technosignatures (indicators of technology developed by extraterrestrial intelligence). The catalog is a collection of over 700 distinct targets intended to include "one of everything" in the observed universe—ranging from comets to galaxies, from mundane objects to the most rare and violent celestial phenomena.

The comprehensive new catalog is the first in recent times that aims to span the entire breadth of astrophysical phenomena, from distant galaxies to objects in our own solar system. The Listen team developed it conceptually, compiled it and shared it with the astronomical community in the hope that it can guide future surveys—studying life beyond Earth and/or natural astrophysics—and serve as a general reference guide for the field.

"Many discoveries in astronomy were not planned," said the lead author of the new catalog, Dr. Brian Lacki. "Sometimes, a major new discovery was missed when nobody was looking in the right place, because they believed nothing could be found there. This happened with exoplanets, which might have been detected before the 1990s if astronomers looked for solar systems very different than ours. Are we looking in the wrong places for technosignatures? The Exotica catalog will help us answer that question."

"The catalog is not just limited to SETI, though," noted Lacki. "My hope is that any program with a new capability may use the Exotica catalog as a shakedown cruise around the universe."

The Exotica catalog contains four categories of object:

  1. Prototypes: a list containing at least one example of every known kind of celestial object (apart from those too transient to present realistic observation targets). Planets and moons, stars at every point of their life cycle, galaxies big and small, serene star clusters and blazing quasars, and more are all included in the list.
  2. Superlatives: objects with the most extreme properties. These include examples like the hottest planet, stars with unusually high or low metal content, the most distant quasar and fastest-spinning pulsar, and the densest galaxy.
  3. Anomalies: enigmatic targets whose behavior is currently not satisfactorily explained. For instance, the famous "Tabby's Star" with its bizarre dimming behavior "Oumuamua—the interstellar object that passed near Earth in 2017 unexplained optical pulses that last mere nanoseconds and stars with excess infrared radiation that could conceivably be explained as waste heat from alien megastructures.
  4. A Control sample of sources not expected to produce positive results.

Accompanying the catalog is extensive discussion of classification of objects and a new classification system for anomalies, as well as plans for upcoming and potential observations based on this work.

The search for extraterrestrial intelligence (SETI) has been pursued as a serious scientific program, though at times sporadically, for 60 years. In the last five years, Listen has massively increased the scope of radio (as well as optical) searches, and has developed technology, deployed at giant radio telescopes on three continents, that enables coverage of an unprecedented range of frequencies at high resolution. Most recently, Listen observed the Kepler 160 system, searching for signals from an Earthlike planet (found earlier this month) around a Sunlike star.

Dr. Andrew Siemion, leader of the Breakthrough Listen science team at the University of California, Berkeley's SETI Research Center (BSRC), said, "Technosignature searches to date have largely focused on the search for 'life as we know it': nearby stars—in particular those known to host planets with the potential for liquid water on their surfaces. The expanded search capabilities that Breakthrough Listen has made possible allow us to consider a much wider range of possible technology-laden environments."

As yet, however, no confirmed technosignature has been detected from any of the objects targeted by SETI searches. One explanation is, of course, that we are alone in the universe. On the other hand, in a vast cosmos it is certainly possible that astronomers have yet to look in the most promising places. The new Exotica catalog is the centerpiece of Listen's efforts to expand the diversity of targets. The crucial principle behind it is the concept of "survey breadth," i.e., the diversity of objects observed during a program. This should help astronomers constrain the range of potential habitats for extraterrestrial intelligence, as well as rule out the possibility that any phenomena widely considered natural are in fact artificial. Conversely, it may identify natural events, or confounding data such as interference, that mimic the kinds of artificial signal SETI researchers are on the lookout for.

"Breakthrough Listen has already greatly expanded the breadth and depth of its search. The publication of this catalog is a new and significant step for the program," said Yuri Milner, the founder of the Breakthrough Initiatives.

"When it comes to the search for intelligent life, it's vital to have an open mind," noted S. Pete Worden, executive director of the Breakthrough Initiatives. "Until we understand more about the forms another civilization and its technology could take, we should investigate all plausible targets. Cataloging them is the first step toward that goal."


Mythology

In astrology, which is not a science, Aquarius is the 11th sign in the Zodiac and represents those born between Jan. 20 and Feb. 18.

The Greeks linked this constellation with Ganymede, the cup bearer to the gods. According to lore, Ganymede was a good-looking young man who was the object of Zeus' affection and was brought to Mount Olympus, where he served as cup bearer to the gods and was granted eternal youth.

Aquarius has also has various meanings and associations in other cultures. Babylonian astronomers identified the constellation as representing the god Ea, or "The Great One," which was often pictured with an overflowing vessel. In ancient Egypt, the water bearer&rsquos jar was said to cause the spring overflow of the Nile when it was dipped into the river. The Chinese astronomers viewed the "stream" as soldiers.


Formation of the Solar System

The current configuration and characteristics of the solar system should provide us with some clues as to how it formed. If you are going to try to understand the processes that went into the formation of the solar system and are attempting to theoretically duplicate it, then you better make sure your model duplicates these characteristics and others that are important aspects of the solar system. It may also be the case that there were rare events in the formation of the planets in our solar system that we don't expect to occur in other planetary systems. Of course, there is also the question of how likely is it that a planetary system forms around a star - so many questions, so little time!

Here are some of the features of the solar system, which can be thought of as clues to how the solar system formed.

  • Most of the material in the solar system is in the Sun (actually, about 99.9 % of it is). The planets and all the other junk are pretty minute in comparison to the Sun.
  • All the planets orbit the Sun in about the same orbital plane, the ecliptic (Mercury deviates from this the most with a 7 degree tilt).
  • The planets orbit the Sun in the same direction, counter-clockwise as viewed from above the north pole.
  • The planets' orbits are very close to being circular (Mercury is the least circular with an eccentricity of 0.21).
  • Most planets rotate on their axes in the same direction. The exceptions for this are Venus and Uranus. Venus is completely tipped over, while Uranus is sort of on its side.
  • The planets' satellites tend to follow the motions of the planets they are orbiting and rotating in a counter-clockwise direction. There are actually many exceptions to this rule, but most do follow it fairly well.
  • The density of the planets decrease with increasing distance from the Sun. This also indicates that the compositions of the planets change with increasing distance from the Sun. When you include things like asteroids, their compositions also follow this trend.
  • The outer planets are more massive than the inner planets and are made mainly of hydrogen and helium.
  • There is extensive cratering of both planets and satellites, and it is thought that most of this cratering occurred at about the same time.

How is a solar system made? What are the ingredients that we need to make one? Actually, you could answer these questions by asking how the Sun was made since it is the main component of the solar system. Remember, it has most of the mass of the solar system. If someone were to do a survey of our solar system, they'd most likely say that there is a G2 Main Sequence star in it and not much else. Maybe they'd also mention Jupiter, but beyond that, everything else is pretty minuscule. If you are going to make a solar system, you are going to primarily be involved in making a star (the Sun in this case). We have already gone over this process of how stars form, but we did not look at how the other stuff - planets, satellites, etc. form since they are such small components of the whole process.

To make a solar system you need to start out with a gas and dust cloud composed of about 70% hydrogen, 27% helium, and 3% all else. We're talking about a gas cloud that will form into the solar system, so we usually refer to it as the solar nebula . Now you know where all of this stuff has come from, don't you? At least, if you have been paying attention the past 11 weeks or so, you should know. First of all, hydrogen and helium are the most abundant elements in the Universe and were formed in the Big Bang (even though some He is formed in other stars, that doesn't contribute a lot to the overall abundance). All of the other stuff (the stuff that makes up 3% of the mass) came from secondary sources, through the fusion of elements in the cores of stars. These stars then spew this material out through various mechanisms such as stellar winds, planetary nebula phases, and the ultimate littering of the galaxy, supernova explosions. The most common elements found in this 3% are things like oxygen, carbon, nitrogen, silicon, iron, and so forth.

You have a solar nebula sitting out there that will start collapsing down to make the Sun and some other stuff. We don't want it to form in any general way, do we? We have to have it ending up as a solar system like we see today, with all the planets spread out around the Sun in the ecliptic. How can we do that? One thing that will help the process is to have the nebula rotating a little bit. What good is that? This has to do with that concept of angular momentum that we have run into before (see the stuff about pulsars). As something collapses, it spins faster. The gas cloud starts collapsing, with most of the stuff collapsing into where the Sun will be. Does that mean there will only be a Sun formed in the middle? No, that's not what's going to happen. If you have something spinning really fast, there is a tendency for it to stretch out. Have you ever seen a person make a "real" pizza? I don't mean someone taking a pizza out of a freezer and putting it into a oven, I mean someone making a pizza the old fashioned way. One thing they do is toss the dough up into the air. Is that all they do? No, they also spin it. Why? The rotation (angular momentum) helps to spread out the material (dough). The collapse speeds up the rotation, which in turn spreads stuff out into a flat disk (like a pizza or a solar system). This explains why all of the planets and most of the material in the solar system are found in this disk (the ecliptic) and are moving around the center in the same direction.

Now that you have all of the stuff in a nice, neat, flat disk, you can start making planets - well, not right away. Material will first come together in little bits and some bits will come together more easily than others. Why? The temperature of the disk will play a role into how quickly things form into bigger chunks of material and if it is even possible for some things to form. Near the Sun it is very difficult for the lightweight gases and ices to come together since the strong radiation from the newly forming Sun will tend to break these things up easily. Only stuff with strong gravitational attraction (heavy stuff) will be able to come together and stay together. This would include the heavy elements or what you might think of as the stuff that makes up rocks and metals. You have to remember, this high density stuff is sort of rare in the solar nebula compared to the lightweight stuff, so you aren't going to be making many of these rocky/metallic chunks or very large chunks of rocky/metallic material. Further from the Sun, the temperature of the cloud is cooler and gases and ices can coalesce easily - as well as the less common metals and silicates. There are more of the light weight (low density) elements, so they will far outnumber the heavier metals and rocks. You can see right away that the densities of the planets vary according to the heat (distances) from the newly forming Sun. The sizes of the planets are influenced in a similar way since the inner planets are made up of the less abundant heavy elements, they will end up having lower masses, while the outer planets are made up of the most common materials, hydrogen and helium, and therefore they will be much bigger. Another aspect of this temperature dependency on the formation of the planets is the size of Jupiter. Jupiter is located closer to the Sun than the other Jovians and is about as close as a Jovian type planet can get - it is also the most massive. When Jupiter formed it sort of gathered up most of the available mass, since it was close to the location where all the abundant lightweight stuff was able the coalesce. It is closest Jovian to the Sun, so it is closer to where more of the mass is. The end result is that Jupiter is by far the most massive planet in the solar system.

Let's get back to making planets. What is driving the whole solar system formation process? Gravity is the force behind it all (as you should know by now, "Gravity Rules!"). The material is coming together, forming larger and larger chunks. Condensation and accretion will cause concentrations to develop in the solar nebula until the chunks reach sizes where they dominate their areas - they are now planetismals . These are the basic building blocks for a planet. They vary in sizes from tiny fractions of a centimeter to several kilometers. They are just basically big enough (and therefore have enough gravity) to pull in more material so that they can get bigger. Of course, if you combine enough of these planetismals together you will make your basic planet.

Figure 4. A planet that comes together gradually will have a mish-mash composition. Once it gets heated up, the layers will sort themselves out, with the high density stuff sinking to the middle and the low density stuff rising to the surface.

Now the planets that you make will depend upon what material is in the area. The inner solar system is full of rocky and metallic planetismals, while the outer solar system is dominated by gaseous and icy planetismals. The material comes together and makes bigger and bigger chunks. Now you have a great big glob of different planetismals - so why don't planets look like big mixed up globs of material? As these things come together and make up the planets, there is a lot of heat released by radioactive elements (I'll talk more about this stuff later), and this helps to heat up the interiors of the planets. When the rocks, gases and metals are heated and become sort of squishy they rearrange themselves, so that the high density stuff (the metals) sink to the center and the lower density stuff (the gases) rise to the surface. This is just like how some salad dressings separate their material - high density stuff sinks, low density stuff floats. To be really technical, we can say that the planet becomes differentiated once the stuff gets sorted out. That just means that the different elements get arranged according to density - high density in the center, low density on the surface.

While the planets were forming, some of the big ones, like the Jovians, may have done the same thing that the solar nebula did. By spinning fast, the clouds of material that would become something like Jupiter would form into a disk and then parts of the disk could form into small objects like moons. The big Jovian planets can be thought of as mini-solar systems as they make their satellites. They have so much mass that it is easy for them to form satellites. It is also possible that they can catch stray satellites - objects that formed elsewhere but get too close to the Jovians so they are trapped by their strong gravity into an orbit.

As planets (and satellites) start to take shape and their surfaces start to solidify, they will experience a rather nasty episode of the solar system cleaning up. During the first 500 million years of the solar system's history, there would have been a lot of big planetismals floating around that weren't incorporated into planets. When the planets and their moons had pretty much formed, these miscellaneous planetismals would have slammed into them. The earliest part of the solar system's history would have involved a lot of damage to the planets and satellites. This era is generally referred to as the Heavy Bombardment era. This would have been the time that the really big craters currently seen on the Moon and Mercury were made. It should be remembered that all planets, satellites, asteroids and other objects were hit by these planetismals at this time as well, but in many cases these impact craters were covered up or erased. The most intense part of the heavy bombardment era is thought to have occurred around 3.8-4.1 billion years ago. By this time the modern structures and physical characteristics of the planets were pretty well established and they ended up as targets of big planetismals. I should also mention that we think the formation of the solar system probably started around 4.6 billion years ago - this is a number that most astronomers and geologists are pretty happy with (I'll explain why in a little while).

Another cleaning up process involved the Sun. While planets and planetismals were doing their thing, there would still have been some stuff floating around that wasn't really part of a planet, or perhaps it was material that was ejected by a planet. This would have included a lot of hydrogen and helium that couldn't be parts of the terrestrial planets since they were too hot to hold onto them. Most of these light gases in the inner solar system were cleared out due to the strong solar wind as the Sun became a true star. The outer planets, however, are far enough away from the Sun that the solar winds didn't do much damage. Also, because the Jovian planets are so huge, they are able to hold onto their outer layers better (more mass, more gravity).

Figure 5. The various steps in the formation of the solar system. Top left - Gas and dust cloud - the solar nebula starts to contract. Top center - The protosun starts to form, pulling in most of the mass. The rotation of the disk increases due to angular momentum. Top right - The disk forms around the protosun, which is getting hotter and hotter due to contraction. Bottom left - The temperature of the Sun reaches a point where it will influence the area around it and start to blow the lightweight material from the inner solar system, leaving behind only the heavier dust and metals (mainly). Bottom center - The largest planetismals in the various locations will start to pull in more material, clearing out the areas around them. Bottom right - Eventually everything comes together to make the solar system we see today.

It appears from our analysis of this process that it seems to have occurred rather quickly, on the order of a few hundred million years. We also have some hints about this process by looking at other young star systems. If you go back to the star formation part of the course you might remember that we often see disks of material around young stars. These disks could be indicators of the start of the planetary system formation process. The disks are pretty big, so it isn't too difficult to see them, especially with techniques that let us block out the light from the star or viewing them with infrared telescopes. Quite a few stars have been found with some very tantalizing looking disks. Many have been observed with infrared telescopes like IRAS and Spitzer, while in some cases they can be seen with the Hubble Space Telescope. In some cases it appears that similar things like asteroid belts are also seen around other stars, as can be seen here. It also appears that the formation of planets can also lead to their destruction, which is the case seen here. A recent observation by the infrared Herschel telescope has revealed a water vapor rich disk of material around a star that is in the process of forming. Of course some of this water will form into icy objects, some will stay in a gas form and some can become liquid water - that will depend upon where in the disk the material is located.

Some recent observations of young stars find evidence of planet formation, in these cases around stars that are only a few million years old. The planets that appear to have formed would be the jovian types, which makes sense due to their large mass and gravitational pull. Also, observations of very small stars (brown dwarfs) appear to also show indications of the planet formation process, with dusty disks of material surrounding them. As more data comes in, we find that the process of solar system formation is pretty widespread and in some cases, fairly easy to do.

Figure 6. (click on to see larger image) Some examples of disks or rings of material around some stars, as seen by the Hubble Space Telescope. In both pictures, the light from the star is blocked out so that the dusty disk is easier to see - the blocked area is indicated by the large circle, while the star itself is pretty small. A scale for comparison is provided so that you can see how these systems compare to our solar system. Notice how the rings look sort of like the drawings in Figure 5! AU Microscopii Image Credit: NASA, ESA, J.E. Krist (STScI/JPL), D.R. Ardila (JHU), D.A. Golimowski (JHU), M. Clampin (NASA/GSFC), H.C. Ford (JHU), G.D. Illingworth (UCO-Lick), G.F. Hartig (STScI) and the ACS Science Team. HD 107146 Image Credit: NASA, ESA, D.R. Ardila (JHU), D.A. Golimowski (JHU), J.E. Krist (STScI/JPL), M. Clampin (NASA/GSFC), J.P. Williams (UH/IfA), J.P. Blakeslee (JHU), H.C. Ford (JHU), G.F. Hartig (STScI), G.D. Illingworth (UCO-Lick) and the ACS Science Team.

Now you are probably wondering how we know when all of this stuff happened. It's due to the presence of radioactive material - I told you I was going to explain this stuff. There are some things out there that haven't changed since they formed in the early days of the formation of the solar system. These are rocks that sometimes fall to the Earth and are picked up as meteorites . Meteorites can tell us a lot about the early solar system (unlike Earth rocks, which have been reprocessed many times and aren't "pristine"). When you look inside of a meteorite, you'll find, on occasion, some radioactive material. What's so important about this? First of all, radioactive material that is trapped inside of a rock must come from an energetic source, and the best candidate for that is a supernova. Also, the fact that the radioactive material was trapped inside of the rock fairly early in the history of the solar system indicates that the formation process was pretty quick. We know this because we find within meteorites short lived isotopes of aluminum 26 and iron 60 - if the supernova happened a long time ago, these isotopes would have decayed before being trapped in the meteorites. Most importantly of all, radioactive material can be used to determine the age of the solar system.

How is this done? We use the radioactive material's half-life to get the age of the material. The half-life is the time it takes for 1/2 of the radioactive material to decay, often into a non-radioactive form. For example, Iodine 129 decays into Xenon 129 with a half life of 17 million years. If there is a significant amount of Xenon 129 in a meteorite, then there must have been a lot of Iodine 129 trapped in the sample to begin with and there should still be some left. One thing about half-lifes is that you are always cutting the radioactive material in 1/2, so you never actually get down to there being no radioactive stuff remaining. If the rock were originally all Iodine 129 and only 1/8 of it is still Iodine 129, you know that it went through three half-lives (it was cut in half three times, which gives you only 1/8 of the radioactive material left). The rock would be about 3x17 = 51 million years old.

Not only is the radioactive material useful in determining the age of the rock, it also provides some valuable information by its very presence -

  1. The formation of rocks took place rather quickly since a large amount of radioactive stuff was locked into these early rocks. If there was a significant time lag, then more of the stuff would have decayed and less radioactive material would be included in the rocks. This tells us that the solar system formation process was rather quick, maybe taking only a few million years.
  2. There must have been a high energy source for the radioactive elements to be produced in the first place, before the solar nebula started the planetary formation process. The most likely source would be a type II supernova (based upon the composition of meteorites).

It is also possible that a supernova explosion occurred near the current location of the solar system. It is also possible that the explosion could have triggered the formation of our solar system! Remember, you need something to start a gas cloud collapsing - some sort of shock wave - and a supernova is a good source of not only the radioactive material but also the push needed to start the solar system forming. It is possible that the creation of our solar system was due to the death of another star! A recent study of the material expelled by supernova shows that there is more than enough material produced to create many, many planets like the Earth.

Other Solar Systems

Now that we've looked at how our solar system formed, we need to ask whether we got it right. Are we correct in our theories? The only problem with that is that we don't have much information about other solar systems (actually, we should call them planetary systems, since solar refers to our Sun). Are there any other planetary systems? Yes, there are. Actually, astronomers have found many planets outside of our solar system.

How do you do that? Actually, it isn't very easy. It is very difficult to actually see a planet next to another star, mainly because the light from the star would be so bright that it would be nearly impossible to see any little object next to it. The main method of finding planets is to see if the stars they orbit have small velocities visible in their spectra. This is sort of like the way that spectroscopic binary stars are detected - by looking at their changing spectra. The only difference here is that the star will not move very fast if it is being pulled by a puny (when compared to the star) planet. Astronomers look for velocities that are only a few m/s. In a spectrum, this corresponds to a blueshift or redshift of a fraction of an angstrom - and such a small shift is very difficult, though not impossible, to see.

Figure 7. Click to see full size image. A chart showing the orbital sizes and masses of some of the planets discovered outside of our solar system. The yellow dots represent the stars they orbit, and the blue dots represent the planets, though they are of course not to scale. The extra-solar planets' masses are given in terms of Jupiter's mass. The distances of the planets from the stars they orbit are given in A. U.s. Image from the Exoplanets Website.

Astronomers are so clever that they've come up with equipment and ways to accurately measure such small redshifts and blueshifts. There have been over 750 planets discovered so far (as of August 2013 - odds are it will be up to 800 by the time you read this). However, we should be careful in calling them planets. It is possible that some of the objects could actually be very small stars (brown dwarfs), but they usually have masses that are very similar to planets in our solar system. Most often the planet's masses are similar to Jupiter or Saturn (hundreds of times the Earth's mass) and are found within 5 AU of the star they orbit. If you click here you'll see a graph of many exoplanet masses plotted versus their orbital distances. It also shows the masses and distances of planets in our solar system for comparison. Only a few planets have been found with masses similar to the Earth or smaller. The smallest one discovered so far has a mass that is about 100 times less that of the Earth's. The masses of these objects aren't known precisely, since the tilt of their orbits makes it difficult to measure the actual size of their orbits. At this time, this method will only tell us about the most massive planets, since they will have greatest influence on the stars they orbit.

There was a breakthrough in the planet hunting area when the first picture of a extra-solar (outside of our solar system) planet was obtained. A planet was found around the star 2MASSWJ1207334-393254 (or 2M1207 for short). In this case the planet is large enough to be visible to earth-based telescopes. Images of the planet were obtained using the VLT as well as the Hubble Space Telescope. In a couple of other cases planets have been "seen" when they have passed in front of or behind the star they orbit, causing a very small eclipse of the star's light. In 2008 the Hubble Space Telescope spied a planet around the relatively bright star Fomalhaut, which also has a dusty disk around it. And at the exact time that discovery was announced, the folks at the Gemini observatory proved an image of 3 planets around another star!

While most exoplanets have been found by looking at the changing spectra of a star, it is possible to find some planets by looking for them to eclipse the star they orbit. In 2009 a spacecraft was launched which had the job of looking for such objects. The Kepler mission has already shown that it can find small objects around stars by carefully measuring the light variation caused by a planet's passage in front of the star it orbits. In August 2009, one of the first tests of the spacecraft showed that it could observe passages of even small earth-like planets in front of stars. The press release about that event is here. In March of 2011, the Kepler project announced the discovery of 1,235 candidate planets around various stars. The graphic available here shows the stars to scale, with the black dots representing the relative sizes of the planets that were possibly discovered. The lone star near the upper right is the Sun with the black dot representing Jupiter. One of the most surprising aspects of the Kepler mission is that it is only looking at a small part of the sky - about the area of your hand held at arm's length. In 2012 the gyroscopes that help stabilize and point the telescope failed, and it looked like the mission was over. But NASA is pretty clever, and they've found a way to extend the Kepler mission. They will be pointing the telescope at various places in the sky, using the light from the sun to help point it - yes, that is something that can be done. So the mission may not yet be over, and more planetary discoveries from Kepler will likely be announced.

The results from these planet searches are a bit confusing, though. Many of these large planets are found in orbits that are much closer than the Jovian planets in our solar system. How is that possible? Shouldn't only small planets be found near a star? In most cases all we know about the objects are the masses - not what they are made out of. In one case astronomers were able to estimate the density of the planet and found a value that is between that of water and rock. It is thought that this object (Gliese 436) may be made of rock, gases, and liquids in a manner that would survive around the star that it orbits. Also, many of the planets have very elliptical orbits. Why aren't their orbits circular like the planets in our solar system? There must be some way that these large planets can form close to a star. We're still working on that one. Regardless of these little dilemmas, it is still sort of neat knowing that there are quite a few planetary systems out there, so that it is possible that we are not alone!

Probably one of the most intriguing result to come from the planet searchers was the discovery of a planet around Gliese 581. This planet is located at a distance around its star that is within the star's habitable zone. This zone marks the region where water on the surface of a planet can exist as a liquid. In our solar system the zone goes from around the area of Venus out to around Mars, with the Earth right in the middle. Scientists generally view the existance of water in a liquid form as a requirement for life to exist. Personally I would have thought that coffee was more important, but that's just me. Remember, just because the planet around Gliese 581 is located within the habitable zone though doesn't mean there is life on it - it just means that water could exist as a liquid. Be careful when you read such announcements in the news about major discoveries - just because they say water could exist, doesn't mean it actually does exist on the surface of this planet. The Kepler mission has fournd nearly earth-sized planets that are located in Habitable Zones of stars similar to our Sun, but of course just because a planet is found in the correct location doesn't mean it has water on the surface. Just be on the look out for more news in the future about such systems.

While liquid water has yet to be confirmed on a planet outside of our solar system, it does appear that water in other forms exists on planets or around other stars. The first indication of this was in the spectra of a planet around the star HD209458b, which appears to show water in the planet's atmosphere. Several other worlds have been observed with water vapor in their atmospheres. While this may seem exciting, it isn't really unexpected, since water is a fairly common molecule in the Universe and we would expect to see in many locations in its various forms. Observations of a white dwarf GD 61 show evidence of asteroids containing water around it. While asteroids aren't planets, this does seem to indicate that water-based objects are present around this star, and perhaps before the star became a white dwarf there may have been planet like objects around it. Who knows? Obviously you wouldn't want to be on a planet around a white dwarf since they give off so little light, unless you like to be frozen.

No matter how you look at it, this is certainly an exciting time for planetary exploration! 2014 was a major year for discoveries, as this graph shows, but expect many more discoveries in the future.


What Are the Factors that Make the Planet Habitable?

  • It has to be a comfortable distance away from a star (Habitable Zone)
  • The stars around it have to be &lsquostable&rsquo.
  • It should not have a very low mass.
  • It must rotate on its axis and revolve.
  • It should have a molten core.
  • It should hold an atmosphere.

In the recent years, there has been a great deal of talk about finding liquid water on Mars and the possibility of life existing on the Red Planet. All this coverage has resulted in a lot of questions being raised for people always staring out into space, including a few interesting ones. For example, is the existence of water the only condition that needs to be present on a planet in order to host life? To better answer that question, let&rsquos look at the various factors that make a planet habitable.

Taking Cues from Earth

As of now, we do not have any concrete proof of the existence of life anywhere else in the universe. Therefore, in order to establish the criteria of habitability of a planet (or a natural satellite), the conditions that support life on Earth also need to be extrapolated for other celestial objects. In other words, since we haven&rsquot found proof of life anywhere else, the basic conditions that support life on Earth can be taken as a benchmark for the sustenance of life on any planet.

There are a number of conditions that a celestial body must fulfill in order to support life. These conditions involve certain geochemical, astrophysical, astrological and geophysical criteria. According to NASA, for a celestial body to sustain life, there should be &ldquoextended regions of liquid water, conditions favorable for the assembly of complex organic molecules, and energy sources to sustain metabolism.&rdquo

In gauging the habitability of a planet, a number of factors must be considered, including the planet&rsquos bulk composition, orbital properties, atmosphere, and potential chemical interactions. Some of the requisite conditions are as follow.

Location in Habitable Zone (HZ)

For a planet to sustain life, it has to be a comfortable distance away from a star, such as the sun of our solar system. Around a star, there is a shell-shaped region of space, called the Habitable Zone (HZ), where a planet can maintain liquid water on the surface. If a planet lies in this region, then there are good chances for the habitability of life on the surface. However, if life could exist without water in a certain part of the universe, then the definition of an HZ will change drastically. Also, since a star becomes more luminous as it ages, a planet must be farther away from it in the HZ to sustain life.

Stability of Stars

An artist&rsquos impression of a solar flare (Credits: Photoraidz/Shutterstock)

For a planet, it&rsquos important that the stars closest to it are stable in terms of their luminosity. Although every star&rsquos luminosity increases with time, it should not be too severe, or else it could simply burn up everything on the closest planet.

Since Earth is a terrestrial planet and is habitable, it is assumed that a planet must be made up of rocks, and not gases. Therefore, we don&rsquot expect to find life on gas giants like Jupiter, Saturn, and Uranus. However, there could be life on the cloud tops of these planets, but it is highly unlikely, as there is no surface and the gravity of these planets is very high.

Mass of the Planetary Body

A planet with low mass is not suitable for habitation because low mass means low gravity. Low gravity further means that the planet won&rsquot be able to retain an atmosphere, as constituent gases will easily reach escape velocity and be lost in open space. However, there are some exceptions to this condition: one of Jupiter&rsquos moons, Io, is a small celestial body, yet it is volcanically dynamic and has distant chances of harboring life.

Rotation and Revolution

A planet must also rotate on its axis and revolve around its parent star (like the Earth going around the sun) to be habitable. Furthermore, if life on the planet is to be given a chance to evolve, certain other conditions have to be met in its rotational motion. For example, there should be some axial tilt perpendicular to its orbit, which will result in seasons on the planet or celestial object.

A Molten Core

To sustain any type of life, a planet requires a rapidly rotating magnetic field to protect it from flares from nearby stars. This is what we call the core of the planet. A planetary core is a terrific source of geothermal energy, allows the cycling of raw materials, and spawns a magnetic field around the planet to protect it from harmful radiation. It should be noted that Mars was known to have a liquid core at one time, but its heat dissipated quickly because Mars is a smaller planet.

Holding an Atmosphere

Earth&rsquos atmosphere not only fulfills our most basic needs of providing oxygen but also keeps the planet warm by trapping carbon dioxide and other gases. It also protects life on the planet by blocking the vast majority of harmful radiation. Therefore, any habitable planet must have all the necessary conditions in place to have an atmosphere or at least a protective layer of essential gases.

As stated earlier, since we do not know of the existence of any life outside of Earth, these assumptions are deduced from the particular conditions that support life on Earth. If, however, there are organisms who can survive in altogether different conditions than what we have experienced here on Earth, then who really knows&hellipmaybe we already have company!


3.4. Why is water so important for life as we know it?

Have you noticed that everything alive needs water? Your pets, trees, and your family, too. So why do you think that is? It’s true that our bodies and other living things are made from all sorts of different things but water makes up a lot of it. Also, when you look at a globe of Earth, there really is a lot of water! Scientists have found that all living things need water. So, if we would like to try to find living things from some other planet, then maybe we should look for places that also have water.

Disciplinary Core Ideas

LS1.C: Organization for Matter and Energy Flow in Organisms: All animals need food in order to live and grow. They obtain their food from plants or from other animals. Plants need water and light to live and grow. (K-LS1-1)

ESS3.A: Natural Resources: Living things need water, air, and resources from the land, and they live in places that have the things they need. Humans use natural resources for everything they do. (K-ESS3-1)

LS2.A: Interdependent Relationships in Ecosystems: Plants depend on water and light to grow. (2-LS2-1)

ESS2.B: Plate Tectonics and Large-Scale System Interactions: Maps show where things are located. One can map the shapes and kinds of land and water in any area. (2-ESS2-2)

ESS2.C: The Roles of Water in Earth’s Surface Processes: Water is found in the ocean, rivers, lakes, and ponds. Water exists as solid ice and in liquid form. (2-ESS2-3)

Crosscutting Concepts

Patterns: Patterns in the natural world can be observed. (2-ESS2-2),(2-ESS2-3)

Big Ideas: Water is critical for life. Living things are made up of water. When looking for life beyond Earth, places that have water are of great interest.

Boundaries: Students in this grade band describe patterns of what plants and animals (including humans) need to survive. Examples of patterns could include that animals need to take in food but plants do not the different kinds of food needed by different types of animals the requirement of plants to have light and that all living things need water. (K-LS1-1)

K-8 Water in the Biosphere. In this one-hour lesson, students make their own qualitative observations outdoors. Then they examine the life they saw and how water in the biosphere is part of the greater water cycle on Earth. This lesson can stand alone or be a part of a larger unit which includes the water cycle, Earth’s water and interacting spheres. NASA . https://pmm.nasa.gov/education/lesson-plans/water-biosphere

K-8 The Water Cycle. In this one-hour lesson, students participate in a web quest to learn about the water cycle, and then build a mini-model of the water cycle to observe how water moves through Earth’s four systems. This lesson can stand alone or be a part of a larger unit which includes the water in the biosphere, Earth’s water, and interacting spheres. NASA . https://pmm.nasa.gov/education/lesson-plans/water-cycle

Grades 3-5 or Adult Emerging Learner

All living things on Earth need water. Everything from people, plants, animals, and even mushrooms and things too small to see need water to survive. Even things like cacti in a desert need some water to live. Water seems to be very important for life. Have you ever looked at a globe – there is a lot of water! Since all living things that we know of need water and many of us want to know if there could be other living things out there beyond Earth, then one thing we can do is investigate places with water beyond Earth. Mars had rivers and lakes of water a long time ago and there could still be some water deep underground there today. Also, there are some moons around other planets that have lots of water. We need to continue to investigate these places and more because if there is water, then there might be life, too.

Disciplinary Core Ideas

ESS2.A: Earth Materials and Systems: Rainfall helps to shape the land and affects the types of living things found in a region. Water, ice, wind, living organisms, and gravity break rocks, soils, and sediments into smaller particles and move them around. (4-ESS2-1) *Earth’s major systems are the geosphere (solid and molten rock, soil, and sediments), the hydrosphere (water and ice), the atmosphere (air), and the biosphere (living things, including humans). These systems interact in multiple ways to affect Earth’s surface materials and processes. The ocean supports a variety of ecosystems and organisms, shapes landforms, and influences climate. Winds and clouds in the atmosphere interact with the landforms to determine patterns of weather. (5-ESS2-1)

ESS2.B: Plate Tectonics and Large-Scale System Interactions: The locations of mountain ranges, deep ocean trenches, ocean floor structures, earthquakes, and volcanoes occur in patterns. Most earthquakes and volcanoes occur in bands that are often along the boundaries between continents and oceans. Major mountain chains form inside continents or near their edges. Maps can help locate the different land and water features areas of Earth. (4-ESS2-2)

PS3.D: Energy in Chemical Processes and Everyday Life: The energy released [from] food was once energy from the Sun that was captured by plants in the chemical process that forms plant matter (from air and water). (5-PS3-1)

LS1.C: Organization for Matter and Energy Flow in Organisms: Food provides animals with the materials they need for body repair and growth and the energy they need to maintain body warmth and for motion. (5-PS3-1) *Plants acquire their material for growth chiefly from air and water. (5-LS1-1)

LS2.A: Interdependent Relationships in Ecosystems: The food of almost any kind of animal can be traced back to plants. Organisms are related in food webs in which some animals eat plants for food and other animals eat the animals that eat plants.

LS2.B: Cycles of Matter and Energy Transfer in Ecosystems: Matter cycles between the air and soil and among plants, animals, and microbes as these organisms live and die. Organisms obtain gases, and water, from the environment, and release waste matter (gas, liquid, or solid) back into the environment. (5-LS2-1)

ESS2.C: The Roles of Water in Earth’s Surface Processes: Nearly all of Earth’s available water is in the ocean. Most freshwater is in glaciers or underground only a tiny fraction is in streams, lakes, wetlands, and the atmosphere. (5-ESS2-2)

Crosscutting Concepts

Systems and System Models: A system can be described in terms of its components and their interactions. (5-ESS2-1, 5-ESS3-1)

Big Ideas: All living things on Earth need water. Since water is vital for life on Earth, places beyond Earth that have water are of great interest. In the past, Mars had an abundance of water and it still has water today as do some of the moons around other planets in our solar system. These may be the best places to find life outside of Earth.

Boundaries: Students in this grade band are learning to graphically represent the distribution of water on Earth, including its oceans, lakes, glaciers, ground water, and polar ice caps. (5-ESS2-2)

K-8 Water in the Biosphere. In this one-hour lesson, students make their own qualitative observations outdoors. Then they examine the life they saw and how water in the biosphere is part of the greater water cycle on Earth. This lesson can stand alone or be a part of a larger unit which includes the water cycle, Earth’s water and interacting spheres. NASA . https://pmm.nasa.gov/education/lesson-plans/water-biosphere

K-8 The Water Cycle. In this one-hour lesson, students participate in a web quest to learn about the water cycle, and then build a mini-model of the water cycle to observe how water moves through Earth’s four systems. This lesson can stand alone or be a part of a larger unit which includes the water in the biosphere, Earth’s water, and interacting spheres. NASA . https://pmm.nasa.gov/education/lesson-plans/water-cycle

5-12 Astrobiology Graphic Histories. Issue 5: Astrobiology and the Earth. These astrobiology related graphic books are ingenious and artfully created to tell the story of astrobiology in a whole new way. The complete series illustrates the backbone of astrobiology from extremophiles, to exploration within and beyond the solar system. This issue explains how astrobiologists explore analog environments on Earth in order to better understand environments that could support life on other worlds like Mars. Studying Earth is key to understanding life’s potential in the universe. NASA . https://astrobiology.nasa.gov/resources/graphic-histories/

6-12 (3-5 adaptable) Project Spectra! – Planet Designer: Kelvin Climb. The focus of these lessons (17) is on how light is used to explore the Solar System. In the lesson (60 minutes) “Planet Designer: Kelvin Climb” students create a planet using a computer game and change features of the planet to increase or decrease the planet’s temperature. Students explore some of the same principles scientists use to determine how likely it is for a planet to maintain flowing water, a critical ingredient for life as we know it. Using computer simulation is a powerful tool in the search for life and the conditions for life in the solar system and beyond. University of Colorado, Boulder/NASA. http://lasp.colorado.edu/home/wp-content/uploads/2013/06/KelvinClimb_teacher_20130617.pdf

6-12 (3-5 adaptable) Project Spectra! Planet Designer: Retro Planet Red. The focus of these lessons (17) is on how light is used to explore the Solar System. In the lesson (60 minutes) “Planet Designer: Retro Planet Red” students learn about Mars’ past and present before exploring the pressure and greenhouse strength needed for Mars to have a watery surface as it had in the past. Water is a key ingredient for life. University of Colorado, Boulder/NASA. http://lasp.colorado.edu/home/wp-content/uploads/2013/06/Retro_Planet_Red_teacher_20130617.pdf

Grades 6-8 or Adult Building Learner

One attribute that is common to all living things that we know of is the need for water to survive. Even organisms that live in very dry places need water to live. Why? Why is water so important to living things? One reason that water is so important is because it’s a liquid. This means that it can move around the materials that are needed for chemical reactions. These reactions include the ability for cells to get energy in and to move waste out.

Water is made up of two atoms of hydrogen and one atom of oxygen that make a molecule. But water is a certain type of molecule called a “polar molecule”. Polar molecules have one side of the molecule that’s a bit more positively charged and the other side a little more negatively charged. This allows water to more easily break apart or dissolve other molecules. That’s why you can dissolve salt in water! There are actually a lot of other liquids that can do this but water has other advantages as well. Water is very plentiful. About 70% of the surface of Earth is covered by water, from our oceans and our lakes to our rivers and streams. It turns out that water is also plentiful in the solar system. Comets have a lot of water within them, there is ample evidence that liquid water existed on ancient Mars in great quantities, and many moons have water under their surfaces.

Water is super important for life as we know it! There might be other forms of life out there that don’t rely on water the way we do, but looking for alien life in places with lots of water is one good way to start searching for possible extraterrestrial life.

Disciplinary Core Ideas

LS1.C: Organization for Matter and Energy Flow in Organisms: Plants, algae (including phytoplankton), and many microorganisms use the energy from light to make sugars (food) from carbon dioxide from the atmosphere and water through the process of photosynthesis, which also releases oxygen. These sugars can be used immediately or stored for growth or later use. (MS-LS1-6)

PS3.A: Definitions of Energy: The term “heat” as used in everyday language refers both to thermal energy (the motion of atoms or molecules within a substance) and the transfer of that thermal energy from one object to another. In science, heat is used only for this second meaning it refers to the energy transferred due to the temperature difference between two objects. Temperature is a measure of the average kinetic energy of particles of matter. The relationship between the temperature and the total energy of a system depends on the types, states, and amounts of matter present. (MS-PS3-3, MS-PS3-4)

PS3.D: Energy in Chemical Processes and Everyday Life: The chemical reaction by which plants produce complex food molecules (sugars) requires an energy input (i.e., from sunlight) to occur. In this reaction, carbon dioxide and water combine to form carbon-based organic molecules and release oxygen.

ESS2.C: The Roles of Water in Earth’s Surface Processes: Water’s movements — both on the land and underground — cause weathering and erosion, which change the land’s surface features and create underground formations. (MS-ESS2-2)

ESS3.A: Natural Resources: Humans depend on Earth’s land, ocean, atmosphere, and biosphere for many different resources. Minerals, fresh water, and biosphere resources are limited, and many are not renewable or replaceable over human lifetimes. (MS-ESS3-1)

Crosscutting Concepts

Structure and Function: Complex and microscopic structures and systems can be visualized, modeled, and used to describe how their function depends on the relationships among its parts, therefore complex natural structures/systems can be analyzed to determine how they function. (MS-LS1-2)

Big Ideas: All living things on Earth need water. It is critical to cellular function. Since water is vital for life on Earth, places beyond Earth that have water are of great interest. As a polar molecule, it has specific chemical properties, like the ability to dissolve other molecules. Water has been found in other places beyond Earth, like Mars and meteorites. Because water is so universal, astrobiologists look for water on other worlds as an indicator of possible life.

Boundaries: Students in this grade band construct a scientific explanation based on evidence for how the uneven distributions of Earth’s mineral, energy, and groundwater resources are the result of past and current geoscience processes. Emphasis is on how these resources are limited and typically non-renewable. (MS-ESS3-1)

K-8 Water in the Biosphere. In this one-hour lesson, students make their own qualitative observations outdoors. Then they examine the life they saw and how water in the biosphere is part of the greater water cycle on Earth. This lesson can stand alone or be a part of a larger unit which includes the water cycle, Earth’s water and interacting spheres. NASA . https://pmm.nasa.gov/education/lesson-plans/water-biosphere

K-8 The Water Cycle. In this one-hour lesson, students participate in a web quest to learn about the water cycle, and then build a mini-model of the water cycle to observe how water moves through Earth’s four systems. This lesson can stand alone or be a part of a larger unit which includes the water in the biosphere, Earth’s water, and interacting spheres. NASA . https://pmm.nasa.gov/education/lesson-plans/water-cycle

5-12 Astrobiology Graphic Histories. Issue 5: Astrobiology and the Earth. These astrobiology related graphic books are ingenious and artfully created to tell the story of astrobiology in a whole new way. The complete series illustrates the backbone of astrobiology from extremophiles, to exploration within and beyond the solar system. This issue explains how astrobiologists explore analog environments on Earth in order to better understand environments that could support life on other worlds like Mars. Studying Earth is key to understanding life’s potential in the universe. NASA . https://astrobiology.nasa.gov/resources/graphic-histories/

6-12 Big Picture Science: Rife with Life. “Follow the water” is the mantra of those who search for life beyond Earth. Where there’s water, there may be life. This podcast features a tour of watery solar system bodies that hold promise for biology: Europa, Enceladus, Mars & Titan. SETI scientist Seth Shostak hosts this radio show on various topics in science, cosmology, physics, astronomy and astrobiology. Shostak interviews experts and explains important discoveries and concepts including in his weekly 50-minute shows. http://www.bigpicturescience.org/episodes/Rife_with_Life and http://www.bigpicturescience.org/Astrobiology_Index

6-12 Astrobiology Math. This collection of math problems provides an authentic glimpse of modern astrobiology science and engineering issues, often involving actual research data. Students explore concepts in astrobiology through calculations. Relevant topics include Ice or Water? (page 49) and Ice to Water…The Power of a Little Warmth! (page 51). NASA . https://www.nasa.gov/pdf/637832main_Astrobiology_Math.pdf

6-12 (3-5 adaptable) Project Spectra! – Planet Designer: Kelvin Climb. The focus of these lessons (17) is on how light is used to explore the Solar System. In the lesson (60 minutes) “Planet Designer: Kelvin Climb” students create a planet using a computer game and change features of the planet to increase or decrease the planet’s temperature. Students explore some of the same principles scientists use to determine how likely it is for a planet to maintain flowing water, a critical ingredient for life as we know it. Using computer simulation is a powerful tool in the search for life and the conditions for life in the solar system and beyond. University of Colorado, Boulder/NASA. http://lasp.colorado.edu/home/wp-content/uploads/2013/06/KelvinClimb_teacher_20130617.pdf

6-12 (3-5 adaptable) Project Spectra! Planet Designer: Retro Planet Red. The focus of these lessons (17) is on how light is used to explore the Solar System. In the lesson (60 minutes) “Planet Designer: Retro Planet Red” students learn about Mars’ past and present before exploring the pressure and greenhouse strength needed for Mars to have a watery surface as it had in the past. Water is a key ingredient for life. University of Colorado, Boulder/NASA. http://lasp.colorado.edu/home/wp-content/uploads/2013/06/Retro_Planet_Red_teacher_20130617.pdf

8-10 SpaceMath Problem 275: Water on the Moon! Students estimate the amount of water on the moon using data from Deep Impact/EPOXI and NASA ’s Moon Mineralogy Mapper experiment on the Chandrayaan-1 spacecraft. [Topics: geometry, spherical volumes and surface areas, scientific notation] https://spacemath.gsfc.nasa.gov/moon/6Page11.pdf

8-10 SpaceMath Problem 264: Water on Planetary Surfaces. Students work with watts and Joules to study melting ice. [Topics: unit conversion, rates] https://spacemath.gsfc.nasa.gov/astrob/Astro3.pdf

8-10 SpaceMath Problem 121: Ice on Mercury? Since the 1990’s, radio astronomers have mapped Mercury. An outstanding curiosity is that in the polar regions, some craters appear to have ‘anomalous reflectivity’ in the shadowed areas of these craters. One interpretation is that this is caused by subsurface ice. The MESSENGER spacecraft hopes to explore this issue in the next few years. In this activity, students measure the surface areas of these potential ice deposits and calculate the volume of water that they imply. [Topics: area of a circle volume, density, unit conversion] https://spacemath.gsfc.nasa.gov/planets/4Page23.pdf

Grades 9-12 or Adult Sophisticated Learner

All life on this planet needs water to survive. Some life can live with very little water in extremely dry places but they still need water. As we strive to find life beyond Earth, it is important to consider what life on Earth tells us about where to look. Why is water so important for life? Water supports cell functions. All organisms are made of cells, from microbes to the largest animals. All of life’s functions are completed within cells. Life needs chemical reactions to take place in order to gain energy, grow, and get rid of waste. Water is a liquid which allows the chemistry of life to take place. It is also a polar molecule which allows most other molecules to be dissolved. Because of this, we call water a “solvent”. Having such a good solvent as water is critical for the functions of life. But there are also some other reasons why water is so important:

Water is plentiful! Hydrogen is the most plentiful element in the universe and oxygen the most plentiful in Earth’s crust. On Earth, about 70% of the surface is covered by water. But there’s also lots of water in other places in our solar system. For instance, we’ve found many lines of evidence that lots of water existed on the surface of Mars during its early times, and Mars currently has a lot of frozen water under its surface. Comets contain mostly water ice. There are lots of moons in our solar system that are made of a lot of water ice, and there are even some moons with liquid water oceans under their icy crusts (like Europa and Enceladus).

Water still has other advantages as a solvent for life. For instance, water stays in the liquid phase over a large range of temperatures compared to some other solvents. That allows more places to have the potential for liquid water. It also has a high heat capacity. This means that water offers some protection to organisms from quick or drastic temperature changes.

Water also has an interesting property with regard to the density of ice. For many molecules, the solid has a higher density than the liquid. So, for most molecules, the solid would sink in the liquid. But this isn’t the case with water. For water, ice is actually less dense than liquid water. This is why ice floats! If this didn’t happen, then all of the organisms that live in the bottoms of lakes in the winter time would be completely frozen. But, even worse, during times in our planet’s history when the world has become very cold (causing what we call Snowball Earth), if frozen water sank, then all of Earth’s ocean life would have become frozen and maybe died!

If we want to understand how life works, then it’s really important to understand the chemistry of water. And astrobiologists who are wondering if we’re alone in the universe need to be aware of the potential for water to be important for other kinds of life as well. Right now, we’re investigating worlds like Enceladus and Europa, Mars, and other solar system bodies that show signs of water. Also, beyond our solar system, we’re looking for exoplanets that have the potential for liquid water at their surfaces, since they might be important places for us to look for possible extraterrestrial life.

Disciplinary Core Ideas

PS3.A: Definitions of Energy: Motion energy is properly called kinetic energy it is proportional to the mass of the moving object and grows with the square of its speed. (MS-PS3-1) ▪A system of objects may also contain stored (potential) energy, depending on their relative positions. (MS-PS3-2) Temperature is a measure of the average kinetic energy of particles of matter. The relationship between the temperature and the total energy of a system depends on the types, states, and amounts of matter present. (MS-PS3-3, MS-PS3-4)

PS3.D: Energy in Chemical Processes and Everyday Life: The chemical reaction by which plants produce complex food molecules (sugars) requires an energy input (i.e., from sunlight) to occur. In this reaction, carbon dioxide and water combine to form carbon-based organic molecules and release oxygen. (MS-LS1-6)

LS2.C: Ecosystem Dynamics, Functioning, and Resilience: Biodiversity describes the variety of species found in Earth’s terrestrial and oceanic ecosystems. The completeness or integrity of an ecosystem’s biodiversity is often used as a measure of its health. (MS-LS2-5)

ESS2.A: Earth’s Materials and Systems: All Earth processes are the result of energy flowing and matter cycling within and among the planet’s systems. This energy is derived from the Sun and Earth’s hot interior. The energy that flows and matter that cycles produce chemical and physical changes in Earth’s materials and living organisms. (MS-ESS2-1)

ESS2.C: The Roles of Water in Earth’s Surface Processes: Water continually cycles among land, ocean, and atmosphere via transpiration, evaporation, condensation and crystallization, and precipitation, as well as downhill flows on land. (MS-ESS2-4) ▪ Global movements of water and its changes in form are propelled by sunlight and gravity. (MS-ESS2-4)

ESS3.A: Natural Resources: Humans depend on Earth’s land, ocean, atmosphere, and biosphere for many different resources. Minerals, fresh water, and biosphere resources are limited, and many are not renewable or replaceable over human lifetimes. These resources are distributed unevenly around the planet as a result of past geologic processes. (MS-ESS3-1)

ESS2.D: Weather and Climate: Weather and climate are influenced by interactions involving sunlight, the ocean, the atmosphere, ice, landforms, and living things. These interactions vary with latitude, altitude, and local and regional geography, all of which can affect oceanic and atmospheric flow patterns. (MS-ESS2-6) The ocean exerts a major influence on weather and climate by absorbing energy from the Sun, releasing it over time, and globally redistributing it through ocean currents. (MS-ESS2-6)

Crosscutting Concepts

Stability and Change: Much of science deals with constructing explanations of how things change and how they remain stable. (HS-ESS2-7)

Big Ideas: All living things need water. Water is critical to cellular function, chemical reactions, and thermal regulation. Water is less dense when a solid and stays in the same state over a wide temperature range. It is abundant on Earth and a common thread between all living things. Water has been found in other places beyond Earth, like Mars and meteorites. Because water is so universal, Astrobiologist look for water on the surface and atmosphere of exoplanets as an indicator that the planet could support life. Understanding the chemistry of water is important to understanding how life works.

Boundaries: In this grade band, students investigate the properties of water and its effects on Earth materials and surface processes including chemical investigations like chemical weathering and recrystallization. (HS-ESS2-5)

5-12 Astrobiology Graphic Histories. Issue 5: Astrobiology and the Earth. These astrobiology related graphic books are ingenious and artfully created to tell the story of astrobiology in a whole new way. The complete series illustrates the backbone of astrobiology from extremophiles, to exploration within and beyond the solar system. This issue explains how astrobiologists explore analog environments on Earth in order to better understand environments that could support life on other worlds like Mars. Studying Earth is key to understanding life’s potential in the universe. NASA . https://astrobiology.nasa.gov/resources/graphic-histories/

6-12 Big Picture Science: Rife with Life. “Follow the water” is the mantra of those who search for life beyond Earth. Where there’s water, there may be life. This podcast features a tour of watery solar system bodies that hold promise for biology: Europa, Enceladus, Mars & Titan. SETI scientist Seth Shostak hosts this radio show on various topics in science, cosmology, physics, astronomy and astrobiology. Shostak interviews experts and explains important discoveries and concepts including in his weekly 50-minute shows. http://www.bigpicturescience.org/episodes/Rife_with_Life and http://www.bigpicturescience.org/Astrobiology_Index

6-12 Astrobiology Math. This collection of math problems provides an authentic glimpse of modern astrobiology science and engineering issues, often involving actual research data. Students explore concepts in astrobiology through calculations. Relevant topics include Ice or Water? (page 49) and Ice to Water…The Power of a Little Warmth! (page 51). NASA . https://www.nasa.gov/pdf/637832main_Astrobiology_Math.pdf

6-12 (3-5 adaptable) Project Spectra! – Planet Designer: Kelvin Climb. The focus of these lessons (17) is on how light is used to explore the Solar System. In the lesson (60 minutes) “Planet Designer: Kelvin Climb” students create a planet using a computer game and change features of the planet to increase or decrease the planet’s temperature. Students explore some of the same principles scientists use to determine how likely it is for a planet to maintain flowing water, a critical ingredient for life as we know it. Using computer simulation is a powerful tool in the search for life and the conditions for life in the solar system and beyond. University of Colorado, Boulder/NASA. http://lasp.colorado.edu/home/wp-content/uploads/2013/06/KelvinClimb_teacher_20130617.pdf

6-12 (3-5 adaptable) Project Spectra! Planet Designer: Retro Planet Red. The focus of these lessons (17) is on how light is used to explore the Solar System. In the lesson (60 minutes) “Planet Designer: Retro Planet Red” students learn about Mars’ past and present before exploring the pressure and greenhouse strength needed for Mars to have a watery surface as it had in the past. Water is a key ingredient for life. University of Colorado, Boulder/NASA. http://lasp.colorado.edu/home/wp-content/uploads/2013/06/Retro_Planet_Red_teacher_20130617.pdf

8-10 SpaceMath Problem 275: Water on the Moon! Students estimate the amount of water on the moon using data from Deep Impact/EPOXI and NASA ’s Moon Mineralogy Mapper experiment on the Chandrayaan-1 spacecraft. [Topics: geometry, spherical volumes and surface areas, scientific notation] https://spacemath.gsfc.nasa.gov/moon/6Page11.pdf

8-10 SpaceMath Problem 264: Water on Planetary Surfaces. Students work with watts and Joules to study melting ice. [Topics: unit conversion, rates] https://spacemath.gsfc.nasa.gov/astrob/Astro3.pdf

8-10 SpaceMath Problem 121: Ice on Mercury? Since the 1990’s, radio astronomers have mapped Mercury. An outstanding curiosity is that in the polar regions, some craters appear to have ‘anomalous reflectivity’ in the shadowed areas of these craters. One interpretation is that this is caused by subsurface ice. The MESSENGER spacecraft hopes to explore this issue in the next few years. In this activity, students measure the surface areas of these potential ice deposits and calculate the volume of water that they imply. [Topics: area of a circle volume, density, unit conversion] https://spacemath.gsfc.nasa.gov/planets/4Page23.pdf

9-12 SpaceMath Problem 338: Asteroids and Ice. Students calculate how much ice may be present on the asteroid 24-Themis based on recent discoveries by NASA [Topics: mass=density x volume volume of a spherical shell] https://spacemath.gsfc.nasa.gov/astrob/6Page154.pdf

9-12 SpaceMath Problem 287: LCROSS Sees Water on the Moon. Students use information about the plume created by the LCROSS impactor to estimate the (lower-limit) concentration of water in the lunar regolith in a shadowed crater. [Topics: geometry volumes mass=density x volume] https://spacemath.gsfc.nasa.gov/moon/6Page66.pdf

Storyline Extensions

Water is so cool!

The range of temperatures at which water stays liquid is rather large compared to most other common solvents. For instance, at sea level methane freezes at -182 Celsius © and boils at -162 C (a range of 21 C) and ammonia freezes at -78 C and boils at -34 C (a range of 44 C), meanwhile water freezes at 0 C and boils at 100 C (a range of 100 C). This means that the range of temperatures where water is liquid is more than twice that of ammonia and almost five times more than that of methane.

Water has a high surface tension. This means that that the molecules at the surface of a body of water are attracted to each other and hold each other together. You can see this yourself by filling a glass with water to the very tippy top and then seeing how many more drops of water you can get into it. You’ll be surprised to find that you can actually get a good bit more water into the glass! The high surface tension of water is also why some insects, like water striders, are able to move around on top of water without sinking into it. It also is related to something called “capillary action”, which is used by many plants to draw water up from the ground against gravity.

It’s actually really rare for a solvent to be more dense as a liquid than as a solid. We know of other elements and molecules that are more dense as liquids, but it’s far more common for the solid form of a substance to be more dense.

[note: this is fairly advanced] Oxygen is a member of the group of elements known as the “oxygen family” (also sometimes called the chalcogens). These are the elements in the periodic table that are in group 16 (the vertical column starting with oxygen and going down). They include oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po). All of these elements can form bonds with two hydrogen atoms. However, none of the other chalcogens come close to oxygen in its large range of temperatures where it is a liquid. This is because oxygen is much more electronegative (much greedier for electrons) and makes a far more polar molecule than the others. This greater polarity leads to stronger hydrogen bonding and the greater range of temperatures for liquid water.

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Our Milky Way Galaxy: How Big is Space?

When we talk about the enormity of the cosmos, it&rsquos easy to toss out big numbers &ndash but far more difficult to wrap our minds around just how large, how far, and how numerous celestial bodies really are.

To get a better sense, for instance, of the true distances to exoplanets &ndash planets around other stars &ndash we might start with the theater in which we find them, the Milky Way galaxy.

What is a galaxy, anyway?

Our galaxy is a gravitationally bound collection of stars, swirling in a spiral through space. Based on the deepest images obtained so far, it&rsquos one of about 2 trillion galaxies in the observable universe. Groups of them are bound into clusters of galaxies, and these into superclusters the superclusters are arranged in immense sheets stretching across the universe, interspersed with dark voids and lending the whole a kind of spiderweb structure. Our galaxy probably contains 100 to 400 billion stars, and is about 100,000 light-years across. That sounds huge, and it is, at least until we start comparing it to other galaxies. Our neighboring Andromeda galaxy, for example, is some 220,000 light-years wide. Another galaxy, IC 1101, spans as much as 4 million light-years.

Ok, fine, but what the heck is a light-year?

Glad you asked. It&rsquos one of the most commonly used celestial yardsticks, the distance light travels in one year. Light zips along through interstellar space at 186,000 miles (300,000 kilometers) per second (more than 66 trips across the entire United States, in one second). Multiply that by all the seconds in one year, and you get 5.8 trillion miles (9.5 trillion kilometers). Just for reference, Earth is about eight light minutes from the Sun. A trip at light speed to the very edge of our solar system &ndash the farthest reaches of the Oort Cloud, a collection of dormant comets way, way out there &ndash would take about 1.87 years. Keep going to Proxima Centauri, our nearest neighboring star, and plan on arriving in 4.25 years at light speed.

If you could travel at light speed. Which, unless you&rsquore a photon (a particle of light), you can&rsquot, and, by current physics, might never be possible. But I digress.

Can we get back to those&hellipX-planets?

Exoplanets. Let&rsquos toss around some more big numbers. First, how many are there? Based on observations made by NASA&rsquos Kepler space telescope, we can confidently predict that every star you see in the sky probably hosts at least one planet. Realistically, we&rsquore most likely talking about multi-planet systems rather than just single planets. In our galaxy of hundreds of billions of stars, this pushes the number of planets potentially into the trillions. Confirmed exoplanet detections (made by Kepler and other telescopes, both in space and on the ground) now come to more than 3,900 &ndash and that&rsquos from looking at only tiny slices of our galaxy. Many of these are small, rocky worlds that might be at the right temperature for liquid water to pool on their surfaces.

Where is the nearest one of these exoplanets?

It&rsquos a small, probably rocky planet orbiting Proxima Centauri &ndash as mentioned before, the next star over. A little more than four light-years away, or 24 trillion miles as the crow flies. If an airline offered a flight there by jet, it would take 5 million years. Not much is known about this world its close orbit and the periodic flaring of its star lower its chances of being habitable.

I&rsquod also point you to the TRAPPIST-1 system: seven planets, all roughly in Earth&rsquos size range, orbiting a red dwarf star about 40 light-years away. They are very likely rocky, with four in the &ldquohabitable zone&rdquo &ndash the orbital distance allowing potential liquid water on the surface. And computer modeling shows some have a good chance of being watery &ndash or icy &ndash worlds. In the next few years, we might learn whether they have atmospheres or oceans, or even signs of habitability.

Ok. Thanks. I need to go.

I understand. You&rsquore short on time. That reminds me: Did you know time slows down in the presence of gravity?

I know it&rsquos slowing down right now.

I guess that&rsquos a discussion for another time.

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Presidential Suite

These strawberries must be collected during the boss chase with Mr. Oshiro!

Strawberry #23

When you first come across switches in the chase, you’ll be near the strawberry. When grabbing the second switch, you need to bounce off of Mr. Oshiro’s head in order to get enough height to clear the black matter and grab the floating strawberry.

Strawberry #24

This strawberry is easy to spot. During the chase, you see a small structure that you have to go through. The strawberry is at the top. Climb the left wall and jump through the gap to grab the strawberry and land on the other side.

Strawberry #25

The final strawberry for chapter 3 is at the tail end of the chase. You’ll see it hanging low over some black matter. Drop down and dash to the right to snag it and grab the wall. Climb up to secure it!


Watch the video: Top 10 Most Insane Waterslides (August 2022).