Astronomy

How do we define temperature in outer space?

How do we define temperature in outer space?


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I was recently reading an article on space.com about : What's the Temperature of Outer Space.

They said :

Some parts of space are hot! Gas between stars, as well as the solar wind, both seem to be what we call "empty space," yet they can be more than a thousand degrees, even millions of degrees.

But here is my question - "How do we define temperature in outer space?"

We perceive temperature as the average translational kinetic energy associated with the disordered motion of atoms and moleculules, so how can the temperature be so high at some places, if there isn't any (or very, very few) molecules out there in vacuum?


First of all, the medium they are mentioning is far from empty even though it is much less dense than what we do know on Earth (see this question for more details).

Then, the problem with temperature in astrophysics is that the medium you study is in general far from thermodynamic equilibrium (thermodynamic equilibrium means that there are no flows of enery or matter within the system and with the outside of the system).

Most commonly, however, we can use another flavor of equilibrium to estimate temperature. This is the kinetic equilibrium: since most collisions are elastic (meaning that the energy is conserved), particles velocities will follow a Maxwell-Boltzmann distribution. Depending on the ionization fraction (how much is your medium ionized?) this temperature will either the kinetic temperature of electrons or the kinetic temperature of hydrogen.

Then, if you want to understand these high temperatures, you have to take into account the photoionization rate and the photoelectric heating (a process in which you eject electron from the matter of the studied medium due to UV absorption). The thermal state of the medium then depends on the equilibrium between the energy absorption by the matter and the re-emission of this energy in thermal radiation. In this framework, the energy that can be absorbed comes from the interstellar radiation field (ISRF). In the solar neighborhood, it is dominated by six different types of radiation: galactic synchrotron emission of relativistic electrons (electrons accelerated to tremendous speed in the galaxy), the cosmic microwave background, the infrared emission of the matter heated by the light emitted by stars, emission from ionized plasma, the light emitted by stars itself, and lastly X-rays from hot plasma.

References:


In the absense of any particles, we evaluate temperature by the radiation wavelengths seen. In "empty space" only the cosmic background radiation exists, so we mark it pretty cold. see, for example, this note.

However, if you look at a chunk of space containing even a few particles, then the temperature is defined based on the mean kinetic energy of the particles, or more precisely, the amount of entropy present. See temperature as intensive variable


You are correct in your definition of heat, in that it does need a medium. The "heat" in space, however, is radiant. It does need a medium in order to be called heat, but the energy is there. Scientists measure the radiant energy in space to see how hot it would be if it were in a medium. The space is not physically hot, but the energy there means that if you were to travel there, the energy would he transferred into you, and you would become hot.


What is Space Plasma?

The universe is made of up of space plasma, the fourth state of matter.

The universe is made of up of space plasma. Plasma is the word given to the fourth state of matter (solid, liquid, gas, plasma). A plasma is a gas that is so hot that some or all its constituent atoms are split up into electrons and ions, which can move independently of each other. Because they are made up of electrically charged particles, plasmas can be strongly influenced by electrostatic and electromagnetic fields and forces, which can lead to very complex and interesting behaviour.

Plasmas are found throughout the Solar System and beyond: in the solar corona and solar wind, in the magnetospheres of the Earth and other planets, in tails of comets, in the inter-stellar and inter-galactic media and in the accretion disks around black holes. There are also plasmas here on Earth, ranging from the inside of a nuclear fusion reactor to a candle flame.

In the Space Plasma Physics Group, we study plasmas in the Earth's magnetosphere and the solar wind, and what happens when they interact.

Despite what a lot of people think, space isn't actually empty, and the Earth's magnetosphere is no exception! The magnetosphere is full of plasma of many different temperatures and densities - though most of it is too tenuous to see with the naked eye or even with a telescope. The air at sea level has a 100,000,000,000,000,000,000 particles per cubic centimetre and a temperature of 20 degrees C. The densest, coldest part of the magnetosphere, the plasmasphere has between 10 and 10,000 particles per cubic centimetre and a temperature of 58,000 degrees C - hotter than the surface of the Sun!

All of the plasma in the magnetosphere comes from either the ionopshere or the solar wind. One of the great mysteries of the magnetosphere is how all of these different plasmas are produced from only those two starting points.

Images from space have shown us that the aurora form ovals centred around Earth's magnetic poles. The radius of these ovals get larger and the aurora move to lower latitudes when the Earth's magnetosphere is strongly affected by the solar wind or engulfed by a coronal mass ejection, a massive explosion of solar plasma and magnetic field that travels through the solar system, often at speeds much faster than the normal solar wind.

During the strongest events the auroral oval can reach as far south as the UK. Sign up to aurorawatch to receive alerts when you can see the aurora in the UK!

It is only by properly understanding the magnetosphere and how it interacts with the solar wind that we can accurately predict and mitigate the effects of space weather on our society.


Space observatory

A space observatory is any instrument in outer space which is used for observation of distant planets, galaxies, and other outer space objects.

A large number of observatories have been launched into orbit, and most of them have greatly enhanced our knowledge of the cosmos.

Performing astronomy from the Earth's surface is limited by the filtering and distortion of electromagnetic radiation due to the Earth's atmosphere.

This makes it desirable to place astrononomical observation devices into space.

As a telescope orbits the Earth outside the atmosphere it is subject neither to twinkling (distortion due to thermal turbulences of the air) nor to light pollution from artificial light sources on the Earth.

But space-based astronomy is even more important for frequency ranges which are outside of the optic window and the radio window, the only two wavelength ranges of the electromagnetic spectrum that are not severely attenuated by the atmosphere.

For example, X-ray astronomy is nearly impossible when done from the Earth, and has reached its current important stand within astronomy only due to orbiting satellites with X-ray telescopes such as the Chandra observatory or XMM-Newton observatory.


Pressure in Outer Space

Pressure is everywhere. The earth's atmosphere exerts pressure on us right now. Although the pressure at an point of earth's surface is the equal. This is true if you are at the same altitude on the earth as someone else. Pressure always acts perpendicular to the surface.

Outer space is a very hostile place. Because of the very low pressure in outer space humans have to be trapped in a spacesuit in fear of the boiling of their bodily liquids. The fluids would not be able to evaporate entirely primarily because of the rapid loss of heat energy. There is no place like home, where the average pressure is 101,321 pascal (Pa). The formula P = F/A is used to find pressure.

In outer space one would also face extreme changes in temperature. The temperature in the sunlight is 120 °C, which is higher than the boiling point of water. In the shade the temperature is about -100 °C, way below the freezing point of water. The body tissue (skin, heart, other internal organs) would expand because of the boiling fluids. However, they would not "explode"as depicted in some science fiction movies, such as "Total Recall". Death would occur within one minute.

The pressure in outer space is so low that many consider it as non-existant. It has a pressure of 1.322 × 10 󔼓 Pa. Pressure may be detected from the molecule of air or water hitting you. Since there is very little air and hardly ever water hitting you in space, pressure is almost zero or negligible.


How do we define temperature in outer space? - Astronomy

First of all, let me refer you to the answer to another question, on temperatures in space. That posting talks a bit about some of the many different temperatures that exist in different conditions in space.

We don't actually measure a temperature of space itself. Temperature is associated with motions of atoms and molecules, and so it doesn't have any real meaning for the vacuum of space. We can, however, talk about the temperature of atoms in space, and the temperature of radiation (light) travelling through space.

Because we don't actually travel far into space, we must make temperature measurements using spectra--essentially, we pass light through a prism (or something similar), and see how much light is coming to us from different wavelengths.

Light from any hot, dense, glowing object (the Sun is a good example) follows what we call a continuous spectrum. That means that we see light at all wavelengths, the full rainbow. More light comes at some wavelengths than others, however, and the wavelength at which most of the light comes out tells us the temperature of the emitting object. The hotter the object, the bluer the light that it emits. If you were travelling in the Solar System, for example, you would be bathed in light coming from the Sun, which has a temperature of about 6000 K.

Another measure of the temperature in space is how quickly the atoms and molecules that fill space are moving around. To measure this, we also use spectra. The gas in space, however, doesn't emit a continuous spectrum, but instead emits emissions lines. That means that we see light at only certain, specific wavelengths, that depend upon what atoms are present, and how hot the gas is (you may also want to look at an earlier posting on spectra).

A simple way to think of an atom (actually oversimplified, but very useful) is to imagine electrons orbiting the nucleus, somewhat like the planets orbiting the Sun. Unlike the planets, however, the electrons can only have certain orbits. To move an electron from an orbit close to the nucleus to one further away takes energy, either from a collision with another atom, or by absorbing a photon. An electron in an orbit far from the nucleus, however, will want to "fall" to one that is closer. It emits energy as it does so, which comes out in the form of one or more photons (one photon for each "jump" the electron makes from one orbit to another).

If the difference in energy between two orbits is larger, then a more energetic (bluer) photon is emitted when the electron jumps from the higher to the lower orbit. Because the spacing of the orbits is different for different atoms, we can use the spectra to determine the chemical makeup of a gas that emits an emission-line spectrum.

We can also use the spectrum to measure the temperature of the gas. In a "typical" interstellar gas cloud, atoms are ionized (electrons are stripped from the atoms) when they absorb ultraviolet photons. The free electrons then collide with other atoms, heating the gas. Some electrons will collide with atoms that have lost one or more electrons, and will "recombine," that is they will become bound to the atom, emitting photons in the process. Other collisions will excite electrons in atoms to higher orbits, and they will emit photons as they "fall" back to lower orbits. The photons that are emitted by these processes are lost to the gas (a few end up in our telescopes), and help to cool the gas.

To measure the temperature of the gas, we could, for example, look at how many photons we are receiving from atoms of a given chemical element that have lost different numbers of electrons. More electrons being stripped means a hotter gas. We can also look at photons coming from transitions within the atoms. If we see more transitions that result from electrons that start at higher levels, then it means that the atoms are more highly "excited," that is, the gas is hotter, and so more electrons are being "kicked up" to higher energy levels by collisions.


What is space?

In space, no one can hear you scream. This is because there is no air in space – it is a vacuum. Sound waves cannot travel through a vacuum.

'Outer space' begins about 100 km above the Earth, where the shell of air around our planet disappears. With no air to scatter sunlight and produce a blue sky, space appears as a black blanket dotted with stars.

Space is usually regarded as being completely empty. But this is not true. The vast gaps between the stars and planets are filled with huge amounts of thinly spread gas and dust. Even the emptiest parts of space contain at least a few hundred atoms or molecules per cubic metre.

Space is also filled with many forms of radiation that are dangerous to astronauts. Much of this infrared and ultraviolet radiation comes from the Sun. High energy X-rays, gamma rays and cosmic rays – particles travelling close to the speed of light – arrive from distant star systems.


Here's a quick and dirty approximation:

Approximate a human with a water-sphere of radius $r$. Assume that blood circulation keeps the body temperature homogenous and that the skin keeps the water from boiling off (this isn't realistic but I figured this was the kind of situation you were thinking of). If we assume the sphere is a perfect blackbody, the heat loss due to thermal radiation is given by the Stefan-Boltzmann law:

$ P_r=sigma T^4cdot A=sigma T^4cdot 4pi r^2 $

where $T$ is the temperature of the water and $A$ is the surface area of the sphere. The rate of temperature change will be:

where $m$ is the mass of the sphere, $C$ is the specific heat capacity of water,$ ho$ is the density of water and $V$ is the volume of the sphere. Hence, we get a differntial equation of the form:

If we make the ansatz: $ T(t)=a(t+b)^n $

and put it into the above equation, we get:

If we assume $r$ is 0.5 m, we get:

If we assume that the temperature at $t=0$ is $37$ degrees C, which is approximately $310 K$, you get:

$ 310=1.6cdot 10^4b^<-frac<1><3>>Rightarrow b=left(frac<1.6cdot 10^4><310> ight)^3approx 1.38cdot 10^5 $

Here I have plotted the time evolution of the temperature according to this formula:

As you see, it takes approximately 65000 s (almost 18 hours) for the sphere to freeze. This is obviously something of a worst case scenario. I have not included the effect of heat produced by the human body, incoming (solar) radiation, less than perfect emissitivty, possible insulation, etc. These could make it take much longer or even prevent cooling, depending on the assumptions.

The answer by jkej is good. I will add onto the discussion by using numerical software. Here is syntax in Maple that solves the equation already discussed.

$ T(t) = left( 3 alpha t + T_0^3 ight)^<-frac<1><3>>$

This is consistent with the other answer. For reference, $alpha=1/(3 a^3)$. Since we have a value for $a$ we can get alpha trivially. Now let's try it with heat production! This is solving the following differential equation.

As the time limits to infinity, we expect the function to level out at $(eta/alpha)^<1/4>$. If you assume that the heat production is 100 Watts, then:

The syntax to solve the differential equation is:

Getting the answer to a coherent format takes some algebra wrestling. For simplification, I collected terms to insert the final temperature calculated before. The "solution" to the differential equation is then:

This has to be solved at every time step. Here's what I produced:

The time frame is still about the same. Nothing really interesting to speak of. It should be noted that the astronaut's mass comes out to like $520 kg$, which is fairly unrealistic. That's a major factor in the time frames being as long as they are.

In the above graph the astronaut freezes in about 11 hours. While there is some correction needed for the radiative area exposed to space, the linear dimension of the astronaut exceeds a meter in the vertical, so there are corrections in both directions. While the effective radiative area should still probably be revised downward, it won't compare to the downward revision to the mass. So in practice you will freeze sooner. Maybe you'll freeze in 4 hours or so. You'll be comatose at 31 degrees C, which linearly interpolated, only takes about 13% of the time, or 39 minutes. Hypothermia should only take 12-13 minutes. Loss of hope, probably sooner.

This made me think - if you're stranded floating in space, curl in the fetal position so you won't radiate heat as fast.

I realized the above graph is technically wrong. After it crosses the freezing point the heat production shuts down. Because you'd be dead.


Colder Than Empty Space? How The Boomerang Nebula Does It

A color-coded image of the Boomerang Nebula, as taken by the Hubble Space Telescope. Image credit: . [+] NASA.

Anywhere you go in the Universe, there are heat sources to contend with. The farther away you are from all of them, the colder it gets. At a distance of 93 million miles from the Sun, Earth is kept at a modest

300 K, a temperature that would be nearly 50º cooler if it weren't for our atmosphere. Move farther out, and the Sun becomes progressively less and less able to heat things up. Pluto, for instance, is just 44 K: cold enough that liquid nitrogen freezes. And we can go to an even more isolated place, like interstellar space, where the nearest stars are light years away.

The dark nebula Barnard 68, now known to be a molecular cloud called a Bok globule, has a . [+] temperature of less than 20 K. Image credit: ESO, via http://www.eso.org/public/images/eso0102a/.

The cold molecular clouds that roam, isolated, throughout the galaxy are even colder, just 10 K to 20 K above absolute zero. As stars, supernovae, cosmic rays, stellar winds and more all provide energy to the galaxy as a whole, it's hard to get much cooler than that within the Milky Way. But if you head to intergalactic space, millions of light years from the nearest stars, the only thing to keep you warm will be the leftover glow from the Big Bang, the Cosmic Microwave Background.

If we could see microwave light, the night sky would look like the green oval at a temperature of . [+] 2.7 K, with the "noise" in the center contributed by hotter contributions from our galactic plane. Image credit: NASA / WMAP science team, of the discovery of the CMB in 1965 by Arno Penzias and Bob Wilson.

At less than 3º C above absolute zero, these barely-detectable photons are the only heat source around. Since every location in the Universe is constantly bombarded by these infrared, microwave and radio photons, you might think that 2.725 K is the coldest you can ever get in nature. To experience something colder, you'd have to wait for the Universe to expand more, stretch the wavelengths of these photons, and cool down to an even lower temperature. This will happen, of course, in time. By time the Universe is twice as old as it is today -- in another 13.8 billion years -- the temperature will be just barely a single degree above absolute zero. But there's a place you can look, right now, that's colder than even the deepest depths of intergalactic space.

The Boomerang Nebula is a young planetary nebula and the coldest object found in the Universe so . [+] far. Image credit: ESA/NASA.

You don't even need to go anywhere special! This is the Boomerang Nebula, located just 5,000 light years away in our own galaxy. In 1980, when it was first observed from Australia, it looked like a two-lobed, asymmetrical nebula, and hence it was given the name "Boomerang" as a result. Better observations have shown us this nebula for what it really is: a preplanetary nebula, which is an intermediate stage in a dying, Sun-like star's life. All Sun-like stars will evolve into red giants and end their lives in a planetary nebula/white dwarf combination, where the outer layers are blown off and the central core contracts down to a hot, degenerate state. But in between the red giant and the planetary nebula phases, there's the preplanetary nebula phase.

The preplanetary nebula IRAS 20068+4051 is hotter than the Boomerang Nebula, but is still an . [+] intermediate phase between a red giant and a planetary nebula/white dwarf stage. Image credit: ESA/Hubble & NASA.

Before the internal temperature of the star heats up, but after the expulsion of the outer layers begins, we get a preplanetary nebula. Sometimes in a sphere, but more often in two, bipolar jets, the ejecta make their way out of the star's solar system and into the interstellar medium. This phase is short-lived: only a few thousand years. There are only a dozen or so stars that are found to be in this phase. But the Boomerang Nebula is special among them. Its gas gets expelled about ten times faster than normal: moving at about 164 km/s. It loses its mass at a higher rate than normal: about two Neptune's worth of material every year. And as a result of all of this, it's the coldest natural place in the known Universe, with some portions of the nebula coming in at just 0.5 K: half a degree above absolute zero.

A millimeter-wavelength view of the Boomerang Nebula. Image credit: . [+] NRAO/AUI/NSF/NASA/STScI/JPL-Caltech.

Every other planetary and preplanetary nebula is much, much hotter than this, but the physics underlying why is some of the simplest of all to understand. Inhale a deep breath, hold it for three seconds, and then let it out. You can do this two different ways, holding your hand about 6" (15 cm) away from your mouth both times.

  1. Exhale with your mouth wide open, and you'll feel the warm air gently blow onto your hand.
  2. Exhale with your lips puckered, making a tiny opening, and that same air feels cold.

In both cases, the air in your body has been warmed, and remains at that high temperature until just before it passes your lips. With your mouth wide open, it simply exits slowly, warming your hand slightly. But with only a tiny opening, the air expands rapidly -- what we call adiabatically in physics -- and cools as it does so.

Exhaling forcefully with your mouth open very, very slightly will cause the air to cool extremely . [+] quickly. Image credit: Pezibear of Pixabay, via https://pixabay.com/p-1465521/?no_redirect.

The outer layers of the star that's birthing the Boomerang Nebula has all of these same conditions:

  • a large amount of hot matter,
  • being ejected incredibly rapidly,
  • from a tiny point (well, two points),
  • that has all the room it could ask for to expand and cool.

The amazing thing about the Boomerang Nebula is that it was predicted before it was found! Astronomer Raghvendra Sahai calculated that preplanetary nebulae with just the right conditions -- the ones outlined above -- could actually achieve a cooler temperature than anything else that naturally occurred in the Universe. Sahai was then part of the team in 1995 that made the critical long-wavelength observations that determined the temperature of the Boomerang Nebula, now known as the coldest natural place in the Universe.

A color-coded temperature map of the Boomerang Nebula and the areas around it. The blue areas, which . [+] have expanded the most, are the coolest and lowest in temperature. Image credit: NASA / SPL.

As far as why the Boomerang Nebula is ejecting all this matter so quickly and in such a collimated fashion, that's a controversial and highly active area of research. So far, the Boomerang Nebula is the only preplanetary nebula whose temperature has dropped below that of the Big Bang's afterglow, but there's no way it's the only one that ever has. There's likely an even colder place out there. We just have to keep looking. And who knows? Perhaps, someday, our Sun will take the record for its own!


Water In Space: Does It Freeze Or Boil?

Water drops can exist inside the pressurized environment of the International Space Station, but . [+] send them outside the cabin into the vacuum of space, and they can be liquid no longer. Image credit: ESA/NASA, of Andre Kuipers.

If you brought liquid water into outer space, would it freeze or would it boil? The vacuum of space is awfully different from what we’re used to here on Earth. Where you stand now, surrounded by our atmosphere and relatively close to the Sun, the conditions are just right for liquid water to stably exist almost everywhere on our planet’s surface, whether it’s day or night.

The gravitational pull on the gases in our atmosphere cause a substantial surface pressure, giving . [+] rise to liquid oceans. Image credit: NASA Goddard Space Flight Center Image by Reto Stöckli, Terra Satellite / MODIS instrument.

But space is different in two extremely important ways: it’s cold (especially if you’re not in direct sunlight, or farther away from our star), and it’s the best pressureless vacuum we know of. While standard atmospheric pressure on Earth represents about 6 × 10^22 hydrogen atoms pushing down on every square meter at Earth’s surface, and while the best terrestrial vacuum chambers can get down to about one trillionth of that, interstellar space has a pressure that’s millions or even billions of times smaller than that!

From hundreds of miles up, the atmospheric pressure is some 10^18 times less than on Earth's . [+] surface. Even farther away, the pressure drops still further. Image credit: NASA.

In other words, there’s an incredible drop in both temperature and pressure when it comes to the depths of outer space as compared to what we have here on Earth. And yet, that’s what makes this question all the more troublesome. You see, if you take liquid water and you place it into an environment where the temperature cools to below freezing, it will form ice crystals in very, very short order.

The formation and growth of a snowflake, a particular configuration of ice crystal. Image credit: . [+] Vyacheslav Ivanov, from his video at Vimeo: http://vimeo.com/87342468.

Well, space is really, really cold. If we talk about going to interstellar space, far away (or shadowed) from any stars, the only temperature comes from the leftover glow from the Big Bang: the Cosmic Microwave Background. The temperature of this sea of radiation is only 2.7 Kelvin, which is cold enough to freeze hydrogen solid, much less water. So, if you take water into space, it should freeze, right?

Ice crystals forming in the wild on Earth's surface. Image credit: public domain photo by Pixabay . [+] user ChristopherPluta.

Not so fast! Because if you take liquid water and you drop the pressure in the environment around it, it boils. You might be familiar with the fact that water boils at a lower temperature at high altitudes this is because there’s less atmosphere above you, and hence the pressure is lower. We can find an even more severe example of this effect, however, if we put liquid water in a vacuum chamber, and then rapidly evacuate the air. What happens to the water?

It boils, and it boils quite violently at that! The reason for this is that water, in its liquid phase, requires both a certain range of pressure and a certain range of temperatures. If you start with liquid water at a given fixed temperature, a low enough pressure will cause the water to immediately boil.

In the liquid phase, dropping the pressure significantly can result in a solid (ice) or a gas (water . [+] vapor), depending on what the temperature is and how rapidly the transition occurs. Image credit: wikimedia commons user Matthieumarechal.

But on that first hand, again, if you start with liquid water at a given, fixed pressure, and you lower the temperature, that will cause the water to immediately freeze! When we talk about putting liquid water in the vacuum of space, we’re talking about doing both things simultaneously: taking water from a temperature/pressure combination where it’s stably a liquid and moving it to a lower pressure, something that makes it want to boil, and moving it to a lower temperature, something that makes it want to freeze.

You can bring liquid water to space (aboard, say, the international space station) where it can be kept in Earth-like conditions: at a stable temperature and pressure.

But when you put liquid water in space — where it can no longer remain as a liquid — which one of these two things happens? Does it freeze or boil? The surprising answer is it does both: first it boils and then it freezes! We know this because this is what used to happen when astronauts felt the call of nature while in space. According to the astronauts who’ve seen it for themselves:

When the astronauts take a leak while on a mission and expel the result into space, it boils violently. The vapor then passes immediately into the solid state (a process known as desublimation), and you end up with a cloud of very fine crystals of frozen urine.

There’s a compelling physical reason for this: the high specific heat of water.

The specific heats of various materials, elements and compounds. Note that liquid water has one of . [+] the highest heat capacities of all. Image credit: screenshot from the Wikipedia page for Heat Capacity, via https://www.youtube.com/watch?v=ntQ7qGilqZE.

It’s incredibly difficult to change the temperature of water rapidly, because even though the temperature gradient is huge between the water and interstellar space, water holds heat incredibly well. Furthermore, because of surface tension, water tends to remain in spherical shapes in space (as you saw above), which actually minimize the amount of surface area it has to exchange heat with its subzero environment. So the freezing process would be incredibly slow, unless there were some way to expose every water molecule individually to the vacuum of space itself. But there’s no such constraint on the pressure it’s effectively zero outside of the water, and so the boiling can take place immediately, plunging the water into its gaseous (water vapor) phase!

But when that water boils, remember how much more volume gas takes up than liquid, and how much farther apart the molecules get. This means that immediately after the water boils, this water vapor — now at effectively zero pressure — can cool very rapidly! We can see this on the phase diagram for water.

A detailed phase diagram for water, showing the different solid (ice) states, the liquid state and . [+] the vapor (gas) states, and the conditions under which they occur. Image credit: Wikimedia commons user Cmglee.

Once you get below about 210 K, you’re going to enter the solid phase for water — ice — no matter what your pressure is. So that’s what happens: first the water boils, and then the very fine mist that it boils away into freezes, giving rise to a tenuous, fine network of ice crystals. Believe it or not, we have an analogy for that here on Earth! On a very, very cold day (it has to be about -30° or lower for this to work), take a pot of some just-boiling water and throw it up (away from your face) into the air.

The quick reduction in pressure (going from having water on top of it to just air) will cause a rapid boil, and then the quick action of the extremely cold air on the water vapor will cause the formation of frozen crystals: snow!

Throwing boiling water into the air on Earth's surface, when it's cold enough, will result in the . [+] creation of snow, as the exposure of many small surfaces (drops and droplets) to the subzero temperatures result in the rapid formation of tiny ice crystals. Image credit: Mark Whetu, in Siberia.

So does water boil or freeze when you bring it to space? Yes. Yes. it does.


CMEs and space weather

Because of their speed, their large magnetic field strength, and their often long-lived and strong southward magnetic field component, many fast CMEs are highly geoeffective that is, energy is transferred effectively between the solar wind and Earth’s magnetosphere through the process of magnetic reconnection—the same process responsible for the formation of CMEs. If the IMF or the magnetic field inside a CME has a strong southward component, it can efficiently couple with the northward-pointing geomagnetic field, releasing much energy, transferring the mass and momentum of the solar wind into the magnetosphere, and generating a large geomagnetic storm. The largest geomagnetic storm ever recorded, that of Sept. 2, 1859, had intense auroral displays as far south as the tropics. On the previous day, astronomer Richard Carrington of the Royal Greenwich Observatory had made the first observations of a white-light solar flare, a bright spot suddenly appearing on the Sun. Carrington noted the coincidence (but did not claim a direct connection) between the auroras and the solar flare, thus prefiguring the discipline of space weather research.

It is now thought that the active region on the Sun that produced the white-light flare also produced a fast CME, which subsequently produced the geomagnetic storm. The energy of a CME depends on its velocity CMEs are launched with a wide variety of speeds, from less than 10 km (6 miles) per second to more than 2,000 km (1,200 miles) per second. Fast CMEs are those that travel faster than the background solar wind (which has an average speed of about 400 km [240 miles] per second). Although CMEs are often associated with solar flares, the two can occur independently. Both flares and CMEs are thought to be manifestations of the rearrangement of the solar magnetic field through the mechanism of magnetic reconnection. The energy carried in a fast CME is approximately the same as that released in a solar flare.