# Could a rocky rogue planet get trapped in the orbit between Earth and Mars?

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I know it's extremely unlikely a rogue planet passing by there, and I know the size of rocky planets can vary a lot (IIRC there is a rocky planet 5 times the size of Earth) but in any hypothetical case, could a rogue planet be trapped in any part of the orbit between Earth and Mars? If so, which are the possible effects it could have over Earth and Mars? In which cases would they be expelled from the solar system?

It is exceptionally unlikely.

Imagine that there was a planet already there. What could cause it to suddenly escape from the solar system? It would have to be a massive event, such as a second passing rogue planet catapulting it out of orbit.

Running time backwards, for a rogue planet to be captured and neatly end up orbiting between Mars and Earth would require an unbelievably unlikely sequence of events, such as

two rogue planets happen to pass between Earth and Mars at the same time and the interaction between the two results in a transfer of energy and momentum, which (by lucky chance) leaves one of the planets in a nearly circular orbit, (while the other escapes)".

Given how big space is, and in consequence, how rarely a rogue planet enters the inner solar system, this would make the above sequence of events practically impossible.

In this unbelievable scenario, the effects on Earth and Mars would depend on how closely the new planet passes. If we are close enough for significant effects on the planet, we are in a great deal of danger.

## Exo-Titans: why the moons of rogue planets could surprise us with alien life

The search for life on exoplanets takes a fairly conservative approach. It focuses on life that is similar to that of Earth.

The search for life on exoplanets takes a fairly conservative approach. It focuses on life that is similar to that of Earth.

Sure, it’s quite possible that life comes in many exotic forms, and scientists have speculated about all the strange forms life might take, but the simple fact is that Earth life is the only form we currently understand. So most research focuses on life forms that, like us, are carbon-based with biology that relies on liquid water.

But even with that narrow view, life could still be hiding in places we don’t expect.

Since terrestrial life depends on liquid water, the search for life on exoplanets focuses on those within the circumstellar habitable zone (CHZ) surrounding stars. That is, not too close nor too distant so that liquid water could exist on a rocky planet.

For our solar system that’s roughly between the orbits of Venus and Mars. Most of the exoplanets meeting that criteria are super-Earths that closely orbit small red dwarf stars, since red dwarfs make up about 75% of the stars in our galaxy, and super-Earths are the most common terrestrial exoplanet.

One of the surprising discoveries about exoplanets is that Jupiter-sized planets often orbit close to their stars. These “hot Jupiters” aren’t likely to have life, but they could have moons that are as warm and wet as Earth.

And it turns out that large gas planets don’t even have to orbit close to their star to have moons with liquid water. We know, for example, that the Jovian moon of Ganymede has a water ocean beneath its icy surface. Europa is known to have more water than Earth, and even Saturn’s small moon Enceladus has liquid water.

What’s interesting about these examples is that the presence of liquid water on these moons is due not to the heat of the Sun, but rather to thermal heating due to the gravitational tug of their planet. Of course, this raises an interesting question. If moons of Jupiter and Saturn can have liquid water, what about the moons of Jupiter-like exoplanets that don’t even orbit a star?

That is the question examined in a recent article in the International Journal of Astrobiology. What’s interesting about this study is that it’s not simply asking whether an exomoon could stay geologically active enough to have liquid water. The answer to that is clearly yes.

Instead, this work looks at how potentially habitable exomoons might form, and whether they could maintain enough liquid water long enough for primordial life to evolve.

For example, for moons within a stellar system, a primary driver for the chemical evolution of the moon would be the light and heat of the star. But for moons of rogue planets, a primary influence would be cosmic rays. This, combined with tidal heating, would drive the evolution of a moon’s atmosphere over time.

To see the effects of these differences, the team models an Earth-mass moon orbiting a Jupiter-mass rogue planet. They found that with some reasonable assumptions about chemical composition and orbital stability, a rogue exomoon could maintain liquid water on its surface. Much less than that of Earth, but plenty enough to allow for life to arise and evolve in a reasonable timescale.

It’s important to note that this model focused on exomoons with a rich atmosphere. If these habitable exomoons exist, we might be able to study their atmospheres through infrared and radio astronomy. So the first planet to show evidence of extraterrestrial life might be a rogue one.

This article was originally published on Universe Today by Brian Koberlein. Read the original article here.

## One swift kick

Gravity can be a tricky thing. One moment, it's holding a planet in orbit around a star, safely chained to that life-giving warmth for billions of years. The next, that very same gravity is sending the planet hurtling into the depths of interstellar space, doomed to wander the frozen wastelands of our galaxy, with any life on that planet quickly and permanently erased.

Gravity is so tricky because it's actually rather complex. When there are just two objects — say, a massive star and a single little planet — the math is easy to work out. Once a planet finds itself in a stable orbit, it will remain in place for billions upon billions of years without deviation, the regular rhythms of its motion repeating like the gears of a great clockwork mechanism.

But throw a third object into the mix? Anything goes — chaos. As in, literal chaos. The problem of trying to predict the motion of three objects interacting through gravity has been notorious for centuries, with intellectual heavyweights through the ages trying to come up with a solution and failing. The problem is that with three objects, any little deviation or shift can lead to massive changes in a surprisingly short amount of time.

In other words, what looks calm, cool and collected one moment — say, the fact that the Earth has orbited the sun placidly for billions of years — can become dangerously unstable the next.

But so far, so good, right? The rest of the planets in the solar system are relatively small, and while they do tweak and affect the Earth's orbit in subtle ways, they don't cause outright havoc and general destabilization. Things will be just fine for billions of years to come, as long as nothing massive — say, a passing star — comes close.

## How do planets go rogue?

These planets used to have the behavior of the normal planet before becoming a rogue if they belong to any star system. Then there is a question that “how are rogue planets formed”? Scientists do not know much about how exactly these planets formed, but they have some possible theories that might be the reason for the formation of a rogue planet.

#### ⇒ Planet ejected from a solar system

Usually, planets orbit their sun because they are gravitationally bound in the solar system. But sometimes due to any reason, they got expelled out from the solar system. The disturbance in the gravitational force is the most supported reason by the scientists to convert into a rogue planet.

Gravitational force may be disturbed when two planets approached each other near to the sun. In this case, sometimes the sun attracts one planet, whereas the second planet gets ejected out with high velocity. The velocity of the ejected planet is so high that it becomes free from the gravitational force of the sun. That’s how a planet becomes a rogue planet or unbound planet.

#### ⇒ A failed star explosion

When the core of a huge star explodes it formed a supernova and the explosion of the supernova emits high energy in the whole galaxy. But sometimes the explosion of a star is quite the opposite like they gently explode and disappears. This gentle explosion phenomenon of the star is called unnova.

In this case, the planets of that star system become orphans and they do not have any star or sun to orbit around. So the gravitational system of the planet gets disturbed and they start wandering in the galaxy. That’s how a rogue planet or wandering planet formed.

#### ⇒ Failed proper star formation

Many astronomers believe that rogue planets are formed in the same way as stars have formed and these planets are the case of failed star formation. Proper formation of a star takes millions of years but in some cases the available gas and dust to form a star get finished, then it is called a failed star. The failed star can also be known as a rogue planet if it does not have enough temperature like a proper star.

## Rogue planets could outnumber the stars

An artist’s rendering of the Nancy Grace Roman Telescope.
Graphic courtesy NASA.

An upcoming NASA mission could find that there are more rogue planets – planets that float in space without orbiting a sun – than there are stars in the Milky Way, a new study theorizes.

“This gives us a window into these worlds that we would otherwise not have,” said Samson Johnson, an astronomy graduate student at The Ohio State University and lead author of the study. “Imagine our little rocky planet just floating freely in space – that’s what this mission will help us find.”

The study was published today, Friday, Aug. 21, in The Astronomical Journal.

The study calculated that NASA’s upcoming Nancy Grace Roman Space Telescope could find hundreds of rogue planets in the Milky Way. Identifying those planets, Johnson said, will help scientists infer the total number of rogue planets in our galaxy. Rogue, or free-floating, planets are isolated objects that have masses similar to that of planets. The origin of such objects is unknown, but one possibility is they were previously bound to a host star.

“The universe could be teeming with rogue planets and we wouldn’t even know it,” said Scott Gaudi, a professor of astronomy and distinguished university scholar at Ohio State and a co-author of the paper. “We would never find out without undertaking a thorough, space-based microlensing survey like Roman is going to do.”

The Roman telescope, named for NASA’s first chief astronomer who was also known as the “mother” of the Hubble telescope, will attempt to build the census of rogue planets, which could, Johnson said, help scientists understand how those planets form. Roman will also have other objectives, including searching for planets that do orbit stars in our galaxy.

That process is not well-understood, though astronomers know that it is messy. Rogue planets could form in the gaseous disks around young stars, similar to those planets still bound to their host stars. After formation, they could later be ejected through interactions with other planets in the system, or even fly-by events by other stars.

Or they could form when dust and gas swirl together, similar to the way stars form.

The Roman telescope, Johnson said, is designed not only to locate free-floating planets in the Milky Way, but to test the theories and models that predict how these planets formed.

Johnson’s study found that this mission is likely to be 10 times more sensitive to these objects than existing efforts, which for now are based on telescopes tethered to the Earth’s surface. It will focus on planets in the Milky Way, between our sun and the center of our galaxy, covering some 24,000 light years.

“There have been several rogue planets discovered, but to actually get a complete picture, our best bet is something like Roman,” he said. “This is a totally new frontier.”

Rogue planets have historically been difficult to detect. Astronomers discovered planets outside Earth’s solar system in the 1990s. Those planets, called exoplanets, range from extremely hot balls of gas to rocky, dusty worlds. Many of them circle their own stars, the way Earth circles the sun.

But it is likely that a number of them do not. And though astronomers have theories about how rogue planets form, no mission has studied those worlds in the detail that Roman will.

The mission, which is scheduled to launch in the next five years, will search for rogue planets using a technique called gravitational microlensing. That technique relies on the gravity of stars and planets to bend and magnify the light coming from stars that pass behind them from the telescope’s viewpoint.

This microlensing effect is connected to Albert Einstein’s Theory of General Relativity and allows a telescope to find planets thousands of light-years away from Earth—much farther than other planet-detecting techniques.

But because microlensing works only when the gravity of a planet or star bends and magnifies the light from another star, the effect from any given planet or star is only visible for a short time once every few million years. And because rogue planets are situated in space on their own, without a nearby star, the telescope must be highly sensitive in order to detect that magnification.

The study published today estimates that this mission will be able to identify rogue planets that are the mass of Mars or larger. Mars is the second-smallest planet in our solar system and is just a little bigger than half the size of Earth.

Johnson said these planets are not likely to support life. “They would probably be extremely cold, because they have no star,” he said. (Other research missions involving Ohio State astronomers will search for exoplanets that could host life.)

But studying them will help scientists understand more about how all planets form, he said.

“If we find a lot of low-mass rogue planets, we’ll know that as stars form planets, they’re probably ejecting a bunch of other stuff out into the galaxy,” he said. “This helps us get a handle on the formation pathway of planets in general.”

## Rogue One

The search for life on exoplanets takes a fairly conservative approach. It focuses on life that is similar to that of Earth. Sure, it&rsquos quite possible that life comes in many exotic forms, and scientists have speculated about all the strange forms life might take, but the simple fact is that earthlife is the only form we currently understand. So most research focuses on life forms that, like us, are carbon based with a biology that relies on liquid water. But even with that narrow view, life could still be hiding in places we don&rsquot expect.

Since terrestrial life depends on liquid water, the search for life on exoplanets focuses on those within the circumstellar habitable zone (CHZ) surrounding stars. That is, not to close nor too distant, so that liquid water could exist on a rocky planet. For our solar system that&rsquos roughly between the orbits of Venus and Mars. Most of the exoplanets meeting that criteria are super-Earths that closely orbit small red dwarf stars, since red dwarfs make up about 75% of the stars in our galaxy, and super-Earths are the most common terrestrial exoplanet.

One of the surprising discoveries about exoplanets is that Jupiter-sized planets often orbit close to their stars. These &ldquohot-Jupiters&rdquo aren&rsquot likely to have life, but they could have moons that are as warm and wet as Earth.

/>PHL @ UPR Arecibo Known potentially habitable worlds as of 2020.

And it turns out that large gas planets don&rsquot even have to orbit close to their star to have moons with liquid water. We know, for example that the Jovian moon of Ganymede has a water ocean beneath its icy surface. Europa is known to have more water than Earth, and even Saturn&rsquos small moon Enceledus has liquid water. What&rsquos interesting about these examples is that the presence liquid water on these moons is due not to the heat of the Sun, but rather to thermal heating due to the gravitational tug of their planet. Of course, this raises an interesting question. If moons of Jupiter and Saturn can have liquid water, what about the moons of Jupiter-like exoplanets that don&rsquot even orbit a star?

/>Tommaso Grassi / LMU Illustration of a planet floating freely through the universe with a potentially habitable moon.

That is the question examined in a recent article in the International Journal of Astrobiology. 1 What&rsquos interesting about this study is that it&rsquos not simply asking whether an exomoon could stay geologically active enough to have liquid water. The answer to that is clearly yes. Instead, this work looks at how potentially habitable exomoons might form, and whether they could maintain enough liquid water long enough for primoridal life to evolve. For example, for moons within a stellar system, a primary driver for the chemical evolution of the moon would be the light and heat of the star. But for moons of rogue planets, a primary influence would be cosmic rays. This, combined with tidal heating would drive the evolution of a moon&rsquos atmosphere over time.

To see the effects of these differences, the team models an Earth-mass moon orbiting a Jupiter-mass rogue planet. They found that with some reasonable assumptions about chemical composition and orbital stability, a rogue exomoon could maintain liquid water on its surface. Much less than that of Earth, but plenty enough to allow for life to arise and evolve in a reasonable timescale.

It&rsquos important to not that this model focused on exomoons with a rich atmosphere. If these habitable exomoons exist, we might be able to study their atmospheres through infrared and radio astronomy. So the first planet to show evidence of extraterrestrial life might be a rogue one.

Patricio Javier Ávila, et al. &ldquoPresence of water on exomoons orbiting free-floating planets: a case study.&rdquo International Journal of Astrobiology FirstView (2021): 1-12. ↩︎

## Is this rogue planet capture process possible?

I have a prelude to a story which involves a rogue planet entering the solar system, However I am concerned as to its realism. All of this is supposed to be based on real physics and rules there's nothing special like magic, insane technology and hopefully I don't require adding anything special to make it realistic. Here's how it goes:

While searching for planet nine, scientists eventually detect something. However on closer analysis, this is no solar object. This is a rogue planet an ice giant with 1 major moon. Worse still, its trajectory takes it on a close flyby of Jupiter, which is expected to tear its moon (about 2/3 the mass of Earth) out of orbit and into a flyby trajectory of Earth! The object does so, and although it does not collide with the planet, it does irreparably alter Earths orbit, and Earth is expected to be inhospitable to humans in about a thousand years. Thankfully, this would-be species killer also offers refuge. It eventually settles into a stable orbit in the asteroid belt, capturing Ceres as a close moon and flinging the remaining asteroids all over the place. It also heats up due to an abundance of greenhouse gasses, and with a hot, active core (previously heated by tidal forces) for a magnetic field, Liquid water eventually melts and the planet becomes habitable. The planet (after thawing) has a breathable atmosphere, however it is also much thicker than Earths. Its surface gravity is about 5/7 Earths gravity and atmospheric pressure is about 6 Earth Atmospheres.

Meanwhile the ice giant is flung into an elliptical orbit, with its perihelion at around Mars's orbit, and its Aphelion just outside of Sedna's perihelion. Eventually though, through interacting with the other giant planets, settles into a metastable orbit between Jupiter and Saturn. Although expected to only last a few million years, this keeps it away from humanity in the meantime.

Not all is good, though. As the once rogue moon thaws in the embrace of Sols energy, something once frozen wakes up, and is not happy to see another species trying to take over their planet, regardless of its necessity to humanities survival.

NOTE: A lot of people seem to think the Ice Giant is the planet that becomes habitable. This is not true The MOON of the Ice Giant is what stabilizes in the asteroid belt and becomes habitable.

The story is, obviously, about the incoming war between Humanity, driven by the simple need to survive, and the aliens, driven by self defense. Here's a rundown of the aliens. If there's somthing that'd render humanities war completely hopeless or the survival of the aliens impossible, let me know as I'm concerned for that realism too:

The aliens have 300 years more advanced tech than humanity and survived the rogue phase by doing some alterations to their genetics so they could hibernate for the millions of years needed. They did the same alterations to important plants/animals in their ecology as well, specifically their own food chain. But most of the rest of life like bacteria and viruses died in the rogue phase, except for some arctic microbes and deep sea life, neither of which I think should pose much of a biological threat. I'll go into more detail of the match up later when I make the post asking if/how humanity would win.

## Rogue rocky planet found adrift in the Milky Way

Not all planets orbit stars. Some are instead “free-floating” rogues adrift in interstellar space after being ejected from their home systems. For decades astronomers have sought to study such elusive outcasts, hoping to find patterns in their size and number that could reveal otherwise hidden details of how planetary systems emerge and evolve.

Of the handful known so far, most free floaters have been massive gas giants, but now researchers may have found one small enough to be rocky—smaller even than Earth. If its rogue status is confirmed, the roughly Mars-to-Earth-mass object would be the most diminutive free-floating planet ever seen. Yet finding such small worlds could soon become routine, thanks to NASA’s upcoming Nancy Grace Roman Space Telescope, set to launch in the mid-2020s.

Most planet-hunting methods rely on observing subtle changes in a star’s light to discern any orbiting companions. But free-floating worlds, of course, have no star. Instead astronomers use a quirk of Einstein’s general theory of relativity to locate these lost planets: All massive objects warp spacetime around themselves, similar to how a bowling ball stretches a rubber sheet, and can act as lenses to magnify far-distant sources. When a “lensing” foreground planet is properly aligned with a background star, it amplifies that star’s light, causing a slight brightening. This technique is known as microlensing, and astronomers first pioneered it to find black holes.

Of the approximately 100 worlds found to date by microlensing, only four have been identified as free-floating. All the rest are planets that spin around their stars on orbits that are stretched out so long that they typically elude detection through other standard planet-hunting techniques. It is possible that the newfound wee world, known as OGLE-2016-BLG-1928, could be attached to a star. But if so, its orbit would place it at least eight times as far from its stellar host as the Earth is from the sun. Confirming the planet’s likely free-floating status will require a few more years—time enough for any potential parent star, should it exist, to shift its position so that its light can be separated from that of the background star.

“It’s really a very exciting result,” says Andrew Gould, an astronomer at the Ohio State University and an author of the preprint paper describing the result. That study, which was led by Przemek Mróz of the California Institute of Technology, has been submitted to Astrophysical Journal Letters, where it is currently under review. “It’s a huge milestone to get this planet,” Gould adds.

“This is a very robust result and almost certainly a low-mass planet,” says astronomer Scott Gaudi of Ohio State, who is leading the science team working to determine the best observing strategy for NASA’s Roman telescope and was not part of the group that found the new world. “This gives us the first little peek at the likely distribution of a population of Earth-mass planets in the galaxy,” he says.

At the “Hairy Edge”

Most planets form from the gas and dust left over after a star is born. Under the leading planetary formation model, called core accretion, the gas and dust gradually and incrementally combine to form larger and larger pieces that eventually coalesce into planets. A competing theory, disk instability, instead proposes that small segments of the disk rapidly collapse to form planets, and it favors the creation of larger worlds over smaller rocky ones.

Not all planets in a family get along. Gas giants can act as bullies, flinging their smaller siblings into elongated orbits or tossing them out of their system completely. These ejected worlds may continue to fly through space on their own as free-floating planets.

The Optical Gravitational Lensing Experiment (OGLE) has been scanning the skies since 1992 for the faint stellar flickers caused by microlensing events. But the new world was not spotted until Mróz and his colleagues reviewed some of OGLE’s archival data. By combining OGLE’s results with contemporaneous observations from the Korea Microlensing Telescope Network, as well as data from the European Space Agency’s Milky Way–mapping Gaia satellite, the team was able to better estimate properties useful for gauging the putative free-floating planet’s mass, such as the distance between the world and the background star. Mróz and his colleagues ultimately pegged the world’s mass at somewhere between that of Mars and Earth—making it one of the smallest objects ever found by microlensing.

“It’s really at the hairy edge of what we can do,” Gaudi says.

Probing Planetary Formation

This discovery hints that rocky worlds are common in the space between stars. Detecting something like this at the limits of astronomers’ current capabilities suggests OGLE was either incredibly lucky or that small free-floating planets wander the Milky Way in astronomical abundance.

The discovery of a single free-floating terrestrial planet demonstrates that such objects do, in fact, exist, whereas before they were only theorized. And as more low-mass drifters are found, they can help scientists narrow down how worlds are born. Core accretion models suggest planets should form in bunches, while a star might form a single world under disk instability. Because of their isolation, single-world systems would have no planets to eject. If astronomers find very few free-floating worlds as technology improves, disk instability might gain stronger support as the dominant mode of planet formation. At the same time, finding terrestrial worlds drifting through deep space provides more support for the core accretion model. “It’s very difficult to form such low-mass planets” under disk instability says Wei Zhu, a research associate at the Canadian Institute for Theoretical Astrophysics, who was not part of the new discovery. The newfound drifter instead provides strong support for the core accretion model. “That’s a good sign,” he says.

But ejection caused by planetary interactions is not the only way to wind up with worlds flying through stars, which theorists will have to take into account in their studies. Most stars form in clusters, surrounded by their own stellar siblings, and they might be much better at sharing than planets are. Worlds in the outskirts of their system could be pulled away completely by the gravity of a passing star, either joining that other star’s collection of planets or being tossed aside into space. Some castaway worlds may even find themselves bouncing from star to star, attaching to and being stripped from one sun after another. “They’re basically Ping-Pong planets,” says Susanne Pfalzner, an astronomer at the Jülich Research Center in Germany, who was not part of Mróz’s team.

Beyond its potential implications for planet-formation models, the newfound rogue planet is already having an effect on astronomers’ plans for future missions. According to Gaudi, it strengthens the case for changing Roman’s survey strategy. The OGLE observations only utilized a single light filter, but two different filters can help to disentangle the source star more easily, making stronger measurements of the stellar properties that help determine the mass of the free-floating planet. Roman originally planned to focus most of its observations on a single filter, only occasionally switching to a second, but Gaudi says the new study is making the planning team reinvestigate whether more two-filter observations would be worth the reduction in data quality that would occur.

Regardless, current best-guess projections suggest Roman should reveal more than 200 free-floating Mars-sized planets—enough to potentially determine whether most are products of planetary interactions or of stellar encounters in clusters, Zhu says. In contrast, Gould is skeptical that Roman will detect sufficient numbers of small worlds to robustly discern between these two possibilities, but he remains sanguine about the future observatory’s transformative effects.

“Roman will find more free-floating planets at a higher rate than we are finding today,” he says. “It’s going to be a huge leap.”

## Invisible rogue planets without stars? NASA’s new space telescope could find hundreds of them

The Nancy Grace Roman Space Telescope, NASA’s upcoming observatory expected to launch in the mid-2020s, could reveal a multitude of rogue planets that don’t orbit stars in our Milky Way galaxy, according to new research.

These exoplanets, or planets located outside of our solar system, move through the galaxy on their own and aren’t locked in orbits around stars that way Earth orbits the sun. Understanding these rogue planets could shed more light on the formation, evolution and disruption of planetary systems.

These rogue planets are difficult to detect and scientists have only found a few. But the Roman Space Telescope’s capabilities will allow it to find and characterize these roaming nomad planets.

The study published Friday in the Astronomical Journal.

“As our view of the universe has expanded, we’ve realized that our solar system may be unusual,” said Samson Johnson, study author and graduate student at The Ohio State University, in a statement. “Roman will help us learn more about how we fit in the cosmic scheme of things by studying rogue planets. Imagine our little rocky planet just floating freely in space — that’s what this mission will help us find.”

The telescope, named in honor of the agency’s first chief of astronomy, is equipped with a powerful 2.4-meter mirror that will allow it to search for exoplanets. The telescope will stare at large swaths of the sky and watch for gravitational microlensing events, where a planet and the star it orbits pass in front of a background star.

Microlensing occurs when the presence of something massive can actually warp space-time, like black holes, but it can also occur around planets.

For instance, if a rogue planet is in alignment with a distant star, the light from that star will essentially bend around the planet, resulting in a magnifying effect. Researchers can use the changes in light around the planet to measure the planet’s mass.

“The microlensing signal from a rogue planet only lasts between a few hours and a couple of days and then is gone forever,” said Matthew Penny, study coauthor and an assistant professor of physics and astronomy at Louisiana State University in Baton Rouge, in a statement. “This makes them difficult to observe from Earth, even with multiple telescopes. Roman is a game-changer for rogue planet searches.”

Given the fact that rogue planets don’t emit light like stars, or even enough heat to be visible in infrared light, these otherwise invisible worlds will be visible through the Roman Telescope’s observations of microlensing events.

### Understanding rogue planets

The telescope’s field of view that is a hundred times greater than Hubble’s infrared instrument, meaning the telescope can observe more of the sky in less time, the agency said. It will also allow for high-contrast imaging of individual nearby exoplanets.

The Roman Space Telescope will measure light from a billion galaxies and seek to provide data that could answer key questions about how common planetary arrangements are to our own solar system, as well as how many planets may be able to harbor life.

It also has the ability to find rogue planets as small as Mars, which is slightly bigger than half the size of Earth.

So how do rogue planets form?

Planet birth itself is a violent, erratic process. Gas and dust in disks around young stars clump together and gradually grow in size to form planets. But collisions between objects on grander scales, or even coming too close to another planet in orbit around the star, or the star itself, can kick the planet out of its system.

And then the planet is on its own — it’s gone rogue.

It’s also possible that lonely planets can form on their own in isolated clouds of gas and dust.

The Roman Telescope will help researchers determine how these planets form by providing information about how many there are as well as their masses — which could help indicate their origin story.

Recent research using estimates from ground-based telescopes suggests that the Roman Telescope could find hundreds of rogue planets, helping scientists understand how common they are in the Milky Way. The telescope’s discoveries could reveal that there are actually more rogue planets than there are stars in our galaxy, according to the study.

The Roman Telescope will be 10 times more sensitive to rogue planet detection than other telescopes and it will search for them across 24,000 light-years between our sun and the center of the galaxy.

“The universe could be teeming with rogue planets and we wouldn’t even know it,” said Scott Gaudi, study coauthor and a professor of astronomy at The Ohio State University, in a statement. “We would never find out without undertaking a thorough, space-based microlensing survey like Roman is going to do.”

## Contents

All terrestrial planets in the Solar System have the same basic structure, such as a central metallic core (mostly iron) with a surrounding silicate mantle. The Earth's Moon is similar, but has a much smaller iron core other natural satellites, such as Io, Europa, and Titan, also have internal structures similar to that of terrestrial planets.

Terrestrial planets can have surface structures such as canyons, craters, mountains, volcanoes, and others, depending on the presence of an erosive liquid and / or tectonic activity.

Terrestrial planets have secondary atmospheres, generated by volcanic out-gassing or from comet impact debris. This contrasts with the outer, giant planets, whose atmospheres are primary primary atmospheres were captured directly from the original solar nebula. [4]

The Solar System has four terrestrial planets: Mercury, Venus, Earth and Mars. Only one terrestrial planet, Earth, has an active hydrosphere.

During the formation of the Solar System, there were many terrestrial planetesimals and proto-planets, but most merged with or were ejected by the four terrestrial planets, leaving only a few such as 4 Vesta to survive.

Dwarf planets, such as Ceres, Pluto and Eris, are similar to terrestrial planets in that they have a solid surface, but are composed of ice and rock rather than of rock and metal. Some small Solar System bodies such as Vesta are quite rocky, or in the case of 16 Psyche even metallic like Mercury, while others such as 2 Pallas are icier.

Most planetary-mass moons are ice-rock or even primarily ice. The three exceptions are Earth's moon, which has a composition much like the Earth's mantle, Jupiter's Io, which is silicate and volcanic, and Jupiter's Europa, which is believed to have an active hydrosphere.

### Density trends Edit

The uncompressed density of a terrestrial planet is the average density its materials would have at zero pressure. A greater uncompressed density indicates greater metal content. Uncompressed density differs from the true average density (also often called "bulk" density) because compression within planet cores increases their density the average density depends on planet size, temperature distribution and material stiffness as well as composition.

Densities of the terrestrial planets
Object Density (g·cm −3 ) Semi-major axis (AU)
Mean Uncompressed
Mercury 5.4 5.3 0.39
Venus 5.2 4.4 0.72
Earth 5.5 4.4 1.0
Mars 3.9 3.8 1.52

The uncompressed density of terrestrial planets trends towards lower values as the distance from the Sun increases. For example, the rocky minor planet Vesta orbiting outside of Mars at 2.36 AU is less dense than Mars, at 3.5 g·cm −3 , and icier Pallas, orbiting at 2.77 AU, is less dense still at 2.9 g·cm −3 .

Earth's Moon has a density of 3.3 g·cm −3 and Jupiter's satellites Io and Europa are 3.5 and 3.0 g·cm −3 other large satellites are icier typically have densities less than 2 g·cm −3 . [5] [6] The dwarf planets Ceres, Pluto and Eris have densities of 2.2, 1.9 and 2.5 g·cm −3 , respectively. (At one point Ceres was sometimes distinguished as a 'terrestrial dwarf', vs Pluto as an 'ice dwarf', but the distinction is no longer tenable. It now appears that Ceres formed in the outer Solar System and is itself quite icy.)

Calculations to estimate uncompressed density inherently require a model of the planet's structure. Where there have been landers or multiple orbiting spacecraft, these models are constrained by seismological data and also moment of inertia data derived from the spacecraft orbits. Where such data is not available, uncertainties are inevitably higher. [7] It is unknown whether extrasolar terrestrial planets in general will show to follow this trend.

Most of the planets discovered outside the Solar System are giant planets, because they are more easily detectable. [8] [9] [10] But since 2005, hundreds of potentially terrestrial extrasolar planets have also been found, with several being confirmed as terrestrial. Most of these are super-Earths, i.e. planets with masses between Earth's and Neptune's super-Earths may be gas planets or terrestrial, depending on their mass and other parameters.

During the early 1990s, the first extrasolar planets were discovered orbiting the pulsar PSR B1257+12, with masses of 0.02, 4.3, and 3.9 times that of Earth's, by pulsar timing.

When 51 Pegasi b, the first planet found around a star still undergoing fusion, was discovered, many astronomers assumed it to be a gigantic terrestrial, [ citation needed ] because it was assumed no gas giant could exist as close to its star (0.052 AU) as 51 Pegasi b did. It was later found to be a gas giant.

In 2005, the first planets orbiting a main-sequence star and which show signs of being terrestrial planets, were found: Gliese 876 d and OGLE-2005-BLG-390Lb. Gliese 876 d orbits the red dwarf Gliese 876, 15 light years from Earth, and has a mass seven to nine times that of Earth and an orbital period of just two Earth days. OGLE-2005-BLG-390Lb has about 5.5 times the mass of Earth, orbits a star about 21,000 light years away in the constellation Scorpius. From 2007 to 2010, three (possibly four) potential terrestrial planets were found orbiting within the Gliese 581 planetary system. The smallest, Gliese 581e, is only about 1.9 Earth masses, [11] but orbits very close to the star. [12] Two others, Gliese 581c and Gliese 581d, as well as a disputed planet, Gliese 581g, are more-massive super-Earths orbiting in or close to the habitable zone of the star, so they could potentially be habitable, with Earth-like temperatures.

Another possibly terrestrial planet, HD 85512 b, was discovered in 2011 it has at least 3.6 times the mass of Earth. [13] The radius and composition of all these planets are unknown.

The first confirmed terrestrial exoplanet, Kepler-10b, was found in 2011 by the Kepler Mission, specifically designed to discover Earth-size planets around other stars using the transit method. [14]

In the same year, the Kepler Space Observatory Mission team released a list of 1235 extrasolar planet candidates, including six that are "Earth-size" or "super-Earth-size" (i.e. they have a radius less than 2 Earth radii) [15] and in the habitable zone of their star. [16] Since then, Kepler has discovered hundreds of planets ranging from Moon-sized to super-Earths, with many more candidates in this size range (see image).

In September 2020, astronomers using microlensing techniques reported the detection, for the first time, of an earth-mass rogue planet (named OGLE-2016-BLG-1928) unbounded by any star, and free floating in the Milky Way galaxy. [17] [18] [19]

### List of terrestrial exoplanets Edit

The following exoplanets have a density of at least 5 g/cm 3 and a mass below Neptune's and are thus very likely terrestrial:

The Neptune-mass planet Kepler-10c also has a density >5 g/cm 3 and is thus very likely terrestrial.

### Frequency Edit

In 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth- and super-Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way. [20] [21] [22] 11 billion of these estimated planets may be orbiting Sun-like stars. [23] The nearest such planet may be 12 light-years away, according to the scientists. [20] [21] However, this does not give estimates for the number of extrasolar terrestrial planets, because there are planets as small as Earth that have been shown to be gas planets (see Kepler-138d). [24]

Several possible classifications for terrestrial planets have been proposed: [25]

## 8 Answers 8

I wouldn't think Earth has much chance of starting much of a colony there with current technology, though I think we could make a ship that could get there. (So depends on what kind of colony counts - in The Martian, growing potatoes technically counts, so yes we could probably do that. But we could do that in space, too.) We might be able to get some people there, but long-term survival would be difficult.

Seems to me the question becomes whether it's liable to be any easier than staying alive someplace else, like Mars.

The main factor in answering that, would be what the future trajectory of this planet is. I'd start by trying to actually find what possible trajectories meet your criteria. Earth speed relative to the sun is about 30 km per second, so if this new planet continued at 50 km per second, and was not headed for the sun, but part of the orbit included the Earth's position, then it's orbit will be at a more oblique angle than earth is. Given that it's going to change Earth's orbit enough to have Earth crash into the sun, that means this planet's orbit is also going to change. To be realistic, I'd want to have an actual set of motions where the numbers make sense. Knowing the future orbit would give very important information about the future conditions of that planet, mainly for temperature. Its rotation would also be important.

I'd spend some time running orbital simulations to find out if there is anything set of movements I can find that would be anything like this. Eg it's a great excuse to go play with Universe Sandbox or such.

My first thought though is that I'm not coming up with any way that a planet could appear in a near-Earth orbit like that at such low relative speed, unless some sort of teleportation is involved. It also occurs to me that it's even harder for me to imagine any situation where we would not know the planet was coming for many years, not just one, again unless some sort of magic/unexplainable appearance from nowhere is involved.

Once the rogue planet is out of the solar system it won't get any sunlight making it incredibly difficult to live on.

Maybe you can set up some sort of habitat and rely on nuclear energy (give that the rogue planet has ample deposits of uranium), but with current technology that would be virtually impossible.

We have limited number of rockets available, we don't have any landers to take us to the surface, much less any ready habitats we can deploy. A viable colony will need at least a couple of hundred people to get enough genetic diversity. Finding that many qualified people, screening them, training them, making sure they form a cohesive unit takes time.

Now imagine all the equipment you'll need. You have to assume the worst possible conditions - temperatures near absolute zero, unbreathable atmosphere, the surface covered by miles ice.

The space station and the Amundsen–Scott South Pole Station are the two places that are most similar to the outpost you are suggesting, but those need to be resupplied every few months, they are nowhere near self reliant.

No. We'd all die.

One year is, at the very best, enough time to design and build a lander that could bring fewer than ten humans from Earth to land on a rocky planet with Earth like gravity and a thin atmosphere. With the relatively high gravity and little assistance from an atmosphere to make a landing, the ship needs to carry a lot of fuel to slow the descent. Getting a handful of people there is a monumental task, let alone getting thousands of people and the equipment to survive on a frozen world.

Hopefully they'd realize that any close approach that could eject the Earth into the Sun would 1) take a long time for the Earth to get there and be destroyed and 2) cause significant havoc on the object upsetting Earth's orbit, likely destroying any fledgling colony there.

The fact that the "calculations aren't yet precise enough to find out what will happen to the planet" is not a promising point in trying to move humanity there.

"Physicists calculate that it will destabilise Earth's orbit and send Earth heading straight into the sun. The calculations aren't yet precise enough to find out what will happen to the planet."

1)It only approaches within 10 million kilometers, about 30 times farther than the moon. There is no way that will destabilize the earth's orbit, since the worst-case gravitational pull on the earth will be about 1/9 that of the moon, and that will occur for a fairly short time due to the high velocity.

2) If the effect on the earth is known, the effect on the rogue is known. You can't have it both ways.

56 km/s). In reality, the orbit would most likely be quite elliptical. We can't really guess at the angle of approach, because 50 km/s at Earth's distance from the Sun is just way too low for a rogue planet - once you include "somebody put it there at that speed", there's not much you can estimate. And if it had a collision before reaching Earth, it would likely be partially molten - not very habitable. $endgroup$ &ndash Luaan Oct 29 '15 at 9:07

no. The rogue planet will exit the solar system an freeze. And I don't mean freeze like how Antarctica is frozen, I mean that it will approach absolute zero.

With current technology, we would not be able to create enough energy to keep the colony warm, never mind fed, watered and oxygenated.

If we had cold fusion reactors and also 100 years to plan the mission, then maybe.

Edit: I didn't think of geothermal warmth. So you want to build a thermal heat powerplant and giant hydroponics farm 1km under the surface? We could not even build that kind of colony on earth, given a 1 year time frame. Imagine then if every piece or necessary equipment then needs to be launched into space and landed of the other planet. We could not even provide the fuel to put it all up there.

A rogue planet will not get energy from Sun, so the colony would need to use nuclear energy to produce warmth and light as required.

Ordinary reactors use uranium that may not be easily available with reduced scale technology, but termonuclear reactors may need just water, or maybe tritium that could be purified from large amounts of water (assuming the planet has a frozen ocean with plenty of water available). Such devices are not used in production yet but they are under development.

If we get a small self-sustained colony, it may have much more time later to perfect the technologies.

Any colony based on current technology would only be habitable foe the period of time that the rogue remained in the habitable zone of our star. Once the rogue left that zone, the planet would likely rapidly become either too hot or too cold to remain habitable. This is assuming that the planet even had an atmosphere, and what you would consider "colonized" to mean.

Like other answers so far, I don't think that we have any chance of establishing a colony on that planet. I would like to add another reason, however, for why this is not possible with current technology.

You state that the planet is a year away and moving at 50 km/s at a right angle to the solar system ecliptic, heading for us. This puts its current distance at about 10.5 AU from the ecliptic and presumably a very similar distance from the Earth.

Uranus' orbit around the sun has a semi-major axis (distance along the greatest diameter) of about 20.1 AU. Since Earth's distance from the sun is about 1 AU, this means that the rogue planet is currently about as far away from Earth as is Uranus at closest approach. (This isn't very far at all in astronomical terms, but it is still quite a distance.)

We don't have the ability to go to Uranus in any way that would allow us to establish a colony around those parts of the solar system. Heck, we can't even do it to Mars, which is practically next door in comparison.

But wait -- it gets worse! This rogue planet is moving toward our solar system at those same 50 km/s, to within rounding error. Excluding solar probes like the HELIOS probes, the fastest spacecraft that have been launched from Earth move at about 15-20 km/s relative to the sun. Let's be generous and call it an even 20 km/s. Let's also be very generous and say we could get to this velocity without spending a lot of time doing fancy gravity slingshots, which almost certainly would be required in practice. Let's also say that we put all that effort into getting a spacecraft moving toward the rogue planet. Forget about the specifics of the spacecraft, let's just get it on the quickest possible intersecting trajectory at 20 km/s relative to the sun.

The relative speed of the two are now on the order of 70 km/s. The rogue planet is approaching the ecliptic at 50 km/s, and our spacecraft is moving away from the ecliptic (and toward the rogue planet) at an additional 20 km/s relative to the ecliptic.

In order to survive landing, we need to bring the relative speed down to effectively zero. In other words, for landing, we need to somehow come up with a delta-v (velocity change) budget of 70 km/s.

The way rockets work is by bringing mass (fuel), which is pushed in one direction to cause a resultant velocity change in the other direction. (Newton's third law of motion.) This lowers the mass of the rocket, which means we need less mass the next instant for the same velocity change. Conversely, going backwards, we need to bring enough mass with us to apply the change in velocity not just to the rocket itself and its payload, but also to the remaining mass of the fuel. This is known as the tyranny of the rocket equation.

When Apollo went to the Moon, after the TLI burn (translunar injection, which raised the spacecraft's orbit such that it went from a low-Earth orbit into an orbit that intersected the Moon, whether or not in a free return manner depending on the specific mission), the spacecraft was moving at about 11 km/s relative to the Earth. For any significant payloads, this is about the best we have been able to do so far. Besides the fact that this would be needed on the outbound leg of the trip, this left the Apollo CSM with very little additional delta-v budget the LM had a bit to spare, for a soft landing on the Moon, but we are talking nowhere near the amounts that would be needed.

Even given maximum generosity and taking the velocity change from takeoff from ground to after TLI, your delta-v budget is now short only a measly 59 km/s. (In reality, it would be short a lot more.) Since lithobraking from even the slow and gentle 59 km/s to 0 km/s relative to the ground tends to be a bad idea, and because of the rocket equation's exponential nature, this is very bad news.

TLDR: Even if we could figure out a way to establish a colony that would be able to survive, given current technology, we have no realistic way of getting there in the first place.