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Super-Earths are ideal targets in the search for life


> If a super-Earth is ejected from its star system and has a dense atmosphere and watery surface, it could sustain life for tens of billions of years, far longer than life on Earth could persist before the sun dies.

What would be the energy source to sustain life on an ejected super-Earth? Radioactivity? Tidal forces from orbiting moons?


This seemed off the me also. Reading through the paper quoted in this sentence makes it clear that the sentence is just wrong. From [1]:

"The team found that planets 10 times the mass of the Earth, with an atmosphere 100 to 1000 times thicker than Earth’s, may be the most favorable for storing life for billions of years. But to do this, they must orbit the star at a distance that the orbit of Mars occupies in the Solar System. At such a potentially safe distance, the original atmospheres can act as greenhouse gases, absorbing infrared radiation, providing the necessary heat and pressure that can support life in oceans of liquid water."

So the planet is not ejected from the system, just pushed out so that instead of an orbit of days it is as far away as Mars is to our sun (1.5 AU). Gell-Mann Amnesia comes into play here.



Thanks for spotting that link.

Digging one link farther reveals the original article [2] which is more detailed and descriptive than the others. The original article explores super-Earths where the primordial H–He atmosphere is retained and traps enough heat to sustain liquid water, and includes simulations of “unbound” super-Earths that are ejected from their star systems. The mathematical model [3] incorporates the initial heat from planet formation and radiogenic heat but does not mention tidal forces.




The original article also includes this discussion of habitability:

Life on the type of planet described in this work would live under considerably different conditions than most life on Earth. The surface pressures in our results are on the order of 100–1,000bar, the pressure range of oceanic floors and trenches. There is no theoretical pressure limit on life, and some of the most extreme examples in Earth’s biosphere thrive at ~500bar. These habitats also receive a negligible amount of direct sunlight, and therefore photosynthesis would not be an optional mechanism to provide for metabolism. Chemoautotrophic life on Earth would be a more likely analogue to possible life on this type of planet.




Just to point that water is almost exactly 1000 times thicker than air Edit: 800 times if we have to be precise


I don’t think we’re exactly sure how much of the Earth’s heat is due to radioactive materials in the core or just left-over heat from its formation, but either way a super Earth should have more of both.


One of the early pieces of evidence for the existence of radioactivity had to do with the fact that the Earth’s core is way too hot to be billions of years old. Even if there were coal veins down there just burning slowly forever.


Yeah, I wondered about that as well. It must be radioactive and residual heat from the core.

I can’t imagine geothermal supporting as vibrant an ecosystem as photons pouring in everyday allow photosynthesis to do.


I suppose one cannot expect anything better from a site called singularity hub, but this post is disingenuous (or written by an actual hack) for multiple reasons. Aren’t the majority of planets we are discovering all orbiting red dwarfs, which can exhibit massive swings in luminosity and be very violent? Even the example quoted by the author which such a short radius seems one of them. Also what do you do in a tidally locked planet? Half if not 90 % of it is likely to be unsustainable.

Also a rogue planet without a star might be able to sustain simple life but without human sources of nuclear power the only source of energy would be geothermal, so not exactly exciting candidates for living. Also who wants to live in a planet in perpetual darkness?

Either the “astronomer” author wasn’t a real astronomer at all or this is just clickbait.


"Chris Impey is a University Distinguished Professor of Astronomy at the University of Arizona. He has over 210 refereed publications on observational cosmology, galaxies, and quasars, and his research has been supported by $20 million in NASA and NSF grants. He has won eleven teaching awards and has taught two online classes with over 300,000 enrolled and 4 million minutes of video lectures watched. Chris Impey is a past Vice President of the American Astronomical Society, and he has won its Education Prize. He’s also been an NSF Distinguished Teaching Scholar, Carnegie Council’s Arizona Professor of the Year, and a Howard Hughes Medical Institute Professor. He has written 70 popular articles on cosmology, astrobiology and education, two textbooks, a novel called Shadow World, and eight popular science books: The Living Cosmos, How It Ends, Talking About Life, How It Began, Dreams of Other Worlds, Humble Before the Void, Beyond: The Future of Space Travel, and Einstein’s Monsters: The Life and Times of Black Holes."


Naturally, none of this makes him right... I have no judgement on that point. But does clear some of the ad hominem.


Which is more ad hominem - I only judged the author by what they wrote. Pointing out they’re a professor sounds more like we need to trust them because of who they are.

one could say his career depends on selling this idea that these exoplanets are awesome sauce. Maybe it’s even worse?


I imagine in career depends much more on his peer-reviewed publications and teaching (almost certainly in that order) than on this blog post or one of his presumably many theories.

> Either the “astronomer” author wasn’t a real astronomer at all or this is just clickbait.

Well it turns out he is a real astronomer, and doesn't appear to be a "hack" either as you also said he was.


Sorry for in advance for the dumb question...

Are red dwarf planets over represented due to detection methods?

Or is there some sort of astrophysics related reason red dwarfs would be more likely to have super earth class planets in orbit?

Basically should we hold out hope that with better detection techniques we will be able to detect more planets that are similar to our own.


My understanding is it’s a combination of both - red dwarfs are the most numerous and super earths are the most easiest to detect with them (smaller star, larger the effect of the planet on its characteristics and luminosity).

I am also convinced we will find planets better suited for us than earth eventually. But I doubt any of them would be in any meaningful close distance.

Even if you can imagine a 100 year or 500 year ship (like in Expanse) that can get to a planet 10 LYs away, imagine if it’s 100 or more. We might be SOL.


Better suited in what way? Humans are pretty well adapted to Earth specifically.


> Also who wants to live in a planet in perpetual darkness?

I'd guess in that case people would be living underground in artificially lit environments...

This idea has already been explored by sci-fi. One instance that comes to mind is Wandering Earth where the premise is that people turned the Earth into a planet scale space vessel to escape the sun's expansion and "rehome" the Earth. I'd suggest reading the book rather than watching the movie based on it though.


The sentence:

"If a super-Earth is ejected from its star system and has a dense atmosphere and watery surface, it could sustain life for tens of billions of years, far longer than life on Earth could persist before the sun dies."

is wrong according to the article it references in support. See this comment for details[1].



Yeah, either you orbit at a safe distance, or you get ejected and become a rogue planet.

I'm rather taken with this idea of billions of rogue planets, wandering around the Milky Way, carrying life that's billions of years old. Such a rogue might get captured by a star-system's Oort cloud, gradually drift towards the star, and eventully evince more complicated life. In fact I'm not aware of strong evidence that Earth isn't a rogue (it's about the same age as the Sun, but that's circumstantial, right?)


Also I would expect the amount of cosmic radiation bombarding the surface outside of star's envelope would be significant. We on Earth are extremely lucky that we have molten metallic rotating core (possibly done by collision with another planet/moon very long time ago, not 100% sure here), but that's not the default for planets.

So yes life can be probably only sub-surface one, but that's generally a tough proposition living off what... geothermal vents and volcanic activity? That's hardly a recipe for anything advanced, regardless of time given to evolve.


Well… Suitable for life is not synonymous with convenient for humans. For one, a super Earth makes space exploration much harder - Earth itself is very hard to leave with chemical rockets alone.


If you're calling out the claim in the article, I'd just provide some counter-evidence.

But no, they specifically said most of them are not orbiting red dwarfs:

> Most super-Earths orbit cool dwarf stars, which are lower in mass and live much longer than the sun.


What exactly is a cool dwarf? Doesn’t seem to be a real category - there seems to be one called ultra cool dwarves which is a subtype of red dwarf stars including TRAPPIST-1. Doesn’t exclude the tidal locking problem, but can’t confirm if they are more immune to solar variability and storms.

Also apparently the planets will never be brighter than sunset in earth. The author could have at least mention some of the potential problems. I stand by calling this article disingenuous.


> they specifically said most of them are not orbiting red dwarfs:

The statement, "scientists have found super-Earths orbiting 40 percent of cool dwarfs", specifically links to an article discussing red dwarfs: That article quotes the author of an ESO HARPS planetary survey paper: “[o]ur new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet".

Cool dwarfs seems to be a direct reference to red dwarfs.


Imagine being intelligent life on a super earth 2.5-3x larger than earth but trapped on the planet due to gravitational forces.


Being already semi-intelligent, and trapped here, also due to gravitational forces, I think I can sort of imagine it.


Yea but our civilization can still make it to orbit. It would be very very hard for them to leave the planet.


I don't think Human civilization ever leaves this solar system. The Fermi Paradox isn't a paradox for me, it's about what I'd expect.


Does it mean they can't use ICBM? That's sound like an advantage to avoid self destruction.


Ah, so this is why they haven't visited earth yet.


The rocket equation makes this number fairly calculable.

One doesn't have to go too much larger before it is impractical to get off the planet with even the best theoretical chemical rockets.


Maybe you don't carry your own fuel?

...not saying this is directly applicable, but maybe food for thought?


That's interstellar - which is a different set of problems. The main one is getting out of the gravity well of the planet.

On a super earth, such as Kepler 20b ( ) in order to lift 1 ton of mass to orbit, it would need 9000 tons of fuel -- about 3x larger than the Saturn V. To get the JWST off the planet, it would take 55,000t of fuel. To get that 45t of an Apollo mission off the planet, it would take about 400,000t of fuel over 100x more than the fuel needed for Saturn V.


So conversely the best candidate for a space-faring species might be from a very small planet.


Probably something between Earth and size of Mars. As getting too light makes holding atmosphere harder.


Kind of like how the best candidates for original sea travel came from small islands.


No, because smaller planets cannot hold an O2/CO2/N2 atmosphere like ours.


Imagine how strong they are coMpared to us.

Want to be a gym bro, or do you want to just visit a super earth for a couple years?


Higher gravitation is not only a muscular stress, I believe our internal organs and vessels will suffer or fail relatively quickly because there is not enough growth/strength adaptation designed into them. You’ll be not happy about your digestive tract alone weighing few kilograms more just by default.


A larger planet doesn't necessarily equal higher gravity at the surface.


The gravitational acceleration at the surface is proportional to M/r^2 (where M is the mass and r is radius), and the mass should be proportional to r^3 assuming (big assumption here, but still) the density is constant.

IMO, it is pretty notable that the acceleration at the surface is only linearly proportional the the radius for a constant density, I'd expect something much worse.

Of course we can play with the density but chemistry is, like, way harder than physics.


Sure. An extremely advanced civilization could hollow it out and make a "Dyson planet" -- or just build a shell from scratch -- but it ain't gonna form through natural processes.

I suppose somewhere in the universe there could be a dust cloud of pure lithium that eventually coalesces into a planet, but that seems extremely unlikely. (Interesting premise for a SF story though.)


>An extremely advanced civilization could hollow it out and make a "Dyson planet" -- or just build a shell from scratch

Wouldn't this be impossible because of the planet's molten core? Or am I just biased because our planet has a molten core and I'm assuming it's necessary for a life-bearing planet, or at least unavoidable for any planet where its host star hasn't burned out from old age?

Finally, even if you could remove the molten (or solid) core of a planet, wouldn't the shell collapse due to gravity and other forces?

It seems to me that all these planetary engineering ideas really don't make that much sense. If you have such advanced technology that you can do these things, wouldn't it be faster and easier to build an O'neill cylinder and get exactly the environmental conditions you desire?


maybe not necessarily, but anything else is probably not very likely


Why would you be trapped? The fact that you would need to build a nuclear rocket to escape might actually speed up space exploration on such a planet.


This is exciting, but I think I'm most excited about learning to make self-sufficient and self-replicating colonies in space.

If we focus on settling planets, then each planet is its own set of problems.

But if we focus on learning to live in space, then although it may be harder initially, it's a single problem to solve. Then we just keep working and improving on that solution. And there's a lot more space out there than there are habitable planets. And there's a lot more matter and energy out there than are available on those planets.


I don't really understand the idea of colonizing a planet.

If it is going to be totally independent of Earth, you'll have to set up the entire industrial base and population of that planet.

If it is going to be economically linked to Earth, then we're going to have to deal with shipping stuff there. And, like, what will they sell to Earth? I guess it would have to be really valuable and specific to that planet, to justify manufacturing it there and then lifting it out of a massive gravity well.

Space colonies at least have the hypothetical benefit of zero-g industry, aren't downwell, and can move around. Space colonies in the asteroid belt are the way to go, IMO.


Too many people believe you can colonise planets with the modern equivalent of a horse and covered wagon.

You can't. It's much, much harder than that.

Getting to any kind of self-sufficiency anywhere is going to be incredibly difficult. You literally have to invent a complete industrial production chain for materials, machinery, and food and air that operates in a completely different and much more hostile physical environment with a completely different mix of available raw materials, much less solar energy, and no initial biosphere.


You added a bunch of constraints there which equate it to colonizing an uninhabitable planet like Mars.


Always thinking of the making all the stuff. And I mean literally all the stuff, everything needed during life. In probably more hostile environment than we live. Probably would get old rather fast...


>then each planet is its own set of problems

yes, but we already know how to solve these problems. living in an atmosphere on terra firma with resources is something we can do.

>although it may be harder initially, it's a single problem to solve

hmm, and as of now these are unobtainable solutions: unlimited power source, radiation shielding, etc. so unless one of these planets has a more advanced race that can share how to get over these little hurdles, this plan is just sci-fi


Interesting idea.

To me, exoplanet surveys are one of the most exciting forms of science. I can think of no other thing that would bring us closer to understanding whether or not life does exist in our universe beyond us.

I've long held that it does, but it feels to me that belief is practically religious, completely unfounded. Combined with the fact that I think no other event will impact our world for the better more than knowing this universe has other life... I have my fingers crossed for the giant ground-based teles they listed at the end. Godspeed


> one of the most exciting forms of science.

Not to me, I'm afraid. Suppose we detect CO2, methane and ammonia in the atmosphere of some exoplanet tens of lightyears away. Hell, suppose we detect definite evidence of life. What difference is that going to make to anything? We couldn't launch a probe that could get there in a lifetime, going at half the speed of light. We certainly couldn't get the probe back again. You'd need a generation ship to get people there.

I'm quite sure there's life out there. I'm also fairly sure that very little of the life out there is organised for (or interested in) interstellar travel; and for most destinations, that life would have evolved by the time of arrival, and the space-traveller would be something that can only live in space. A civilisation that can build a rocket has existed on Earth for only a few decades, and might only last a few decades longer.

We could certainly send a probe to Proxima Centauri. Our great-grandchildren could record the results, if they'd spent two lifetimes keeping the probe in contact and under control (fairly boring astronomy career: maintain contact with a spaceship that was launched before you were born, and won't arrive before your grandchildren have died).


I'm gonna get downvoted to hell, but watch the doc, The Phenomenon. It's pretty damn convincing.

As you said, yeah it's a leap of faith without (at least publicly available) empirical evidence, but who cares. It's fun thinking about the possibilities of others out there, interacting, and sharing with them. Even better if they share their tech so we can travel distances off and away from this crumbling rock.

In any case, I believe we've already been contacted, at least since nuke testing, and that the US andnother govs have recovered craft that are handled by contractors. Watch the doc. It's not woo woo crap. I mean Harry Reid is in it and he implies a lot to say thr least.

Here's a link, just use uBlock to get rid of the ads


I’m familiar with the so-called evidence you’re discussing. The thing is, there’s no reputable, authoritative source that will go on record right now saying we are positively being visited by aliens. Nobody seems to know exactly what the phenomenon is, if it really does exist. More to the point, the notion of aliens themselves could very well be a culture-bound idea, just like angels and demons and fairies and spirits. We just don’t know. It could very well turn out to be propaganda and disinformation that hides something else entirely.


It's interesting that planets could roam between solar systems for 10's of billions of years before becoming uninhabitable, and that such planets are likely common.


This would be such an amazing premise for a scifi movie. One such planet drifts through the solar system, and we have like 3-5 years to make contact with whatever lives there before it drifts away.


There kind of is already:

The premise is that humans turned the Earth into a planet-scale space vessel to escape the sun's expansion and rehome into a different solar system. Basically involved de-orbiting the Earth and coming up with a way to fling it out of the solar system whatnot.

The sci-fi parts are quite interesting, though I'd recommend the book instead of the movie (which is really a mediocre Chinese take on the Hollywood blockbuster...)


> which is really a mediocre Chinese take on the Hollywood blockbuster.

I quite enjoyed the film. It was interesting to see a different cultural take on how to solve "future problems" in a different cultural SciFi. Would I watch it again? Probably not, was it any worse than the stream of MCU junk? Not really.


Shorter time scale but - Rendezvous with Rama by Arthur C Clarke


There was extraterrestrial life in that one, or am I thinking of hammer of god?


They can't. That sentence in the article is wrong according to the paper it references to support the statement. See [1].



> By definition, super-Earths have many of the attributes of a super habitable planet.

Is that true?

> A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively.[1] The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability.


That's mentioned in the article:

> A super-Earth is any rocky planet that is bigger than Earth and smaller than Neptune.

If you read further in the article, it explains why super-Earths are a good target to look at for extraterrestrial life.


But the “by definition” part seems incorrect. Nothing in the definition of “Super Earth” indicates superior habitability.


It may not be worded well but it does state why. Planets of this size are more likely to be geologically active, a sufficient size to retain an atmosphere thick enough for life, a strong enough magnetic field, etc.,. Just due to their size, they are better suited to support life then (at least as we know the conditions necessary). I mean between the other options - planets so small they're basically rocks in space and giant gas planets with a bunch of other issues - it seems this classification of planets indeed offer superior habitability.


The author goes on to explain why super earths are a good place to look for habitable planets. It’s the entire point of the article. Planets meeting this definition also tend to have other characteristics as well.


Super Earths are easy to find and super common but I am almost betting the most life will be found in gas giant moons. Even though we don’t have any gas giants in our own system that have Earth-sized rocky moons, each one of ours has half a dozen “almost-there” moons. A civilisation developing around a gas giant with multiple habitable and easily accessible moons would be very interesting.


Magnetosphere of planet like Jupiter or Saturn is the most radioactive place in solar system... Also energies (delta V) needed to travel between Jupiter moons are greater, than those needed for travel between solar planets.


> Magnetosphere of planet like Jupiter or Saturn

I thought Saturn was mostly benign. My hope was that a magnetosphere would protect the moons from the early outbursts of the red dwarf.

> Also energies (delta V) needed to travel between Jupiter moons

That's surprising. Found this nice map [1] and the numbers are really disappointing. ~15 kps from Titan-to-Iapetus sucks (even though it's ~4 kps less than Earth-to-Mars). At least the distances are smaller...


> While there are many reasons why a habitable world would not have signs of life, if, over the coming years, astronomers look at these super habitable super-Earths and find nothing, humanity may be forced to conclude that the universe is a lonely place.

Interesting... The "no" is definitely cheaper and faster than the "maybe" or "yes." If we get a "no", what's next? Planet-wide depression?


Yes means there is life out there. No means there isn't life in the specific place we looked, but the universe is very big. So no is really pretty meaningless.


No has to be understood to be “maybe.” if there’s one negative that will be very very hard to ever approve, this is it.


> So the most habitable planet would have roughly twice the mass of Earth and be between 20 to 30 percent larger by volume.

So, ~60% denser than Earth? Density is mass/volume, and 2x / 1.25x = 1.6x.

The math works out really well if they meant a 20-30% larger radius: 1.25*3 = 1.95, so similar density but larger volume.


Wouldn't it be physically impossible to escape the gravity of a super Earth using the currently available and known propulsion technology we have here on Earth?


Not quite, but as mass increases relative to Earth, launch vehicles become increasingly ridiculous. Many "super-Earth"s would need something like a Saturn V to get to their equivalent of the ISS, or maybe even their equivalent of Sputnik, depending on exactly how "super".

When you start to get into gas giant mass, chemical launch starts to become really close to impossible instead of just wildly unaffordable.


We haven’t even come up with a material strong enough to build a space elevator here on earth. On a heavy planet you need an even higher strength to weight ratio.

Your space platform would practically have to be a floating city, since mountains won’t even be as high.


If they're bigger then they have more mass and therefore a higher gravitational pull, which makes every task more expensive.


We don't have to live there. If there is a sentient industrial space faring equivalent of our species then trade, cultural exchanges etc can be performed off-planet. There are ways around these problems.


Natural selection would just favour smaller body sizes. Ants can lift tens of times their own weight. The question is, what's the minimum body mass that would still allow human-like intelligence?


Depends on the density, and the distance from the surface to the centre.