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TRAPPIST-1's exoplanets appear to have migrated closer to TRAPPIST-1 over time until they reached their current orbits. This migration appears to have allowed them to retain too much water to support life:
What [the ASU-Vanderbilt team] found through their analyses was that the relatively "dry" inner planets ("b" and "c") were consistent with having less than 15 percent water by mass (for comparison, Earth is 0.02 percent water by mass). The outer planets ("f" and "g") were consistent with having more than 50 percent water by mass. This equates to the water of hundreds of Earth-oceans. The masses of the TRAPPIST-1 planets continue to be refined, so these proportions must be considered estimates for now, but the general trends seem clear.
"What we are seeing for the first time are Earth-sized planets that have a lot of water or ice on them," said Steven Desch, ASU astrophysicist and contributing author.
But the researchers also found that the ice-rich TRAPPIST-1 planets are much closer to their host star than the ice line. The "ice line" in any solar system, including TRAPPIST-1's, is the distance from the star beyond which water exists as ice and can be accreted into a planet; inside the ice line water exists as vapor and will not be accreted. Through their analyses, the team determined that the TRAPPIST-1 planets must have formed much farther from their star, beyond the ice line, and migrated in to their current orbits close to the host star.
[...] "We typically think having liquid water on a planet as a way to start life, since life, as we know it on Earth, is composed mostly of water and requires it to live," Hinkel explained. "However, a planet that is a water world, or one that doesn't have any surface above the water, does not have the important geochemical or elemental cycles that are absolutely necessary for life."
Also at Phys.org.
Inward migration of the TRAPPIST-1 planets as inferred from their water-rich compositions (DOI: 10.1038/s41550-018-0411-6) (DX) (arXiv)
Related: Powerful Solar Flares Found at TRAPPIST-1 Could Dim Chances for Life
TRAPPIST-1 Older than Our Solar System
Hubble Observations Suggest TRAPPIST-1 Exoplanets Could Have Water
Induction Heating Could Cause TRAPPIST-1 Exoplanets to Melt
Another TRAPPIST-1 Habitability Study
(Score: 0) by Anonymous Coward on Thursday March 22 2018, @03:09AM (11 children)
Why should land surfaces even be required? We still don't have 100% proof of how and where life started on Earth. It may take a few billion years longer without land surfaces (e.g. just the right sequence of cosmic rays to zap stuff near a hydrothermal vent) but so what?
And that's just for life as we know it.
(Score: 5, Insightful) by takyon on Thursday March 22 2018, @04:10AM (10 children)
There's a little more to the story than "Wow, it's covered with water":
https://www.sciencemag.org/news/2015/08/why-water-worlds-won-t-host-life [sciencemag.org]
And from the arXiv for this paper:
https://arxiv.org/abs/1706.02689 [arxiv.org]
There could also be a pressure problem if these planets have oceans that are hundreds of times more massive than Earth's, along with higher gravity in some cases.
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(Score: 2) by captain normal on Thursday March 22 2018, @05:16AM (9 children)
Here on Earth we have many forms of life that live and go down into depths like the Marinas Trench where pressures are huge compared to the surface pressures. High pressure is a bogus argument.
When life isn't going right, go left.
(Score: 3, Insightful) by takyon on Thursday March 22 2018, @05:19AM (6 children)
And if the pressure was 100 times greater than in the Mariana Trench?
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(Score: 2) by Bot on Thursday March 22 2018, @06:34AM (3 children)
it does not matter really. life is about behavior not chemical composition, the good old grow multiply populate, it may happen at vastly different time scales/conditions. It is not even a theological problem as somebody liked to reduce it to. Adam and Eve are the pinnacle of creation as physical entities able to recognize their creator or something like it. Not necessarily because they are the first or the only ones.
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(Score: 2) by Reziac on Friday March 23 2018, @03:11AM (2 children)
By that definition, the Yellowstone Hot Spot is alive.
And there is no Alkibiades to come back and save us from ourselves.
(Score: 3, Touché) by Bot on Saturday March 24 2018, @02:39PM (1 child)
Does it populate, that is morphologically adapt to different conditions and spread? Then it is alive.
Don't be a carbon-based-life-form-ist.
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(Score: 2) by Reziac on Saturday March 24 2018, @03:32PM
LOL! modded up. :D
And there is no Alkibiades to come back and save us from ourselves.
(Score: 0) by Anonymous Coward on Thursday March 22 2018, @08:16AM
You are getting very close to an old creationist argument: Earth is so perfect for life that it must have been created by an intelligent designer to have exactly the properties that life needs. No. This life evolved on Earth, and thus the properties of Earth are the properties that life evolved to live in.
Life on a planet where the oceans have 100 times greater pressure will evolve to live in oceans with 100 times greater pressure.
(Score: 4, Interesting) by Immerman on Thursday March 22 2018, @01:15PM
Waterborn life is, generally speaking, neutrally buoyant - life evolved for a particular depth range generally remains there without trouble. Sure, it may occasionally get caught in a down-current and crushed by the pressure, but so long as that doesn't happen to the entire population, it's not really a problem.
Meanwhile, deep-sea life doesn't suffer any ill effects from the pressure, since its internal pressure matches that of it's environment - in fact being pulled to the surface would be fatal as its cells rupture and/or dissolved gasses come out of solution.
The only reason pressure would be a problem is if it interfered with chemical processes - and given that liquids are relatively incompressible that doesn't really happen - chemical reactivity in a gas increases with pressure (more molecular collisions per second), but it has negligible effect on solids or liquids.
(Score: 4, Informative) by PinkyGigglebrain on Thursday March 22 2018, @04:12PM (1 child)
Not entirly. Deep-sea pressures do affect chemical reaction rates somewhat, speeding up reactions. Organisms adapted to these pressures may experience metabolic problems when brought to the surface for study. [noaa.gov].
BUT, that does not preclude life evolving under the extreme pressures of one of these worlds. As to the whole "..does not have the important geochemical or elemental cycles ..." bit I call BS. Deep sea geothermal vents put plenty of the needed elements for life into the water, I've read several recent theories that say the vents might have been where life started on Earth.
If there is one thing about life that is probably a Universal trait it is that if there is any chance at all it WILL happen.
"Beware those who would deny you Knowledge, For in their hearts they dream themselves your Master."
(Score: 2) by Bot on Saturday March 24 2018, @02:44PM
Indeed life is more stable than the immutable.
Just as freedom with rules is often more free than literal anarchy.
That is, GPL > BSD license.
Done trolling for the day, have a nice weekend.
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