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Also, about prospects for life, do you put the Trappist-1 system near the top? But since it's a red dwarf, what sunlike stars would you say have planets that are near the top of the list?
From my academic standpoint (biology)? I would not put it at the top ten most likely to host life
(even though it is unfeasible to concoct such a list due to our lack of knowledge) - maybe if I was pressed I'd put it at the top twenty. My reason for this is that we simply know too little about the system to jump to such hasty conclusions about life exiting there in any form and it's human habitability.
We should think about our First Principles - What we know:
The TRAPPIST-1 system is comprised of super-earths, close to a star which is a low-mass but highly active red dwarf. When studied over a period of 80 days by Kepler, seven powerful flares from TRAPPIST-1 were detected. Since the star's planets orbit quite close to it, these storms could cause an estimated 10–10000 times more damage then even the strongest to assail the Earth. Not only will this radiation directly damage anything on those planets, but they can also alter the chemical composition of the planetary atmosphere and temperature in the long term. Compared to such storms, the TRAPPIST-1 exoworlds would need magnetic fields of about 10–1000 Gauss
to be shielded from such flares. What we don't know:
The exact geophysical characteristics of super-earths in regards to atmospheric, geological and magnetic planetary formations and how these processes can alter under extreme conditions like close proximity to a star. This is an interrelated study to the exact behaviors of tidally-locked exoworlds as well. Also, while current studies hint at a mostly-hydrogen-free atmospheric environment for all the TRAPPISt-1 exoplanets, this ultimately proves nothing aside from determining their maximum mass. So we don't know what their atmospheric content is until the James Webb space-telescope comes along. All in all, based on what we know so far, it would be naive to conclude that the TRAPPIST-1 system is an abode to life unless the solar-systems environment during abiogenesis was very different (i.e the star was less active and a suitable planet developed a strong magnetosphere. This is unlikely since young red dwarf's are usually quite active).
Nonetheless I still consider it possible that red dwarf-systems can host life, and TRAPPIST-1 might
be one of those, perhaps sporting some sort of deep-crust/geothermal or ice-shell biome.
As for what other solar-systems I consider more likely to have ET life living in them, none come to mind. Until we can exhaustively study the properties of each exoplanet, our current database is inadequate. To many unknowns present themselves to make any scientific conclusions. Theories abound though. This isn't disproving ET life exists, it's just a dose of humility to illustrate that we ultimately haven't been looking for long enough nor using the right techniques (atmospheric spectroscopy is a good start in this regard).
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And I saw floaters being mentioned as possible signs of life above gas giants, can the same be said for life existing in the atmospheres of cool brown dwarfs?
Yes, if the right conditions are met. A more placid atmosphere would be required, along with a ready source of some sort of medium for abiogenesis, like H2
O. Life wouldn't be able to exist deep in the crushing depths of a jovian exoplanet, nor too far up in the clouds where radiation is rampant (bear in mind that brown dwarfs tend to have stronger radiation fields then jovians in solar-systems). The exact altitude depends on the life in question and their hosts atmospheric conditions. This is a very rough generalization.