In my amateur opinion, red dwarf stars have one advantage over stars like the Sun, and that is time. Our own Sun may not be able to support life on Earth for much more than another billion years, and Mars too will become too hot in four billion years or so. And in yet another one or two billion years, the Sun will become a white dwarf, and be useless as a life-nurturing source of energy for the solar system.
But red dwarfs have all the time in the world. If they don't get their life-nurturing properties right the first time, or the second time, or the thousandth time, they can try again and again. Their own lives have just barely started. To put it differently, red dwarf stars can play the "life lottery" again and again and again for probably trillions of years.
Yes, but does that mean that red dwarfs are better, or just as good as, the Sun as a star that can uphold life on at least one of their planets now? Not in my opinion. Their habitable zones are incredibly close in - much closer than Mercury's orbit around the Sun! - so that the planets are not only going to have bound rotations (or possibly almost bound, like Mercury's) - but the planets will also be extremely vulnerable to any unforeseen outbursts on their suns. It's beyond me how people can be so hopeful of the chances of finding life now on any of the three worlds of TRAPPIST-1.
So the only reason for the enthusiasm that I can understand is that the TRAPPIST-1 planets are close enough to the Earth, and their star is sufficiently faint, that Earthly instruments can take a good look at the planets and really look for signs of life. If any of the planets have life that interacts with and alters the planet's atmosphere, Earthly instruments should be able to detect that.
But I'm reminded of the old story of the man who had lost his keys, and who looked for his keys under the streetlight. Another person asked him if he had lost his keys under the streetlight. No, the man replied, I lost them over there, but it's too dark to see them over there.
Last edited by Ann on Sat May 07, 2016 5:04 pm, edited 2 times in total.