Well, it appears I was wrong when I said that Beta Pictoris b was the first directly imaged planet orbiting another star. That honor apparently goes to Fomalhaut b:
All right, but Fomalhaut is another blue star of spectral class A! So the first
two directly imaged planets orbiting other stars are in orbit around two different class A stars, which are both about twice as massive as the Sun! What a coincidence!
Speaking about the importance of a star's spectral class and its likelihood to have planets, it is my impression, as I have said, that astronomers are very interested in low-mass stars, even stars which are a lot more lightweight than the Sun. Of course the real reason for this is almost certainly that astronomers are really looking for potentially life-bearing planets, and then conventional wisdom has it that planets orbiting high-mass stars won't do.
So what do the experts say? Why do we live on a planet orbiting a G2V star? Stars of spectral class G most certainly aren't
rare in our galaxy, but they definitely arent
typical, either. Compared with small cool stars of spectral class M, stars like our Sun are few indeed. In view of the fact that stars of class M are so
very much more common than stars of class G like our Sun, isn't it strange that we orbit a star that is so, well, untypical?
The way I see it, there are two possible reasons why our living planet orbits a star of spectral class G. One possibility would be that life might be so commmon in our galaxy that most stars can be expected to have at least one life-bearing planet, and in that case it is sheer coincidence that our star is of untypical spectral class G. It also follows from that line of reasoning that if we manage to travel to a star of class M, we can expect to find a life-bearing planet in orbit around it.
The other possibility would be that life, at least complex life, is very very uncommon, and it only comes into existence where conditions are just right. If so, it is probably no coincidence that our Sun is of spectral class G, and it also follows from that reasoning that if we travel to a star of spectral class M, we probably won't find life on any of its potential planets.
A third possibility is that "the life-friendliness of the spectral class of a star" is a function of the age of the universe. Perhaps life is far more probable on a planet orbiting a class G star
now than on a planet orbiting a class M star, now that the universe is about 14 billion years old. It could be that when the universe is twice as old, or five times as old, most G stars like our Sun will have burnt out and any life on their planets will have expired. The M dwarfs will remain essentially the same, however, and life will have time to keep trying to come into existence on planets orbiting these tiny stars. The likelihood of life existing on planets orbiting stars of class M may increase over time, while it will almost certainly decline over time for stars of class G.
Well, these things are certainly interesting, in any case!
Ann
A Giant Planet for Beta Pic
