3 new planets could host life

[longship]

63. Let me put it this way.

Every single smaller planet in the universe which we've studied has high density. What I mean by smaller is smaller than the medium sized Ice Giants like Uranus and Neptune. This means millions of objects in our solar system alone. All four of the inner planets, all the moons, all the ice dwarfs, and all the uncountable myriads of asteroids. All are rocky, composed of high density compounds. Of all the extrasolar planets discovered that we have data on, none violate this trend.

Not a single one is styrofoam density or even close to such. The only planets of low density are large gas giants. There is a reason for that. It is in the equations for gravity -- Newton would suffice. It can be modeled on a computer.

I have not done the modeling, but I highly suspect that there are no low density small planet-sized bodies among the multitude in our solar system alone because such a thing would not be stable; its self gravity could not hold it together.

Take Phobos, for instance. It has a relatively low density. But it's what is called a rubble pile, a collection of dense rocks held together by their mutual gravity. That's probably close to the limit. Also, it's a very small object, which may help. It's that problematic R-squared term in the denominator. Gravity diminishes as the square of the radius. So you either have to have a large mass which increases density for small objects. Or, to have low density, you have to have both a huge radius and large mass. Which is what I've tried to describe to you in these posts.

There probably isn't a way to have both low density and an earth-sized planet at the same time. We certainly don't see it in the thousands of objects we've studied. Very small things (check out Phobos) and very large things (Saturn) don't have to obey those rules. Phobos because it's small; Saturn because it's very massive. There may be a continuum between, but I would bet my bottom dollar that there is a null between them where there is no stable solution.

Interesting discussion, just the same.