Thread: Huge Earth-ish planet?

Huge: Can there be a (relatively) earth like planet that's 3 times as massive? (or would such a large planet most likely accumulate atmosphere and become a small gas giant) ?


Gargantuan: If there was a planet like earth (same proportion of iron, etc) that was twice as large as the sun, would it collapse into a black hole?

It all depends on density. A planet might be huge in proportions, but the surface gravity might still be close to that of earth due to the inverse square nature of gravity.

When you say twice as large, what do you mean exactly? Twice the radius, with the average density of the earth?

Originally Posted by icewendigo

Huge: Can there be a (relatively) earth like planet that's 3 times as massive? (or would such a large planet most likely accumulate atmosphere and become a small gas giant) ?

Not just the planet's size but its average and high temperatures are important, as well as its proximity to its star. For Earth-like temperatures, such a planet would very likely have a much bigger atmosphere. For hotter temperatures the atmosphere would tend to be less, and for colder temperatures a larger atmosphere. Such a water planet like Earth might be able to support Earth-like sea life, and maybe some similar plant life, but Earth type animals would probably be crushed by such an atmosphere, probably greater than the crushing atmosphere of Venus.

Gargantuan: If there was a planet like earth (same proportion of iron, etc) that was twice as large as the sun, would it collapse into a black hole?

Hypothetical: For a mass somehow starting at a temperature of the Earth, but twice the mass of the sun, what could it become? Stars can exist at 100 times the mass of the sun. I would expect this mass of your hypothetical planet to eventually become a star. According to theory, it takes an explosion and core implosion to create a stellar black-hole. An exploding star (supernova) with a remaining mass greater than about 1.4 solar masses can accordingly create a neutron star or black hole instead of a white dwarf star. Your star seemingly would not be big enough to go supernova with Earth-like internal elements, after becoming a single star system.

Originally Posted by KALSTER

It all depends on density. A planet might be huge in proportions, but the surface gravity might still be close to that of earth due to the inverse square nature of gravity.

When you say twice as large, what do you mean exactly? Twice the radius, with the average density of the earth?

I don't think it does, the core of a planet is mostly made out of ferromagnetic elements like iron or nickel, and those are pretty similar in density. What you try to say is, if a planet's core is made out of lighter elements such as carbon, although its size would be huge, the gravity would be low. There's 2 problems with that. The first problem is that, if a planetary core is not magnetic, it does not generate a magnetosphere around the planet, meaning that the planet cannot sustain life. Second, the probability for the carbon/iron ratio to be so huge in order to create such a planet is very low. Combined with the low probability of being at the right radius from the sun, and finding life etc. etc. I'm not saying it doesn't exist, I'm saying we won't come across it, ever.