What is the maximum mass a rocky planet (like Earth) can have?
And what happens if more mass is added to this theoretical maximum mass? Does the rock change into gas?
That seems an odd thought. So, I might wonder, could a rocket planet exist with the mass of Jupiter?
- Jeffrey KLv 72 years ago
About 10 to 15 times earth's mass is the maximum. If a planet has more mass when its solar system is forming, its strong gravity will attract and hold on to lots of hydrogen and helium and other gasses. This is make a huge dense atmosphere. It will become a gas giant like Jupiter. The core of all gas giants probably is a ball of rock about 15 times earth's mass.
- cosmoLv 72 years ago
Your question is: what happens if you keep adding rock and iron to a rocky planet?
It does matter a bit how you add the material. If you drop it on the planet from a great height, the energy deposited when it hits will liquefy the planet, making it a ball of lava. If you deposit the added material gently, it can accumulated as a rocky mass until the pressure in the center begins to free the electrons from the atoms. In any case, as more and more material is added, the core of the planet will begin to be supported by electron degeneracy pressure due to free electrons, like the material in a white dwarf. Such material can persist at a wide range of temperatures at approximately constant density, as long as the pressure is high enough. Adding enough material will essentially convert the entire planet into a white dwarf star. (Or a "black dwarf" if you keep it cool enough.) The density will be way up and the radius of the planet will decrease. Eventually, it will collapse to a neutron star (causing a supernova-like explosion). Keep adding material and you'll eventually get a black hole.
So where along this process does it stop being a "planet" and start being an "ultra-high metallicity star"? Probably somewhere around 1/10 of a solar mass. Time is an issue as well, because the radioactivity associated with rocky material will tend to keep the whole thing molten for billions of years. It's hard to get that much material together without depositing energy in some form, and once the planet is large it will have a hard time cooling enough to solidify the surface.
- 2 years ago
Thy're called Super-Earths. May 2014, previously discovered Kepler-10c was determined to have the mass comparable to Neptune (17 Earth masses). 014With the radius of 2.35, it is currently the largest known planet likely to have a predominantly rocky composition.
What you're suggesting is physically possible, at that extreme gravity may prevent a gaseous rocky atmosphere (iron gas?) but beyond a certain mass a rock planet would be a large liquid rock planet.
- 2 years ago
The smallest known star is 83 times the mass of Jupiter. The largest known planet is likely less than 10 times Jupiter's mass. The sun is about 1000 times more massive than Jupiter.