The frost line is the point in any stellar system where it is cool enough for volatiles like water and methane to move from gas to solid. In our solar system this is between Mars and Jupiter.
Ten earth masses is thought to be a special mass in terms of planet formation. It is the mass that allows the gravity of the planet to start to affect the surrounding gasses in a meaningful way. That is, it draws the gasses faster than before and the added gasses increase the mass which increases the amount of gas accumulated, in a never ending cycle until there is no more gas to collect.
Kepler 22b is in a odd position, it is large and it is possibly low mass and it is warm.
The warmer the planetary body is, the faster it's molecules are traveling, and thus the closer they are to the planet's escape velocity. Escape velocity is a function of the mass and the radius of the planet.
There are two possibilities as to where Kepler 22b formed, it formed where it sits or that it formed further out and migrated in to the warmer solar system. Each has it's own set of problems and coolness.
Formed in place, two more possibilities, rocky world and dwarf gas giant:
Rocky world like our own, a core of rock in the neighbourhood of around fifty earth masses of rock with a few earth masses of water. The escape velocity is such that CO2 is held strongly, as is O2 and N2, all H2 and He is swept into the outer star system. Water is held, but had to have arrived via comets same with the other gasses too. This means Kepler 22b is like earth in many ways, slightly lower gravity, slightly warmer and much larger surface area. It has a molten core, that will remain molten much longer than our own will. Depending on its rotation period, it will have a magnetic field surrounding it. Given its distance from the star and the size of the star, Kepler 22b is not locked to the star so it should rotate and have a healthy magnetic field. It probably has plate tectonics and a functioning carbon cycle. It might be a fun place to live, life is most certainly present.
Dwarf gas giant born on site. As a star forms the unused materials form a disk and it is from this disk everything else is formed. The parent star of Kepler 22b is smaller and cooler and took longer to blow away the disk that had formed prior to star ignition. Did the disk cool more before this happened, did the frost line start closer to the star initially? If it did, Kepler 22b could have begun accumulating a lot of mass prior to stellar ignition. It comes back down to a question of mass. If it is a dwarf gas giant, it must be massive, otherwise the gases would escape easily.
Migrating planet. Much like the Dwarf gas giant, just cleaner from what we already know about the frost line and stellar formation. How it moved? Large impacts or nudged by something else in system.
There are other models that might create a planet so large and close, they are nearly improbable, but still possible, like rogue planets entering and being captured by the star, but in a young universe, that is most unlikely.
Okay, looks like as usual, I need to double check all my calculations with reality. I was a wee bit wrong. Okay very wrong. I recalculated it though.
ReplyDeleteKepler 22b is assuming earth like density has 14 times Earth's mass and 2.4 of Earth's radius, meaning a gravity of 25 newtons or 2.5 times our gravity. That said I believe the density is less and there for the gravity would be less, and would contain more water and other volatiles, if it had half our density it would have half the above gravity. It would be a water world I have little doubt as all the terrestrial planetoids do not equal 14 earth masses, but if one includes the gas giant cores there would be more than enough. Still we would need to observe this star for fifty years to determine if there are gas giants in the system.
It looks like a wonderful world to travel to, it is a good thing that we can't yet.