/ Rogue planet, 400C - how can this be
the report says "The team believe it has a temperature of about 400C and a mass between four and seven times that of Jupiter "
how come its so warm if it hasnt got a star? its pretty big, but the surface temperature of jupiter is still -145 degrees C. So do they mean core temperature or something? Or is it just a typo or the reporter misunderstanding? Any of the astronomer types on here know?
Here are some of my thoughts
1) Gravitational heating, caused by increased pressure as the planet contracts from when it WAS orbiting a star. This effect significantly warms jupiter. If it were larger then the gravitational compression would be enough to cause it to undergo nuclear fusion in the core and turn into a star.
2) Radioactive decay, this would be a fairly small effect.
3) Tidal heating caused by an as yet unseen body orbiting it.
1. Its a death star, time to leave the planet.
Hats off to the person who got the themometer on there!
It's a young planet. That means it is still coalescing out of the stuff it was made out of, and that means it is contracting. As it contracts it releases gravitational potential energy, and that energy gets converted to heat. Indeed, this is how they managed to estimate the age of the planet as 50-120 million years old. This process would be over after a couple of hundred million years old. Jupiter is much cooler because it is much older (4.5 billion years).
what's it doing out there then...? taken a bit of a shunt in an evolving solar system?
and is that quite big for a planet? i thought jupiter was pretty big already. how big can a planet get before it becomes a brown dwarf star...?
ps where you been, thought you'd have some comment to make on the eclipse thread....?
Most likely yes, some multi-body near collision with something heavier that sling-shotted it out of its solar system. (Or, much less likely, it formed in situ in a region without enough stuff to form anything heavier.)
> get before it becomes a brown dwarf star...?
They're claiming that one as 4 to 7 Jupiter masses, which is fairly common; planet masses peter out at about 20 Jupiter masses. Brown dwarfs are then heavier than about 30 Jupiter masses. You need about 75 M_Jup to burn hydrogen and so be a star. (You can burn lithium at > 13 M_Jup, but nowadays that isn't considered sufficient qualification to be a brown dwarf.)
is it easier to fuse lithium than hydrogen? i thought that it became progressively harder to generate fusion with higher atomic masses...?
Sorry, I meant deuterium, not lithium. Deuterium is easier to burn than hydrogen (no involvement of weak-force needed).
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