Simon_Jester wrote:In fact, gravitational contraction was widely accepted in the 19th century as the source of power that allowed the Sun to keep shining, since it was the only thing then known that was even vaguely adequate to the task.
Ah, so you've never heard of the bright spark (name forgotten) who laboriously calculated how long the sun would keep on burning until it ran out of coal...?
I am, but the conclusion of that was that, well, it wouldn't run long enough to be even vaguely plausible.
At least, after things got widespread and were analyzed by many, as I recall.
loomer wrote:The consensus actually diminished recently thanks to Kepler 10c. ~2.3 earth radii, ~17 earth masses, higher density than earth has and thus necessarily not a mini-neptune, but the first discovered mega-earth.
That's true, although Kepler-10c orbits very close to an old star (10.6 billion years old), and an estimated 5-20% of its mass is in volatiles/"ices" form. That means it likely has a "mantle" that's small compared to the overall size of the planet, but much thicker than Earth's atmosphere. In fact, the whole thing might be a leftover rocky core from a gas giant that's had its atmosphere blown off over time.
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