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Summer on Neptune
Martian-mooncat writes "According to New Scientist Neptune is now entering a 40-year summer. The report says that cloud cover changes show Neptune has its own seasons, despite being 4.5 billion miles from the Sun. There are some pretty Hubble pics too!"
From the article:
;)
"These extreme conditions on the surface of the gas giant are believed to be largely driven by heat from Neptune's inner core of molten rock, liquid ammonia and methane."
There ya go.
IIRC, Jupiter radiates more total EM energy than it gets from the Sun, but most of that is in radio and IR, not visible light. Dunno about the other gas giants. Neptune, surely. Saturn and Uranus, maybe not; they're enough closer to the Sun than Neptune, and enough smaller than Jupiter, that they might break even. Just guessing, of course. It's been a long time since I read up on this stuff.
The correlation between ignorance of statistics and using "correlation is not causation" as an argument is close to 1.
Jupiter does indeed emit about twice as much energy asn it absorbs (not reflects) from the Sun. This indicates an internal heat source. "Core temperature" isn't a very accurate description, based on what we think is going on, though. Jupiter isn't a failed star, especially in the standard planet formation scenario where it forms an icy core before accreting gases. So don't look to fusion to create the heat, the planet's structure is likely (we're not absolutely certain that there is a core) wrong for that. What powers Jupiter is probably slow, continued contraction. As the planet shrinks, it loses gravitational energy and emits that as heat.
Saturn has the same input/output disconnect. In the case of Saturn, I believe that the current model is helium rain. (Also releasing gravitational energy.) And Neptune also emits more energy than it takes in. (Oddly, Uranus doesn't.) Neptune's heat source is somewhat more ambiguous, but helium rain could be it. However, we know that Uranus and Neptune have very large icy cores (well, large proportional to their overall size), so there is definately no fusion there. It's doubtful that the core could be responsible for the extra heat, since there aren't many ways for ices to generate heat.
Jupiter isn't really a failed star... a failed star is a "brown dwarf", jupiter is merely a gas giant. Where exactly brown dwarfs lie is kind of hard to know exactly (astronomers still debate this)... but somewhere around 15x jupiter mass you would have a brown dwarf, and if you keep going beyond that you will soon reach the minimum size required for a star.
D.
You can tell how powerful someone is by the magnitude of the crime they can commit and be able to get away with.
No, the extra-solar planets were a bit of a shock and a sticking point for a bit. But I think most planetary scientists are confident that the giant planets simply migrated inward as part of the formation process. (There were proposals for this years before the first exoplanet was discovered.) The details are still unclear, but I think there's a reasonable consensus that the model still works.
And you're exactly right about the detection method (Doppler shifts in the stars): it's biases towards massive planets with eccentric orbits and small semi-major axes. What we've found isn't likely to be a representative sample.
Jupiter could never have been that large. It would have had to enveloped all of the inner moons, including the 4 Galilean ones.
I've done the integration and calculation for a homogenous Jupiter (constant density), and the planet would have to have been 25% larger 4.5 billion years ago to have produced the current energy excess that we see today for its entire life. This isn't terribly unreasonable, especially since the transiting extra-solar planets that we've seen have somewhat larger radii than Jupiter does. (The planets can't expand when they get closer to their stars, but they are prevented from contracting as far as Jupiter, say the modellers.)
In fairness, I should note that there are those who think Jupiter's energy excess is due to it's energy of accretion which hasn't leaked out over the past 4.5 billion years. I usually hear the contracting explanation, though.