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!"

Comments

Selling tickets

[KDan]

Selling tickets for a 40-year holiday with guaranteed permanent sun-tan!!!

Daniel

Cold one, eh?

[Sherloqq]

Hmm... Summer on a planet 4.5 billion miles from the Sun... ... The planet's average surface temperature is thought to be about -218 C ... Wow... almost as bad as Canadian summers :)

Where's it coming from?

[zeugma-amp]

From the article:Observations indicate that Neptune experiences some very extreme of weather conditions. The planet's average surface temperature is thought to be about -218 C, with storm winds of up to 1500 kilometres per hour.

One would think that so far from the sun, the energy recieved by Neptune would be fairly feeble. What is driving winds like that? I would have to guess it is core temperature. I've often heard of Jupiter referred to as a 'failed star'. I'm not exactly sure how accurate that is, but from what I've read about our guesses of the planet's internal dynamics, it's a moderately accurate portrayal. (I believe it even emits more light than it reflects from Sol. I've never heard the description applied to Uranus or Neptune, but I wonder if it would accurately be said of all the gas giants. Comments anyone?

I also think that it's interesting to consider that given the really long orbital periods of the outer 3 planets, we've not really been able to observe much of the changing conditions (i.e. seasons) one would normally associate with the variations that occur over the period of a complete orbit.

Re:Where's it coming from?

[Daniel Dvorkin]

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.

Re:Where's it coming from?

[CheshireCatCO]

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.

Re:Where's it coming from?

[DiSKiLLeR]

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.

Re:Where's it coming from?

[CheshireCatCO]

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.

Re:Where's it coming from?

[CheshireCatCO]

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.

Summer on Neptune has got nothing over�

[Anonymous Coward]

...fall on Uranus.

That's something to write home about!

Only in the south

[meiocyte]

>Researchers from Wisconsin-Madison University and NASA's Jet Propulsion Laboratory found that Neptune's southern cloud bands have been getting steadily wider and brighter over the past six years.

I take this to mean that it's only beginning summer in the southern hemisphere. Make sure to take this into account when you're selecting your vacation package.

Hmm. Slow news day, I guess.

Summer indeed.

[DoraLives]

Neptune is now entering a 40-year summer

And may I ask what, pray tell, has been going on in the other hemisphere for the last forty years?