Established Member
Recent observations show that the temperature recorded at the poles of certain planets and moons in the solar system is higher than would be expected or predicted by direct thermal heating from the sun. Does anyone know if and how current theory can account for this?
Order of Kilopi
You'd need to give us some examples if you want specifics.
But there are certainly other sources of heat apart from direct insolation: atmospheric circulation, radioactives and tides spring to mind.
Grant Hutchison
Banned
Bold Mine:
The way you worded this implies that 'current theory' is somehow faulty that it overlooked this.Originally Posted by ATKINS
No- maybe there is another factor as to why they are a bit warmer.
I don't know what that factor might be off the top of my head without any examples from you. I just wanted to comment on that wording.
Established Member
The first system that springs to mind is the Saturn system, with recent findings concerning the hot north and south poles of Saturn itself and the hot south pole of Enceladus. The temperature data is provided by Cassini.
Order of Kilopi
An Enceladus temperature map is here. The accompanying article describes the theory that we're seeing internal heat (probably tidal) which is being more efficiently transferred through the thin, venting crust at the pole. Elsewhere, the ice is thicker, providing better insulation.
Information on Saturn's poles is here, describing the atmospheric processes that cause the high temperatures.
Looks like my top-of-the-head list wasn't too far wrong.
Grant Hutchison
Established Member
If you read space.com, it's because there are primordial black holes in the center of Jupiter and Saturn.
Established Member
No, it was just a question. I thought that was what the "Questions and Answers" section was for.Bold Mine:
The way you worded this implies that 'current theory' is somehow faulty that it overlooked this.
Maybe so. That's precisely why I asked the question, to see if anyone knows what the "other factors" might be.
Let's start with Saturn and Enceladus.
Sorry, I should have asked: "Does anyone know how we can account for this?
Banned
No problem- but that's why sometimes things need to be addressed...
Established Member
It certainly wasn't!An Enceladus temperature map is here. The accompanying article describes the theory that we're seeing internal heat (probably tidal) which is being more efficiently transferred through the thin, venting crust at the pole. Elsewhere, the ice is thicker, providing better insulation.
Information on Saturn's poles is here, describing the atmospheric processes that cause the high temperatures.
Looks like my top-of-the-head list wasn't too far wrong.
Grant HutchisonThanks for the references. We're reading the same sort of articles. I simply note the surprise at the observations which is expressed by the scientists working on the projects and which necessarily makes their first-guess explanations something less than completely convincing. And what about the other gas giants, Neptune and Jupiter, which are also mentioned in your second reference? Are we to believe that it's the same physical laws/forces which are at work everywhere or do we have to find some kind of ad hoc explanation for each individual case?
Established Member
Precisely!
Order of Kilopi
Surprise is to be expected when you're dealing with complex systems you've never seen before.
Your use of the words "guess" and "ad hoc" rather belittle the process going on: an unpredicted observation is made, all the relevant data are reviewed, and a testable hypothesis based on sound physical principles is framed. It's science, caught in the act.
We can safely assume that different process will be occurring in gas giants and icy moons, but that some gas giants may resemble other gas giants, and some icy moons may resemble other icy moons. So I'd imagine we'll end up looking at a limited repertoire of different processes, repeating across similar environments.
Grant Hutchison
Order of Kilopi
Earlier hypotheses -- I don't know how they have faired -- included a roll, as reported in Universe Today: Saturn's Moon Enceladus Rolled Over:
(Nature: Diapir-induced reorientation of Saturn's moon Enceladus, Nimmo et al)Rotating bodies, including planets and moons, are stable if more of their mass is close to the equator. "Any redistribution of mass within the object can cause instability with respect to the axis of rotation. A reorientation will tend to position excess mass at the equator and areas of low density at the poles," Nimmo said. This is precisely what happened to Enceladus.
Order of Kilopi
Ah, that's neat. Thanks.
It makes the polar location part of the process.
Grant Hutchison
Established Member
Warm Poles
All four of the gas giant planets radiate more heat than they receive from the sun. So in all 4 cases there is nothing at all questionable about the poles being warm, since the sun does not dominate the heating of the atmosphere. It should not be surprising that the poles look warmer, which might be accounted for in any number of ways. For instance rapid rotation will spread heat energy over a wider area near the equator, but concentrate it over a smaller area near the poles. It might also be the case that over the poles we can see deeper into the atmosphere, where it is warmer. It is also possible that, since the planets are all flattened by rotation, the poles are simply closer to the center and therefore warmer. That last one probably is not important for the planets, but it is extremely important for rapidly rotating stars, which are significantly hotter at the poles.
As for Enceladus, it has a collection of strong jets at one pole. We don't know for sure why it has jets, but it does seem that the shear component if tidal stress can explain the observed "tiger stripe" features and jets. See, i.e., Smith & Pappalrdo, 2007a; Smith & Pappalardo, 2007b; Nimmo, et al., 2007a; Nimmo, et al., 2007b. But as pointed out in Roberts & Nimmo, 2008, this may require the assumption of a transient subsurface ocean on Enceladus.
Order of Kilopi
Also, in the case of the terrestrial planets, the atmospheric circulation is the primary factor in the temperature difference, ranging from a very small effect (mars) to a massive circulation to the point where there is no significant temperature variation over the whole planet (Venus). The factors for this are simply that the thicker the atmosphere, the more heat is transferred to the poles, and the slower the planet rotates, the more efficiently it can do so (fewer circulation cells). This is somewhat oversimplified, but will do as a simple explanation for the terrestrials.
As previously mentioned, the Jovian planets have a significant amount of internal heat involved. They also have atmospheric circulation, which is significant, but less important on the Jovian planets than the terrestrials overall.
Established Member
From my reading of the Roberts & Nimmo, 2008 abstract, the requirement that the hypothesised subsurface ocean be "transient" is simply another way of saying that the currently observed physical characteristics of Enceladus are completely incompatible with the existence of a subsurface ocean, which can only be "a relic of an earlier era of greater heating". There is thus apparently the need to postulate that in the very recent past (recent because otherwise the subsurface ocean would have had time to freeze again), Enceladus was on a considerably more eliptical orbit than is the case today.
Would that be a correct reading?
Banned
Planets whose axes are heavily tilted off the plane of the ecliptic might have a pole completely exposed to nearly-overhead sunlight, as well, producing relatively balmy conditions compared to the rest of the planet...
...until it's orbit is half-way around the sun and the same becomes true of the other pole.
Established Member
Did you have a particular planet in mind and does the available temperature data confirm your idea?
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