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Unmanned Spaceflight.com _ Jupiter _ A common mass scaling for satellite systems of gaseous planets
Posted by: AlexBlackwell Jun 14 2006, 05:46 PM
Canup and Ward have a new, interesting paper ("A common mass scaling for satellite systems of gaseous planets") in the June 15, 2006, issue of Nature. See the http://www.nature.com/nature/journal/v441/n7095/edsumm/e060615-09.html for more details.
Posted by: ljk4-1 Jun 14 2006, 06:15 PM
For another related reference:
http://www.unmannedspaceflight.com/index.php?s=&showtopic=2637&view=findpost&p=51307
Posted by: AlexBlackwell Jun 15 2006, 12:11 AM
A related press release: "http://www.swri.org/9what/releases/2006/Canup.htm."
Posted by: tasp Jun 15 2006, 01:50 AM
The mass ratios of Titan to Hyperion, Tethys to it's co-orbitals, Dione to its co-orbitals, possibly Mimas to the Herschel impactor, and possibly Callisto to the Valhalla impactor are all around (IIRC) 5000 to 1.
Weird, huh?
Posted by: Bob Shaw Jun 15 2006, 09:10 AM
Weird, huh?
There's probably some reason for it, with orbital mechanics associated with all sorts of factors 'boiling off' everything other than a strictly limited range of masses relative to their 'primaries'. You'd end up selecting for some mass ratio or other...
Bob Shaw
Posted by: Thorsten Jun 15 2006, 01:38 PM
Quite striking that the total mass of all regular satellites of a gas giant appears to be close to 1/10’000 of the planet mass!
If this also holds true for exoplanets, which are considerably larger than Jupiter, than one would need a gas giant, weighing as much as 10’000 Earths or 30 Jupiters, for one Earth sized moon (given a planetary system like Saturn, where a single large moon comprises almost the complete mass of all moons).
However, wouldn’t such a 30 Jupiter- mass world be already quite deep into the realm of brown dwarfs, by having more than twice the assumed limiting mass for thermonuclear fusion of deuterium? Don’t know what this means for the habitability of this moon.
Would such a 30 Jupiter mass-range world radiate a lot of thermal energy – at least in its infancy? Would that be sufficient to boil away the moon’s water?
Posted by: Rob Pinnegar Jun 15 2006, 02:31 PM
This is an interesting point, especially when comparing the relative sizes of the major satellites in the Jovian and Uranian systems: two good-sized ones closer in, two somewhat bigger ones further out. (Saturn's system, in a way, is a hybrid: it resembles Uranus' with a Galilean thrown in for good measure).
Is Neptune omited from this argument (even though Triton roughly follows the pattern)?
Posted by: AlexBlackwell Jun 15 2006, 05:30 PM
Primarily, Canup and Ward use Jupiter, Saturn, and Uranus and their coterie of satellites in their model, though they do consider Neptune. From the paper (references omitted):
"Although the model presented here applies to regular satellite formation, it is remarkable that Neptune's single large, irregular satellite, Triton, also contains a similar mass fraction, with M(Triton)/M(P) ~ 2.1 x 10^-4. Triton's orbit is retrograde and inclined, and it is believed to have been captured intact from heliocentric orbit. Although we lack direct evidence of a putative original prograde neptunian satellite system, it seems clear that it cannot have contained much greater total mass than Triton itself. Otherwise, a retrograde and initially eccentric Triton would have been destroyed while traversing the regular satellite region (either as it was accreted or collisionally disrupted, or by the decay of its orbital angular momentum36 owing to interactions with a much greater mass in prograde material). The survival of a captured retrograde satellite requires it to have comparable or greater mass than any prograde system with which it actively interacts. As larger interlopers would have been less numerous (and therefore captured less frequently), the most probable surviving Triton-like object would be one having the smallest mass affording its survival, which would suggest that M(Triton) is similar to the total mass of Neptune's original regular satellites, or M(T)/M(Neptune) ~ O(10^-4) as well."
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