[X] My Assistant

[Guest_Sunspot_*]

A nice shot of Hyperion

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=33556

[Decepticon]

This moon is very diffrent looking compared to the other smaller moons.

Could this moon be broken chunk off another sat?

[Guest_BruceMoomaw_*]

They think that unlikely, but they DO think that something big hit Hyperion itself and blasted a lot of material off it (most of which then probably hit Titan).

That irregular shape gives Hyperion another peculiar distinction -- since it's in a pretty eccentric orbit close to Titan's (with an exact 3:4 period ratio), Titan's periodic tuggings acting on its irregular shape mean that it rotates in a completely chaotic way. That is, not only its rotational period but its rotational direction keep changing in a virtually completely unpredictable way: it speeds up and slows down, tumbles in different directions, and sometimes even reverses direction! As that very great SF writer Poul Anderson pointed out in one of his last stories ("Scarecrow"), this means that landing on it will be unusually difficult -- the surface will keep sliding around at a fair speed underneath your descending ship in a way that cannot be predicted from one moment to the next. So far it's the only chaotically rotating moon we know of in the Solar System: there were some initial suspicions that Neptune's moon Nereid might be one, but more recent measurements suggest that it may have a regular (if non-synchronous) rotational period after all.

That chaotic tumbling also seems to have caused Hyperion itself to be coated over its entire surface with dark material similar to that on the leading side of Iapetus (and probably coming originally from Phoebe or one of the other little irregular moons) -- Titan apparently intercepts all the remainder of this inward-spiralling stuff before it can reach any of the light-colored inner moons.

It is arguably the fourth oddest of Saturn's moons, and it will be interesting to see what Cassini makes of it during its one close flyby in late September.

[Decepticon]

I hope we get a good look at most of the surface. Full surface mapping of all major moons is something I'm looking forward to.

[Gsnorgathon]

I keep thinking Hyperion's got an interesting story to tell, if only someone can figure out how to get it to talk to us...

Does anyone here know if there's a consensus on the origin of Hyperion's eccentric orbit? Would a more-or-less spherical Hyperion have been pumped up into its current orbit by Titan, or is the eccentricity the result of whatever whacked it into its current odd shape?

[MiniTES]

It is arguably the fourth oddest of Saturn's moons,

After Titan, Iapetus, and.... is Enceladus or Pheobe your third oddest? Just curious.

[Guest_Sunspot_*]

http://www.planetary.org/saturn/hyperion.html

We have one close flyby of Hyperion - not too far off either, Setpember 26, 2005, altitude 1000km.

[Guest_BruceMoomaw_*]

"After Titan, Iapetus, and.... is Enceladus or Pheobe your third oddest? Just curious."

Actually, I'd tie Iapetus and Enceladus for second. We now know Phoebe to be just the biggest member of a veritable cloud of small captured irregular satellites, which are probably very similar to the captured irregulars that we now know orbit Uranus and Neptune. After Hyperion, I'd probably rank the Janus/Epimetheus pair, those perpetually starcrossed -- or orbit-crossed -- lovers which are obviously the two pieces of a single moon that got cracked in two by a major impact (or perhaps into more fragments, which later re-coalesced into two rubble piles). By the way, J. and E. will carry out one of their every-4-years orbital altitude exchanges this year.

JPL seems to feel the way I do. In 1997 they prioritized Cassini's flyby targets besides Titan as follows: Enceladus, Iapetus, 2nd Enceladus flyby, Dione, Hyperion, Rhea, 3rd Enceladus flyby.

[Bjorn Jonsson]

http://www.planetary.org/saturn/hyperion.html

We have one close flyby of Hyperion - not too far off either, Setpember 26, 2005, altitude 1000km.

There is also a 166,000 km Hyperion flyby on June 11.

[Gsnorgathon]

Which ought to provide slightly better than 1km resolution, if I'm doing the math right. Voyager 2's closest approach was 431,370km.

[Guest_Sunspot_*]

Another look at Hyperion:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=35559

[Decepticon]

This moon has just been a pain to get a nice pic of.

Looking at this image and Voyagers I expect this moon to have big surprises.

[Decepticon]

Guys, Gals check this out!

Not bad...

http://ciclops.lpl.arizona.edu/view.php?id=904

[Guest_Sunspot_*]

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=35611

More Hyperion

[Decepticon]

Here's a update. http://photojournal.jpl.nasa.gov/catalog/PIA06623