... enigmatic moons. Cassini will fly by Phoebe, Saturn's largest outer moon, ... opportunity during the mission to study Phoebe at close range," said Dave Seal, ... Laboratory (JPL), Pasadena, Calif. ...
... Cassini mission reveal Saturn's moon Phoebe has more planet-like qualities ... had their first close-up look at Phoebe when Cassini began exploring the ... and geology, scientists found Phoebe was ...
... 2005FEATURES ON SATURN'S MOON PHOEBE NAMEDTwenty-four of the largest craters on Phoebe, the small, retrograde outer moon ... Astronomical Union.Two image montages of Phoebe, the first stop in the ...
As it entered the Saturn system, NASA's Cassini spacecraft performed its first targeted flyby of one of the planet's moons. On June 11, 2004, Cassini passed Phoebe, the largest of Saturn's outer or "irregular" moons, at an altitude of just 1,285 miles (2,068 kilometers).
Phoebe looks like target practice for the solar system. Looking at the various pictures and by observation, it appears that the craters begin to "fill in" faster than other craters on other moons in the solar system. Am I imagining this or is there something to what I see?
Yes I agree, Hyperion is very curious. One idea is that the deep fluted craters are due to normal craters being deepened by the dak dusty floors absorbing what little sunlight is out here & 'burning' a deeper hole, giving Hyperion the peculiar sponge like appearance. Also Hyperion is the least dense 'solid' body at only 0.55 Gcm3, just over half that of solid H2O ice, suggesting that Hyperion is an icy rubble pile held together by gravity. Certainly sopme asteroids are like this, main belt asteroid 253 Mathilde certainly so, rather carbonaceous materials rather than ice, the Mars moon Phobos (possibly Deimos too) & the Jupiter moon Amalthea. Phoebe appears coherent as does the main belt asteroid 21 Lutetia, so not all 'small' bodies are rubble piles, but Hyperion almost certainly is. Whether or not Hyperion is a captured comet is open to question, where as Phoebe most certainly is. Shame we cannot get another close pass of Phoebe, but I think we will see Hyperion again with Cassini.
Do we know when yeaterday's Rhea imagery will be avaliable? Hope Cassini has not gone into safing.
Myself I would rather use any excess fuel for a close pass of fascinating Dione or Mimas or one of the lesser known inner moons like Prometheus, Pandora, or a co orbital like Helene, Ploydeuces, Telesto or Calypso. We have had loads of Titan & Enceladus, so a close pass of one of the lesser known ones would be nice. Shame we cannot do Iapetus or Phoebe again, as far too far out.
thanks carolyn, given that you are correct, of course, 'thermal' would not necessarily mean a volcanic eruption. Interesting also that you mention, in how the dust ring about Phoebe being of keen interest as well, I imagine that particular interest may be for a number of reasons also!
mipsandbips: But there's no evidence for a massive volcanic explosion. If that were the case, you'd see craters that were partially buried. And the pattern wouldn't necessarily look like what we see. Computer models have verified that general outline you would see from a dust-initiated thermal runaway effect, and they agree beautifully with the observed pattern. Finally, a dust ring has just been found associated with Phoebe, an outer Saturnian satellite. That dust is making its way into Iapetus' orbit. So all holds together beautifully.
Although Phoebe orbits Saturn in a retrograde direction, looks like the rotation on the axis is prograde.
Will be very interesting indeed to compare the fantastic Cassini Phoebe encounter with the New Horizons imagery & spectra of the Pluto moons Nix & Hydra (though Phoebe is very much larger than both).
I still reckon Cassini beat New Horizons to imaging a KBO in close up. Unless we think Triton is a captured KBO by Neptune, then Voyager 2 wins.
Eris, Triton & Pluto (that order of descending size & mass), still to me appear to share a common origin in the Kuiper Belt, just that Eris & Pluto are the largest. Does Phoebe share a common origin too with them??
Thank you very much John.
Yes I also think that Titan's rotational axis is perpendicular to the orbital plane. I can see that the difference in dates is only a matter of a few weeks at most.
20' of arc difference in rotational axis, that is very minor even in a 29.5 year long 'year'.
I have run the sequence through Redshift 5 & the 11th August does indeed match up with Saturn & the Titan Equinox appears to be on the 5th August, so about a week ahead of Saturn's.
If you are interested, I ran through the Equinox for Iapetus with a fairly large inclination of 14 degrees 45' & the equinox occurred way back on 31st March 2007, 19 months ago already!!!!!!! Also did Phoebe, Equinox was even further back on 1st September 2006. So for these two, Northern Spring began quite a while ago already.
Looking forward to seeing the rest of the images, particularly the close up SKEET ones.
What a good luck that Phoebe was so closed to Cassini when the spacecraft approached Saturn - this encounter was before SOI and no other flybys of Phoebe are planned. Even no ones in the Extended Mission. If Phoebe had been at its opposite point of its orbit then this Image would not have been possible. Cassini made a fantastic engineering action obtaining this image with no image smear ! This Image shows that even rather small Phoebe has got a complicated history of its surface, I suppose.
That is Phoebe in full view ! It appears to be a primitive, unmodified body captured by Saturn. Because of its actual orbit. It is ice-rich because it appears bright. But it has got also a coating of darker material. I think it was a Trans-Neptunian Body, an icy 'planetesimal' , before having been captured. It's the smallest Saturnian satellite that is 'mid-sized or large' by my classification.
Saw this once before as a shadowy noisey raw image. It's great to see that some of the smaller moons are also being researched like Hyperion, Janus, Epimetheus, Helene, Telesto, Phoebe, etc.
Wonder if Janus is like Epimetheus, an icy rubble pile held together by gravity?
Does anyone know when the Helene encounter will be? Is there any chance of a close passes of Calypso, Telesto (again) Polydeuces, etc?