CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Cosmic Blasting Zone

Cosmic Blasting Zone
PIA 07761

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  Impact-pummeled Hyperion stares back at Cassini in this six-image mosaic taken during the spacecraft's close approach on September 26, 2005.

This up-close view shows a low density body blasted by impacts over the eons. Scientists originally believed that the spongy appearance of Hyperion is caused by a phenomenon called thermal erosion, in which dark materials accumulating on crater floors are warmed by sunlight and melt deeper into the surface, allowing surrounding ice to vaporize away.

Cassini scientists now think that Hyperion's unusual appearance can be attributed to the fact that it has an unusually low density for such a large object, giving it weak surface gravity and high porosity. These characteristics help preserve the original shapes of Hyperion's craters by limiting the amount of impact ejecta coating the moon's surface. Impactors tend to make craters by compressing the surface material, rather than blasting it out. Further, Hyperion's weak gravity, and correspondingly low escape velocity, means that what little ejecta is produced has a good chance of escaping the moon altogether.

At 270 kilometers, (168 miles) across, Hyperion's impact-shaped morphology makes it the largest of Saturn's irregularly-shaped moons.

Six clear filter images were combined to create this mosaic. Images were taken by the Cassini spacecraft narrow-angle camera at a mean distance of about 33,000 kilometers (20,500 miles) from Hyperion and at a Sun-Hyperion-spacecraft, or phase, angle of 51 degrees. Image scale is 197 meters per pixel.

[Caption updated February 12, 2008]

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, visit and the Cassini imaging team home page,

Credit: NASA/JPL/Space Science Institute
Released: December 6, 2005 (PIA 07761)
Image/Caption Information

Alliance Member Comments
Mercury_3488 (Feb 16, 2008 at 7:57 AM):
I've sometimes wondered about this also.

Hyperion is the least dense of the known solid bodies in the entire solar system, only 0.55g cm3. This suggests a rubble pile held together by gravity & / or a more coherent body with huge internal voids.

My bet is the rubble pile. Like polystyrene, it is possible to punch deep but narrow holes in it. We see similar here on Hyperion.

I had seen one suggestion bantered about elsewhere (not my idea), that Titan formed in a heliocentric orbit at one of Saturn's lagrange points & over time, Titan was drawn towards Saturn. Hyperion was suggested to be Titan's former moon.

The mass ratio between Hyperion & Titan is identical to that of Dione with Polydeuces & Helene as well as Tethys with Telesto & Calypso. These facts were part of a thought exercise elsewhere.

Hyperion being a former comet is an interesting idea. Remember that Phoebe is almost certainly a captured comet / KBO.

Also remember the floors of these deep craters are dark, so they absorb the very little solar energy there is & can burn through the ice.

I am sure there are a whole multitude of reasons for Hyperion's weird situation. A most fascinating object.
Harry (Feb 15, 2008 at 4:28 PM):
Of all the Cassini images, this is the one I keep coming back too. Somehow, I wonder if Hyperion is a not a normal (whatever that is) cratered moon but, it is a burned-out comet. The density of craters seem to put Hyperion out of place. Hyperion has preserved evidence of many more craters that other bodies in the region. Maybe it is much older or from a differnt part of the solar system closely resembling a shooting gallery.

I wonder if Hyperion is actually a comet that was captured by Saturn. The craters might actually be vents from when the comet was active. The steep, straight sides of the craters/vents might be determined by the angle of repose of the ejecta material coming from the vent that did not attain escape velocity. Or, maybe the geometry of the vents is normal as they slow-down and freeze after an active cycle. The dark material in the bottom of the "vents" might be carbon-rich material from the interior of the comet. Also, the dark material could have higher density than the volatiles that escaped the vent or be higher mass "pebbles" that accumulated at the bottom of the vent.

Hyperion has so low a density as to suggest that it is porous. The interior cavities may be the voids left by the volatiles that escaped the body while it was active during passes through the inner solar system. These residual cavities might not have collapsed as the comet evolved. They may have collapsed later when the interior was shocked by a metor impact. Hyperion's irregular shape may be determined by the later cave-ins. The morphology of the cave-ins might correlate to how the volatiles had accumulated during the genesis of the body that is now Hyperion.

If Hyperion is the nucleus of an old comet, Saturn may have caught it while it was still active from a pass by the sun. If it was still venting while in orbit, it could be a source of the material in Saturn's rings.

Anyway, this is a lot of conjecture. A hand-full of pictures and a few scientific measurements have generated a myriad of question. I think this is wonderful.
Acrylikhan (Dec 5, 2007 at 6:00 PM):
I love this image. even in black and white, there so much texture and depth! I am glad you guys were able to capture it!