Monday, July 11, 2005

Hyperion Rev09 Releases

CICLOPS has released an anaglyph and a movie of images taken of Saturn's spongy moon Hyperion last month. These images show newly resolved features on these, the highest resolution images ever taken of Hyperion. Unfortunately, many of these images were over-exposed, but they still provide plenty of insights into the processes that have taken place on this small moon. Among the notable features is Hyperion's irregular shape. Hyperion is rather large for an irregular satellite, 328 by 260 by 214 km (dimensions given in the caption are the radii values). This has led some to suggest that Hyperion may be the remnant of a larger satellite that was torn to pieces by an impact and failed to coalesce back due to tidal interactions with Titan. While these images don't go either way on this issue, it does show signs that Hyperion has trouble re-accreting material from impacts on it surface. Many of Hyperion's craters are strangely formed, often with dark material within their floors and bright material along the walls and rim. Titan's gravity, in addition to causing impact ejecta to not fall back on Hyperion, may also cause Hyperion to tumble as it orbits Saturn.

The sponge-like appearance of the surface is followed to the interior, where signficiant porosity has led to a very low density body, with a density of only 0.6 g/cm3, based on pre-flyby, but Cassini NAV mass values. This also suggests that Hyperion is likely made up of nearly pure water ice, with components that make up the dark material seen on crater floors constituting very little of the interior, otherwise, pore space within Hyperion could make up 50% or more of the interior.


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