What Cassini heard from Huygens as it descended to Titan's surface is now available as an audio file from the European Space Agency, but it may be easier to download it from Ralph Lorenz' home page. Lorenz is an assistant research scientist at the University of Arizona's Lunar and Planetary Laboratory and a co-investigator on Huygens' Surface Science Package; he created the sound file based on Cassini data. The file compresses four hours of real-time audio into about a minute. What the listener hears is a tone whose frequency depends on the strength of the Huygens signal as received by Cassini. The probe's antenna emitted radio energy unevenly, "...like the petals of a flower rather than the smooth shape of a fruit," as Lorenz puts it. As the probe's orientation changed durings its long descent, its spin rate slowed, causing rapid changes in the tone. "You can hear how the motion becomes slower and steadier later in the descent," Lorenz said. A UA press release on Lorenz' work can be...

Only time and energy for an abbreviated post today -- I'm down with the flu! But Cassini comes through in the pinch. Below is a spectacular image of Mimas seen against the blue northern latitudes of Saturn. From the JPL description (more of which can be found here): Mimas drifts along in its orbit against the azure backdrop of Saturn's northern latitudes in this true color view. The long, dark lines on the atmosphere are shadows cast by the planet's rings. Saturn's northern hemisphere is presently relatively cloud-free, and rays of sunlight take a long path through the atmosphere. This results in sunlight being scattered at shorter (bluer) wavelengths, thus giving the northernmost latitudes their bluish appearance at visible wavelengths. At the bottom, craters on icy Mimas (398 kilometers, or 247 miles across) give the moon a dimpled appearance. Image credit: NASA/JPL/Space Science Institute.

One way to explain the existence of the Moon is through a giant collision, one that tore off enough material to build a satellite in a planetary orbit. Can Pluto and its moon Charon be explained the same way? Robin Canup thinks so. Canup is assistant director of Southwest Research Institute's Department of Space Studies; she argues the case in the January 28 issue of Science. The Moon may seem large in our skies, but it makes up only about 1 percent of Earth's mass. Charon, on the other hand, is 10 to 15 percent the mass of Pluto, which suggests to Canup that the corresponding collision must have been with an object almost as large as Pluto itself. She also believes that Charon probably formed intact as a result of the collision. "This work suggests that despite their many differences, our Earth and the tiny, distant Pluto may share a key element in their formation histories. This provides further support for the emerging view that stochastic impact events may have played an...

Exactly how big is the Solar System? We used to talk about Pluto as the outermost planet, implying the Solar System ended when you crossed its orbit. Now we talk in terms of the Kuiper Belt, a band of debris and planetesimals far beyond Pluto's orbit; beyond the Kuiper Belt looms the vast Oort Cloud, a spherical halo of comets that may extend a light year from our Sun. And if one thing is clear from current research, it's that our old notions of boundaries have to be readjusted. Take recent work at the Southwest Research Institute, which shows that the process of planetary formation once extended far beyond the orbit of Pluto. As reported in the January 2005 issue of The Astronomical Journal, SwRI's Alan Stern used planetary formation software to explore how objects like Sedna, a huge planetoid fully 2/3 the diameter of Pluto, could have formed at distances from 75 AU to 500 AU. The two distances represent Sedna's closest approach and farthest distance from the Sun. "The model...