Enceladus might have a saltwater ocean

Frank Postberg (Max Planck Institute, Germany) has a Nature letter on Cassini's detection of sodium salts in Saturn's E ring; see also this press release. This is a very interesting result, because it implies that Saturn's satellite Enceladus might have a liquid water ocean beneath its icy surface. Recall that in 2005, the Cassini spacecraft spotted geysers shooting tiny ice crystal from cracks in Enceladus' surface (pictured). Those ice grains go into orbit about Saturn and form that planet's tenuous E ring. During subsequent passages through the E ring, Cassini's dust detector was then used to determine the composition of those ice grains, and found them to contain salt at the 1% level. Because those ice grains originated inside Enceladus, Postberg and co-authors argue that these grain's high salinity is possible if, under Enceladus' ice, there is also a liquid ocean there that lies on top of a rocky core that is the source of the salt. Note that there is also an astrobiology angle here, too, since if Enceladus is warm enough to maintain a liquid water ocean, then there is also the possibility for ocean life there, too.

Shadows along the Keeler Gap

This Cassini image is looking towards the outer edge of Saturn's main A ring. The dark band near the ring's outer edge is the Keeler gap, which is maintained by the small 8km satellite Daphnis, which is the white speck there that casts a shadow across the ring plane. Daphnis' orbit is also inclined slightly relative to the ring plane, which carries it above/below the ring plane with each orbit about Saturn. Due to this up/down motion, Daphnis' gravity on the ring also pulls the nearby ring material at the gap's edge up/down by about 1 km. And because Saturn is near its equinox, the Sun's illumination here is almost horizontal across the ring plane, causing these km-high piles of ring particles to appear brightly lit on their sunward side, which also casts shadows across the ring plane. Check the Cassini/CICLOPS website for more details, or the recent paper in AJ by Weiss et al (subscription required).

Shadows cast by disk-embedded planets

A recent theory paper by Hannah Jang-Condell (U. Maryland) examines the shadows that might be cast by recently-formed planets as they orbit within the circumstellar disk in which they formed. Her numerical models show that the planet's gravity will 'depress' the disk there. If that disk were then viewed by an astronomer at optical wavelengths, then that depressed spot would resemble a dark pothole, since that depression is not illuminated by the central star (see Figure). The exception is at the pothole's far side, which would instead appear as an illuminated bright spot. Note that extra-solar planets are difficult to see via direct imaging. However this work suggests a new technique that might be used to discover unseen planets indirectly---by searching for these planet's darkened potholes and dimples that they create in a planet-forming disk.

Mars landers:destroying the organics they were sent to find?

Even if there is no life present on Mars, that planet should have organic molecules on its surface, due to impact delivery by asteroids and comets, which are known to contain organic carbon-bearing molecules. However, organics have not been detected by any landers sent to look for these materials---not by the Viking landers, nor by the more recent Phoenix lander. Organics are detected by heating soil samples in an onboard oven, and looking for their signature in the gases released during heating.

However, Douglas Ming (Johnson Space Center) and colleagues note that the Martian surface contains perchlorate salt, which releases oxygen when heated. Ming's experiments also show that this released oxygen might then burn up any organics present in the soil samples. So if Ming's thinking is correct, this might explain why the Martian landers have not detected organics on Mars---their detection methods might have been burning up the organics that they seek. For more information, see this New Scientist article, as well as Ming's LPSC abstract.

Split Comet Schwassmann-Wachmann 3

Comet Schwassmann-Wachmann 3 broke up into several fragments in 1995. Its orbit period is 5.4 years, so came closest to the Sun again in 2001 and 2006. Bill Reach and colleagues used the Spitzer Space Telescope to observe this comet in infrared wavelengths in May 2006. The faint band connecting the fragments is a trail of debris that traces their orbit about the Sun. These astronomers detected 55 fragments along this comet's orbit, several of which are seen above. The color image of two brighter components show their dusty tails in red with a hint of green to show that CO2 gas is emitted from the sunward-facing parts of the comet nuclei. These fragments comae and tails are generated as the icy cometary nuclei warm and sublimate (evaporate) in the sunlight, whose weak pressure also sweeps the dust away in the anti-sunward direction. A preprint by Reach et al on these Spitzer observations is also available.

Shuttle transits the Sun

Space Shuttle Atlantis was photographed in silhouette against the Sun on May 13th by French astrophotographer Thierry Legault, while in Florida. The shuttle's transit across the Sun lasted only 0.8 seconds, and this picture was taken before the shuttle caught up with Hubble. See Legault's website for other other very nice astronomy pictures.

Girl who named Pluto dies at 90

Venetia Phair, UK, was 11 when Pluto was discovered by Clyde Tombaugh at the Lowell Observatory in 1930. Her grandfather, Falconer Madan, told her of the discovery, and discussed possible names for the new planet. ‘Why not call it Pluto?’, she suggested. Madan passed the suggestion on to friend Herbert Hall Turner, professor of astronomy at Oxford, who in turn telegraphed Lowell Observatory, which endorsed the suggestion. Venetia's grandfather gave her a five-pound note for her idea. Venetia died April 30 in her home in Banstead, England.