What's up in the solar system for the week of May 12
It's time to check in on what's going on with our trusty robots around the solar system.
At Saturn, Cassini just completed its 44th targeted flyby of Titan, which (for historical reasons) is called "T43." This flyby included RADAR imaging of the Xanadu region, which I'm very much looking forward to seeing. Immediately after the flyby, Cassini crossed the ring plane to the north (unlit) side, where it'll be for most of the rest of the week. The orbits are now very quick at 8 days apiece, almost one per week, so Cassini will be at apoapsis again by Wednesday (beginning Rev 68) and then at periapsis again on Saturday. No targeted flybys or more distant approaches to the major moons will occur this week. Last week's raw images included many images that could be assembled into a polar movie on Saturn, lots and lots and lots of shots of various parts of Saturn's ring system (facilitated by Cassini's high-inclination orbit, which gives the spacecraft a good vantage point onto the rings), frame-filling and more distant color views of Tethys, and, most recently, more than 500 frames for a movie of spokes in the B ring (facilitated by Cassini's high-inclination orbit). Anybody want to try making a little animation of part of this? Last week's image releases all focused on shepherd moons, shadows on the rings, and two shots of Rhea, plus this beautiful close-up of spiral density waves in the rings.
NASA / JPL-Caltech / SSI
Spiral density waves in Saturn's rings
The presence of small moons near Saturn excites a variety of wavelike formations in Saturn's rings. Because parts of the rings closer to Saturn circle the planet faster than parts of the rings farther from Saturn, these waves get sheared out until they wrap repeatedly around the planet, forming a tightly wound spiral. In an individual Cassini photo, the spiral appears like a set of parallel rings with decreasing width. This photo was taken on April 1, 2008 while Cassini was on the sunlit side of the rings. It has a scale of approximately one kilometer per pixel.
NASA / JPL-Caltech / UA / Eduardo Tesheiner
Spirit route map to sol 1466
On the surface of Mars, it is late autumn in the southern hemisphere (Ls 71°), sol 1,549-50 for Spirit and sol 1,528-9 for Opportunity. Spirit is still parked on the edge of Home Plate, in the same position it has occupied since sol 1,464 (February 15), with its solar cells pointed northward toward the winter sun. Opportunity is sitting on the slope of Duck Bay, with its wheels dug in to a patch of sand, diagnosing a problem with the shoulder joint on its robotic arm. The May 7 weather update from the MARCI camera on Mars Reconnaissance Orbiter reported "benign" weather conditions around much of Mars this past week, with "partly cloudy skies but no dust activity" for the rovers. And Phoenix is getting closer, now only 13 days from landing.
There were some neat images from the Mars Odyssey mission last week, including ones of the bright band of clouds at the edge of a dust storm and two each showing the tongue-shaped deposits of landslides and of isolated fields of sand dunes. Mars Reconnaissance Orbiter mission released views of ancient, mantled craters (whose ejecta blankets now host lots of dark dust devil trails); some views of frosty patterns in near-north-polar regions; layered rocks on the flanks of Olympus Mons and Noctis Labyrinthus; and a nice fresh rayed crater in the Tharsis region. Their site seems to be particularly slow this morning, perhaps because of their invitation issued last week to visitors to search for Mars Polar Lander, something I'll have more to say about later this week. There was nothing new from Mars Express last week.
At the Moon, Chang'e 1 and Kaguya are currently in orbit. Nothing new was released from either mission last week, though you should check out, if you haven't already, the almost-high-def videos I posted here. At Venus, Venus Express is currently in orbit. Nothing was released last week from that mission either.MESSENGER is cruising toward its second encounter with Mercury on October 6, 146 days away. It is 156 million kilometers from Earth and 120 million kilometers from Mercury. Over the last three weeks they've released new images on Monday mornings, so maybe this is a new pattern (and one that's conveniently timed for this roundup). Last week's image was a closeup frame on the "spider," now named Pantheon fossae, and this week's was a view of Bashō crater, which was spotted first in Mariner 10 photos, easy to see because of its dark rim and bright rays.