Too much outer planets news for me to read (much less report on)
Posted by Emily Lakdawalla
04-05-2006 20:51 CDT
Naturally, on a day when I have two conferences I should be attending (haven't figured out how to clone myself yet, unfortunately), there were also about half a dozen announcements of cool and interesting new science findings or events, and the conference I attended had no wireless network set up so I was unable to read any of it, much less post about any of it. I'm already in a hole it's going to take me weeks to dig out of!
So before I get to my notes from OPAG I want to minimally acknowledge today's news, which I'll have to get to in more detail later. They released new SAR images from the latest Titan flyby -- you can see those at Photojournal (actually I do have a bit to say about those below). Ralph Lorenz's paper on the dunes on Titan as seen in previous RADAR images came out in Science. The Cassini mission released something about a new calculation of the day length on Saturn. ESA, NASA and the University of Arizona released a new video visualization of the descent of Huygens. The Space Telescope Science Institute released new Hubble images of the new red spot on Jupiter.
It was a really good day for outer planets news, and dang if I wasn't sitting in a room containing a sizable fraction of the outer planets science community, whom I could have asked for more information about these things; but I was Internet-less so had no idea about any of them! Except for those new RADAR images. Those, I saw, because Steve Wall (deputy team leader on the RADAR instrument) came down at lunchtime with a 10-meter-long printout of the entire new swath. I was salivating.
As with all previous SAR swaths, this one contains whole regions that don't look anything like the previously captured ones. Its western end covers part of the dark region now called Shangri-La, including Shikoku Facula ("Great Britain") and Guabonito, a small circular feature. Guabonito looks similar in RADAR to what it looks like in the infrared images (only more detailed), but in Shikoku there's a dark spot that is completely invisible in the infrared, making the northern part of Shikoku look very impact-crater-like. In fact, there are quite a lot of things that look like degraded impact craters in this swath. Nothing like the totally obvious impact features in T3, but still, it's hard to make a ridgy ringed structure surrounding a central flat region or depression in any other way than by impact cratering.
Xanadu occupies the center of the swath, and it appears to be very mountainous. I squinted and stared at those mountains and couldn't make them line up into ranges of mountains, which makes it hard to guess what made them. It's just a vast region of very peaky-looking terrain without any particular pattern to it as far as I could see; hopefully the RADAR team can make more sense of it. Xanadu appears to be cut by lots of drainage features, though to my eye the channels seemed to meet at angles I didn't expect. Someone told me that they thought the channels looked pretty strongly structurally controlled; someone else said it's hard to say really what they look like, since they are at the lower end of the size range that this data can resolve. There were several things that looked pretty clearly like degraded craters within Xanadu. Several Europa folks were staring at the picture and musing about the fact that there is absolutely nothing in this or any of the other RADAR swaths that looks anything like the grooves on Ganymede. Whatever has shaped Titan's surface, it is far from obvious whether it has anything to do with the processes that shaped the surfaces of Jupiter's icy satellites (processes that are themselves poorly understood). The icy satellites of the giant planets are fascinating but there is quite a lot of work yet to do to understand just what made them look like they do now.
Apparently for a couple of hours on Monday it looked like there wouldn't be any data -- in fact, for a little while, they heard nothing at all from the spacecraft. Dennis Matson remarked in his opening presentation about Cassini's status today that "there was a lot of consternation" on Monday about not hearing from the spacecraft. I'll bet! It turns out what happened was a cosmic ray hit the solid-state power switch on the ultrastable oscillator, part of the X-band communication system, and shut it off -- right at the worst possible time, just before the planned downlink of the data. I was told that cosmic rays hit power switches with some regularity -- a couple of times a year, I think was the number -- so it's a well-known issue that the mission knows well how to recover from. But the timing of this particular hit was appalling. Fortunately the mission plans for events where they lose their planned downlink; they can quickly swap in a contingency plan to retry the downlink soon enough that they haven't yet wiped and overwritten their data recorders. So in the end, most (but not all) of the T13 data was recovered. They lost a little bit of the end of the SAR swath, and a bunch of planned rings observations that happened after the Titan observations were over. But they did get most of the data back -- and, more importantly, the spacecraft is fine. It was apparently a very nerve-wracking few hours though when they had absolutely no signal from either the high- or low-gain antennas. Imagine suddenly and inexplicably losing a billion-dollar spacecraft! It's happened before, but it's pretty difficult to bear.
More from OPAG in a little bit.