A tip of the hat to Ryan over at Martian Chronicles for posting this lovely version of the Santorini panorama, which Opportunity captured just before Mars dipped too close to the Sun in late November of last year. If you click to enlarge you'll get a nice view of some large sand ripples that have wandered over the odd, flat bedrock of Meridiani Planum. Actually what struck me about that rock in this image was that in many places, that bedrock isn't perfectly flat; slabs of rock are tipped up here and there, poking above the otherwise flat surface. I wonder why that happens?
I was very amused to check the Mars Exploration Rover mission status page and find that the most recent update (which only takes us up to sol 1742 or December 17) is titled "Post-Solar Conjunction Hangover." Jim Bell (head of the rovers' camera team and now The Planetary Society's president) had used the term "hangover" to describe Opportunity's condition in a conversation to me last month but I couldn't imagine that the official website would use such a term. Scott Maxwell's blog is taking me back to the early days of the mission, and I'd be willing to bet quite a lot that they'd never have used the term "hangover" in a status update back then. I guess the mission has lasted long enough that the public information officers are taking themselves much less seriously than they used to. (The engineers and scientists never took themselves that seriously.)
Anyway, if you're wondering how a Mars rover can have a hangover, here's what they mean. Opportunity went in to solar conjunction with a lengthy list of things to do, mostly weather measurements and long-duration observations of the composition of a cobble called Santorini with the spectrometers on the end of its robotic arm. This was after it had acquired the images for the panorama above, but before it had a chance to send all that data back to Earth. During the few weeks of conjunction, there was no way to send any more science data back to Earth. When Opportunity had its first communications pass with Odyssey after conjunction was over, it revealed that it had 6,448 different data products in its onboard memory, a worrisome number. It's not that there were too many bits of data, filling up storage -- Opportunity wasn't near that limit. The problem is that having too many different files can trigger a pretty horrible fault on the rovers, the same fault that crippled Spirit for a couple of weeks beginning on sol 18 and which Mark Adler has written about here in the past.
The update said that the potential for the sol 18 fault to happen "becomes a concern when the number of on-board data products is greater than 6,000." 6,448 is way over that limit. Eek. Opportunity had to be nursed carefully through the subsequent couple of days in order to return that valuable conjunction data to Earth, verify its receipt, then delete onboard data products, all without accumulating many more onboard products. It's fine now though. Jim was a little sheepish about causing Opportunity that post-conjunction hangover, but I will say he has a lovely panorama to show for it!