Emily LakdawallaAug 05, 2008

What's up in the solar system for the week of August 4

Phoenix: A. J. S. Rayl has an in-depth story up on Thursday's press conference and is preparing an update based on this morning's phone briefing. I'll try to put up a post later today or tomorrow with some other high points from the briefing. But there weren't any surpises, just more depth and background on the detection of perchlorate in the Martian soil by MECA, non-detection by TEGA, what that might mean for its existence on Mars, and context about what perchlorates are and where you find them on Earth. In other news on Phoenix, I think you might find this "Phoenix Diary" entry by MECA scientist Tom Pike on their struggles with the Atomic Force Microscope to be fascinating. An excerpt:

At its core is an exquisitely fine tip which scans over the sample, carefully following the contours to produce a three-dimensional image of the surface. On Earth it is possible to even map out individual atoms on a surface. The tip is at the end of a tiny beam of silicon shaped like a miniature diving board. This silicon diving board has a distinctive twang, way above the acoustic frequencies we can hear, but the AFM can use any slight shift in the tone of the twang to keep the tip scanning just above the surface of the sample. This tips can wear down, so we've sent eight of them, each at the end of their own silicon beam.

This all works very well in the laboratory here on Earth, but on Mars we have a major complication: the temperature swings between -20C in the early afternoon to -80C at night. As the temperature drops, the distinctive tone of the twang rises as the silicon stiffens. We're looking for tiny differences in tone while we scan, but we're being swamped by changes in temperature. It looks as though we might have sent a rather complicated thermometer, rather than a microscope, to Mars....

Moving on: after a relatively quiet summer, we are entering a really exciting season on Cassini. Cassini is now on rev 79, south of the ring plane, and will reach apoapsis and the start of rev 80 on Friday. Next Monday, August 11, is a close flyby of Enceladus, as close as the one that happened on March 12 of this year. Even though the closest approach distance is similar to the March 12 flyby (54 kilometers this time, versus 52 on March 12), Cassini will be flying much deeper into the south polar plume this time than last time. Last time, one of the key instruments, the Cosmic Dust Analyzer, didn't work during the closest part of the flyby due to a software error. I'm sure they've checked and rechecked and triple-checked their code for this one -- hopefully they'll get the results they're looking for.

Cassini's close flybys of Enceladus

Cassini's close flybys of Enceladus
During the prime and extended missions, Cassini will have a total of eight very close flybys of Enceladus. This graph compares their geometry. The Rev 4, 120, 130, and 131 encounters happen when Cassini is on a near-equatorial orbit about Saturn; the other encounters happen with Cassini on more inclined orbits.
ev 3: March 9, 2005, 1,264 km (not pictured)
ev 4: March 9, 2005, 500 km
ev 11: July 14, 2005, 168 km
ev 61: March 12, 2008, 52 km
ev 80: August 11, 2008, 54 km
ev 88: October 9, 2008, 25 km
ev 120: November 2, 2009, 103 km
ev 121: November 21, 2009, 1,607 km (not pictured)
ev 130: April 28, 2010, 103 km
ev. 131: May 18, 2010, 201 km

The MESSENGER team annouced yesterday the delivery of their data to the Planetary Data System, which actually happened a few weeks ago -- and I wish I had time to process and post that data. Maybe later this month. MESSENGER is 62 days (just two months! wow, that's coming up fast) from its next Mercury flyby; it's presently 171 million kilometers from Earth and 100 million kilometers from Mercury.

On the surface of Mars, it is early winter in the southern hemisphere (Ls 109°). Today is sol 1,632 for Spirit and 1,611-2 for Opportunity. The big news on Opportunity this week is that due to some rather scary warning signs of possible impending trouble with the left front wheel, they are aborting their attempts to crawl closer to Cape Verde, and are now working on exiting Victoria Crater. They evidently do not want to get trapped within Victoria by a stuck wheel; they want to get Opportunity back out onto the plains post haste. All this is reported in A. J. S. Rayl's most recent rover report, which concludes with the news that "The next major destination for Opportunity is the cobble field out on the plains, as [Steve] Squyres indicated it would be some months back. 'We're going to drive again across the plains of Meridiani and conduct this cobble campaign, looking at these exposed rocks lying on the surface that tell us about different places on Mars,' [John] Callas elaborated. 'Then we're going to head toward another interesting feature, like another crater. There's a candidate crater [not yet named] about 2 kilometers to the north/northwest from our current location.'" The MARCI team continues to report "uneventful" weather for the landed missions, with just a bit of water ice cloud over Opportunity.

In orbit at Mars, Mars Express did get some great views of Phobos on its recent flyby. A few readers have written in asking me what those grooves are. Here's an earlier blog entry that explains the current thinking. Among this week's Mars Reconnaissance Orbiter HiRISE releases is a new one of Spirit sitting on the edge of Home Plate. (For some reason, whenever I try to type "Home Plate," my fingers type "Home Planet" instead. I wonder why that keeps happening?) My favorite Mars Odyssey THEMIS image of the week is this oen with weird layered terrain in the high northern hemisphere.

At the Moon, Chang'e 1 and Kaguya are currently in orbit. There was a brief news report out of the Chinese Xinhua news agency last week stating that "700 hours" of data from the mission will be released to "domestic authorized users and the European Space Agency" shortly. It further states that as of August 1, Chang'e 1 had orbited the Moon 3,024 times, and that it is about to experience its second eclipse, on August 16.Venus Express is still in orbit at Venus, shifting to a new orbit that'll take it closer to the northern hemisphere. Deep Impact is continuing its EPOCh observations of extrasolar planets. New Horizons is 10.0 AU from Earth and 21.0 AU from Pluto. They're going to need to widen the view of "where is New Horizons now?" beyond the orbit of Saturn, to the orbit of Uranus, pretty soon. The Voyager 1 and 2 website was down just now so I couldn't check their status. Dawn is cruising along -- I have more to post on that soon. Hayabusa, and Stardust are all in cruise mode, talking to Earth from time to time; Genesis is in hibernation.

Finally, I have two calendar items to post. On Friday, August 8, the Dawn mission will be holding a "webinar" featuring Lucy McFadden (an investigator on both the Dawn and Deep Impact missions) speaking about her experiences hunting meteorites in Antarctica. It is at 11:00 MDT (10:00 PDT / 17:00 UTC), and it is free but you need to register in advance here. Then, next week, on August 14-15, there is a conference at APL called the Great Planet Debate. As part of this conference, on August 14 at 16:30 EDT (13:30 PDT / 20:30 UTC), there will be a webcast debate between Neil DeGrasse Tyson and Mark Sykes, moderated by National Public Radio's Ira Flatow, on the nature of planets. Again, you need to go to the conference website to register in advance in order to watch.

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