Phoenix Update, Sol 123: Press briefing with carbonates, clays, and snow!
Posted by Emily Lakdawalla
29-09-2008 16:23 CDT
EDIT: I just got a couple of the graphs that they showed during today's briefing, which didn't make it on to the JPL or Arizona websites for some reason. They're included below.
There was a long-awaited press briefing from the Phoenix team this week. They had a lot of ground to cover, with no fewer than six presenters in two different locations, each giving a short summary of something newsy, so a list works best to summarize what they had to say:
- Using their lidar instrument, the meteorological team has detected snow falling from elevations of about 4 kilometers down to 2.5 kilometers, and it probably fell lower before sublimating. They said they'll be watching to see if any snow eventually reaches the ground.
They had a neat graph of this data that hasn't made it to the mission websites yet.Watching snow fall on Mars! Cool.
- Both of the two main analytical instruments, TEGA and MECA, have confirmed the presence of calcium carbonate (a.k.a. calcite) in their samples, relatively abundant at a few percent of the total soil mass. This is important because calcite is usually associated with liquid water.
- The TEGA team thinks they have also detected clay minerals, which isn't much of a surprise. MECA is unable to confirm this yet. This is also no surprise; MECA is designed to detect things that dissolve in water; calcite can dissolve fairly readily under the right conditions, while clays do not.
- The MECA team reported a firmer estimate of the soil pH as 8.3, which they said was very similar to the pH of Earth's oceans. The pH of Earth's oceans is actually buffered in part by feedback cycles among carbonate rocks and carbon dioxide in the atmosphere. If things get more acid, the oceans dissolve calcium carbonate, which, in turn, raises the pH, so the system winds up being pretty stable at that pH.
- The TEGA team has not yet detected organics. Further analysis of the data they already have on the ground could still yield that discovery, and there are still four ovens they haven't filled yet. If it's there, it's "not very much." Still, they are going ahead and performing a TEGA test using the "Organic-free blank" they brought from Earth, which will help them establish TEGA's detection limit.
- Despite several further attempts, they also still haven't gotten an ice sample into TEGA yet. They seem to be giving up on Snow White for now. They may try again, at a different location. They have to hurry to get samples into the remaining four ovens while power levels are still happy.
- Currently, Phoenix is expected to survive through most of November.
- If, by some miracle, it survives the coming Martian winter (during which it will spend hundreds of sols encased in carbon dioxide ice), it is programmed with a "Lazarus mode" to phone home once its batteries are charged enough. Although sunlight will return to the Phoenix site by mid-April, if it does survive, and assuming its solar panels aren't snapped off, it won't be until October that its batteries could charge enough for it to use its radio to attempt contact with Earth.
- There was mention of an interest in turning on MARDI to see if it and its microphone still work, but evidently they haven't taken that step yet.
I've updated the Robotic Arm Camera images page and my sol-by-sol summary for the first time in several weeks (sorry about that hiatus). There have been some neat images lately. Here's my favorites -- a pair of vanity shots, two cameras on the lander taking photos of each other.The mast-mounted camera (SSI) view of the robotic arm camera is even better, because the robotic arm camera flashed its LED lights as the images were being taken. On TEGA, they've opened two more sets of doors, on ovens 2 and 6. Both of them opened in the worst kind of way, with just a tiny gap between the doors. Now only oven 3 is still shut.
It looks like they are trying to deliver material scraped from the organic-free blank to oven 2. (The organic-free blank is a material brought from Earth that they will use to verify any possible organic detection; there is no organic material in the organic-free blank, so whatever signal they want to call "organics" measured from Mars soil had better have a stronger signature than what they see when they test the organic-free blank.) That organic-free blank stuff looks crazily white inside the robotic arm scoop, like freshly fallen snow; here's an image from sol 122 where you can see the dusty stuff inside the scoop. It seems to have another similarity to snow: it blows easily in the Martian wind. Check out this animation (and props to the guys on unmannedspaceflight.com who noticed the material flying away):Here's what TEGA looked like afterward -- what a mess!
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