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Emily LakdawallaDecember 15, 2008

AGU: Some first impressions from today's Phoenix sessions

I have neither the time nor the brainpower to write up all my notes from the Phoenix sessions held this afternoon at the American Geophysical Union meeting, but I thought it was worth hitting some of the high points before I ate dinner.

So far, pretty much everything I have written about Phoenix concerns operational details -- where it dug, what trenches and samples were named, on what sols. So here, for pretty much the first time, are some actual results from some of the instruments. Of most interest to people are results from the Thermal and Evolved Gas Analyzer, or TEGA, and the Wet Chemistry Laboratory, or WCL.

An artist's conception of Phoenix

Phoenix Mission, University of Arizona

An artist's conception of Phoenix
TEGA is the instrument that takes in minute quantities of soil, then slowly heats it and "sniffs" the gases that are driven off; it reaches a maximum temperature of 1000 degrees Celsius. The specific temperatures at which gases arrive in TEGA's mass spectrometer can tell you about what minerals or chemicals they were originally part of in the soil, though the results can be ambiguous, as you'll see below. TEGA is also a calorimeter, which means that it "notices" when the temperature quits rising (or rises faster than you'd expect) as they keep putting in heat, which happens whenever something in the oven is going through a phase transition, like when water goes from ice to gas.

For TEGA results, instrument lead Bill Boynton reported the following:

All in all, there aren't very many definitive results beyond what we knew already. But it's informative to know what their instrument showed, and the range of possibilities that they're considering, and that absence of sulfate is new and very interesting. They expected TONS of sulfate, based upon results from other landed missions. No one offered an explanation for why it should be absent in the Phoenix samples. One other fact that surfaced during questioning of a different talk is that Boynton believes that the data is there for them to measure the isotopic ratios of 12C to 13C and 16O to 18O but that it will be "a month or more before we have definitive numbers." Peter Smith acknowledged that because they never got an ice sample into TEGA they are unlikely to get the ratio of deuterium to regular hydrogen from either the water in the soil or, apparently, from the atmosphere.

OK, so the other instrument of interest is the Wet Chemistry Lab, or WCL. I talked about how WCL works at length in this post; in brief, there were four cells, in which they put some water mixed with some small quantities of other chemical species for calibration purposes, then they put in the Mars sample and stir, then they use sensors to determine the quantity of ions present. After that they drop in slugs of other chemicals to test the response of the solution: first an acid, then three different slugs of barium chloride, which was basically a titration intended to determine the quantity of sulfate present in the soil (see, they expected lots of sulfate).

So here are the main results from WCL, as reported by Sam Kounaves.

IonWt %
So that's the quick-and-dirty summary of the facts, as they stand, from the TEGA and WCL instruments. Smith said that over the next few months they would be hard at work in the laboratory attempting to develop simulated soil compositions that can reproduce the behavior of the Mars soils in these two instruments, and promised results of that at the Lunar and Planetary Science Conference in March.

Today was an insane day, with no break for me from 8 am until now. Tomorrow should be a little bit less insane -- I hope. I still have much to write about from Titan, Enceladus, Phoenix, and even a little bit of Kaguya -- stay tuned.

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
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