TEGA Update

Bill Boynton
October 28, 2008

• 5 samples analyzed fully
• TA4, Baby Bear: Disturbed surface sample taken soon afterlanding
• TA0, Wicked Witch: sublimation lag from bottom of SnowWhite trench. It had a small amount of ice with it (~1% or less)
• TA5, Rosy Red: A well documented undisturbed surface sample
• TA7, Burn Alive: A deep sample taken beneath Rosy Red to look for differences as a function of depth.
• TA6, repeat of Rosy Red: No quantitative analysis done yet.
• TA1, A “blank” sample: reported on at End of Sol on 10/14. Final quantitative analysis not yet done, but data still look likethe blank is a factor of 10 lower than our signal for low-temperature release of CO₂ (therefore or signal from the otherTAs is not due to terrestrial organics being oxidized by thesample).
• TA3 blank: TA3 oven was closed and used as a second blank to support (and perhaps lower) the blank level found on TA1
• Data just arrived a few hours ago.
• EGA sweep voltage shut down in the middle of the run.
• Don’t know why yet.
• Bad thing is we lost data from 150ºC and above, right where it would have started to be useful.
• Data from TA1 are very likely to be good enough on their own.
• TA2: Never did get a successful sample acquisition.
• All samples show release of CO₂ at low temperature (250ºC to 600ºC)
• This low-temperature CO₂ could have been from FeCO₃, oxidized Mars organics, or oxidized terrestrial organics.
• • Data on TA1 blank suggests we can eliminate terrestrial organics.
• The amount is low, on the order of 0.0x% carbonate (based on CO₂ volume)
• We see a wide range of the amount of CO₂ released at high T
• 700ºC to 1000ºC: almost certainly due to CaCO3.
• Two samples (Baby Bear and Wicked Witch) showed little or no high-T release of CO₂
• • On the order of 0.0x % carbonate
• Rosy Red (1^st) had much more CaCO₃ (on the order of 5%)
• Rosy Red (2^nd) had significant CO₂ release, but not quantified yet.
• Burn Alive has some intermediate amount of CaCO₃, but it is also not yet quantified.
• Not clear why such a big difference (it is almost certainly interesting)
• We have a new way to analyze the released gases now that we understand the nature of their release pattern.
• We collect all of the gases in a certain temperature range and release them for analysis all at once.
• We record the pressure of the gases released as a function of time to know the temperatures of release.
• The total pressure is a good measure of the amount of gas released.
• This approach allows us to have a much higher signal-to-noise ratio for the isotopes of CO2.
• We have been able to demonstrate excellent precision on our measurement of count-rate ratios
• Conversion to isotope ratios depends on getting high precision on our calibration gas, but we expect that to not be a problem.
• Other sources of systematic error must also be evaluated
• For Burn Alive, we got good data on both the low-T and high-T CO3 release.
• For mass 45 we get ± 1.5 ‰ (requirement is 5 ‰)
• For mass 46 we get ± 1.4 ‰ (requirement is 10 ‰)
• Isotopic ratios could help argue for low-T CO2 being from Mars organics rather than carbonates.
• Since the last presentation we have analyzed the calibration gas several times, but have not been able to reduce the data yet.
• Nothing new to discuss here. John Hoffman and Paul Niles will have more results to discuss after we do more data reduction.
• Only thing left to do is GEC run (Gas Enrichment Cell)
• This cell collects gas from the atmosphere and chemically removes the CO₂ and N₂, which is 98% of the gas.
• We increase the pressure of noble gases by a factor of up to 50.
• • This increases our sensitivity by a lot
• There a many, many reasons why knowledge of noble gas abundances is important, but the real question is why measure them with them with Phoenix.
• Viking lander measured some noble gases
• Viking data was good enough that we can have assurances that some gases extracted from SNC meteorites have come from Mars.
• Compositions of gases extracted from meteorites is much better known than what Viking measured or what TEGA could measure.
• For some science applications, meteorite data are not suitable.
  
• Abundances of noble gases in planetary atmospheres are much lower than solar
• Note log axis of 14 decades!
• Mars has had more loss of
  atmosphere than Earth
  
• Compared to solar, atmospheres favor heavy gases.
• Compared to CI chondrites, Ne/Ar/Kr ratios are similar, but Xe is depleted.
• – Hunt for “missing” Xe on Earth
• Depletion of Xe same on Earth and Mars
• – Likely to be not planet specific ^process Swindle (2002) Rev. Min. Geochem.
• Xe isotopes are also fractionated relative to solar.
• Mass 134 and 136 due to fission of ²⁴⁴_Pu.
• Very large enrichment at mass129 is due to decay of ¹²⁹I (t_½ = 16 My)
• Phoenix data would be important for ¹²⁹Xe.
• Viking data very uncertain
  (factor of a few)
  
• Being higher than Earthsuggests loss of atmosphere early
• Mass 136 important for fission Xe

– Why only slightly more fissionXe than on Earth?

-1 (%)

• ³⁶Ar/³⁸Ar on Mars is < 4 vs. 5.3 on Earth.

–

Model to explain it is due to solar-wind-induced sputtering

–

Ratio is not well known

• Viking measurement not very precise (factor of 2)
• Meteorite measurement has large spallation correction