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MECA Finds Perchlorate on Mars, TEGA Still Looking
John Dodge, Editor-in-Chief -- Design News, August 6, 2008
Can MECA and TEGA confirm life or its absence on Mars?
The two sophisticated sets of soil analyzers aboard the Mars Phoenix Lander are trying their hardest and currently, MECA, which stands for Microscopy, Electrochemistry and Conductivity Analyzer, has the lead. MECA is a sensor-based wet chemistry laboratory (nicknamed WCL, pronounced "wickel") that has twice indicated the surprising discovery of perchlorate salts on The Red Planet. So far, TEGA (Thermal and Evolved-Gas Analyzer), which heats soil in an oven and analyzes gases driven off with a mass spectrometer, has come up empty.
"While the WCL tastes the sample, TEGA has the ability to sniff it. You might think we'd be smart to smell something before we tasted it, but frankly I've made the same mistake with sour milk a number of times," joked Michael Hecht, MECA science lead with the Jet Propulsion Laboratory. Clearly elated over MECA's discovery, more of his humor which surfaced in the teleconference can be discovered at the end of this story.
Yesterday, NASA scientists took the unprecedented step of making the perchlorate discovery public earlier than it traditionally would. "We're doing this in the spirit of openness into a better understanding of how science is done. That's the tradeoff of making this research public earlier than planned," said Michael Meyer, chief scientist of the Mars Exploration Program.
The teleconference also attempted to quell the perchlorate rumors that cropped up over the weekend in space blogs and news stories. One CNN report (since updated) asserted Martian soil was toxic and suggested the planet could not support any life.
"Finding perchlorates is neither good nor bad for life, but it does make us reassess how we think about life on Mars," Hecht said. The half dozen scientists on the teleconference yesterday were neutral (one was slightly positive) as to whether the finding enhanced or hurt the prospects of finding life on Mars.
NASA scientists continue to eliminate explanations that the cause of their findings was something other than perchlorate. For instance, perchlorate is used as an oxidant in rocket fuel and could have come from the Lander, but scientists are reasonably confident it did not given the intense focus on making sure the instruments are not contaminated.
Perchlorate, according to NASA, is a charged particle consisting of one chlorine atom and four oxygen atoms. Wikipedia lists nine different types and it can exist in nature or be manufactured. Perchlorate applications are just as diverse: It can be used to treat hyperthyroid conditions or can act as an oxidizer in rocket fuel. In nature, according to NASA, it is found in hyper-arid climates such as the Atacama Desert in Chile which is 50 times drier than Death Valley.
So far, MECA and its 26 ion-detecting sensors have stolen the perchlorate show. TEGA, according to William Boynton, science lead at the University of Arizona which co-built the device with the University of Texas/Dallas, has failed to conclusively find perchlorate in two attempts although the soil samples it used were different than the ones used by MECA.
"We found high temperature release of oxygen (in one) and suggested this could be due to perchlorate or other possibilities that were still open," said Boynton. However, the first test was conducted before they were aware of the MECA's finding. After TEGA was reprogrammed to detect chlorine which could indicate the presence of perchlorate, a second sample was analyzed but no chlorine was found. Chlorine suggests the presence of perchlorate, but does not have to be present for it to be found, Boynton said.
‘We have much work to do and you'll get a final story on this sometime in the future," Boynton said, sounding much like the traditional 'it'll be ready when it's ready' scientist (perhaps not surprisingly, Hecht was in a more talkative mood).
The workings of MECA – "a suite of instruments that include four wet chemistry cells, thermal probe at end of robotic arm and two microscopes" – and the drama discovering the perchlorate are best described in Hecht's own words:
"The basic recipe is simple. We first thaw a container of soaking solution that is mostly water and dispense it in our instrumented beaker and wait awhile for all our sensors to recover from their long frozen trip to Mars. We then add soil and simmer it for several hours stirring frequently.
"Throughout the measurements, we monitor the 26 sensors that line the walls of the beaker. The majority of these sensors are ion-selected electrodes which means they mostly respond to particular type of ion such as sodium, magnesium, potassium, chloride or perchlorate. The 'mostly' is important. We always need to eliminate unusual sources for the signals and that is part of the reason it takes us so long to report on the data.
"The perchlorate was discovered with a multi-use sensor that also has a small sensitivity to other ions such as nitrate, which is part of our calibration solution. Let me explain what I mean by multi-use. If we had a tiny signal from that sensor, it could mean we had a little bit of perchlorate or it could mean we had a lot of nitrates. But a big signal from the same sensor is almost certainly from perchlorate because even if our entire sample were made of nitrates, it would not be enough to produce a response that large.
"When we got our first soil sample Rosy Red back on Sol 30 (a Martian day) and saw a big signal from the perchlorate sensor, we naturally assumed it wasn't working properly. Certainly, there could not be that much perchlorate in the sample. A flurry of lab work in subsequent days convinced us that the sensor was working properly and we were able to reproduce the reading with solutions we intentional spiked with perchlorate.
"Our second WCL cell was analyzed on Sol 41. We saw a similar response from the perchlorate sensor. We were convinced that it was a real indication of perchlorate in the sample because we had now a) reproduced the signal on Mars, b) reproduced it in laboratory and c) eliminated the other likely explanations such as interfering ions.
"But we still had three more tasks to do before we were ready to make a scientific or a public announcement. One was to eliminate some of the more unlikely explanations because it's an unusual finding so in fact we need to entertain unlikely explanations. A second was to increase our understanding of the results by discussing it in detail with colleagues. A third was to verify that the result is consistent with other Phoenix measurements and observations."
Most of those three perchlorate showstoppers have yet to be disproved.
Here's Hecht's other jokes. Hecht, of course, mentioned the stereotype about scientists not getting dates in high school. And given he works in California and is from Massachusetts, he opened his remarks with a denial that the MECA team had any involvement in the Manny Ramirez trade from the Red Sox to the Dodgers.Gallery »
MECA Finds Perchlorate on Mars, TEGA Still Looking
