MECA Finds Perchlorate on Mars, TEGA Still Looking

DN Staff

August 6, 2008

5 Min Read
MECA Finds Perchlorate on Mars, TEGA Still Looking

Can MECAand TEGAconfirm life or its absence on Mars?

The two sophisticated sets of soil analyzers aboard the MarsPhoenix Lander are trying their hardest and currently, MECA,which stands for Microscopy, Electrochemistry and Conductivity Analyzer, hasthe lead. MECAis a sensor-based wet chemistry laboratory (nicknamed WCL, pronounced "wickel") thathas twice indicated the surprising discovery of perchlorate salts on The RedPlanet. So far, TEGA(Thermal and Evolved-Gas Analyzer), which heats soil in an oven and analyzesgases driven off with a massspectrometer, has come up empty.

"While the WCL tastes the sample, TEGAhas the ability to sniff it. You might think we'd be smart to smell somethingbefore we tasted it, but frankly I've made the same mistake with sour milk anumber of times," joked Michael Hecht, MECA science lead with the Jet Propulsion Laboratory. Clearly elatedover MECA's discovery, more of his humor which surfaced in the teleconferencecan be discovered at the end of this story.

Yesterday, NASA scientists took the unprecedented step ofmaking the perchlorate discovery public earlier than it traditionally would. "We'redoing this in the spirit of openness into a better understanding of how scienceis done. That's the tradeoff of making this research public earlier thanplanned," said Michael Meyer, chief scientist of the Mars Exploration Program.

The teleconference also attempted to quell the perchlorate rumorsthat 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 couldnot support any life.

"Finding perchlorates is neither good nor bad for life, butit does make us reassess how we think about life on Mars," Hecht said. The halfdozen scientists on the teleconference yesterday were neutral (one was slightlypositive) as to whether the finding enhanced or hurt the prospects of findinglife on Mars.

NASA scientists continue to eliminate explanations that thecause of their findings was something other than perchlorate. For instance,perchlorate is used as an oxidant in rocket fuel and could have come from theLander, but scientists are reasonably confident it did not given the intense focus onmaking sure the instruments are not contaminated.

Perchlorate, according to NASA, is a chargedparticle consisting of one chlorine atom and four oxygen atoms. Wikipedia lists ninedifferent types and it can exist in nature or be manufactured. Perchlorate applicationsare just as diverse: It can be used to treat hyperthyroid conditions or can actas an oxidizer in rocket fuel. In nature, according to NASA, it is found in hyper-aridclimates such as the Atacama Desertin Chile which is 50 timesdrier than Death Valley.    

So far, MECA and its 26 ion-detecting sensors have stolen theperchlorate show. TEGA, according to William Boynton, science lead at the University of Arizona which co-built the device withthe Universityof Texas/Dallas, has failed to conclusively find perchlorate in twoattempts although the soil samples it used were different than the ones used byMECA.

"We found high temperature release of oxygen (in one) andsuggested this could be due to perchlorate or other possibilities that werestill open," said Boynton. However, the first test was conducted before theywere aware of the MECA's finding. After TEGA was reprogrammed to detectchlorine which could indicate the presence of perchlorate, a second sample wasanalyzed but no chlorine was found. Chlorine suggests the presence ofperchlorate, 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 onthis sometime in the future," Boynton said, sounding much like the traditional 'it'll be ready when it's ready' scientist (perhaps not surprisingly, Hecht wasin a more talkative mood).

The workings of MECA – "a suite of instruments that includefour wet chemistry cells, thermal probe at end of robotic arm and twomicroscopes" – and the drama discovering the perchlorate are best described in Hecht'sown words:

"The basic recipe is simple. We first thaw a container ofsoaking solution that is mostly water and dispense it in our instrumentedbeaker and wait awhile for all our sensors to recover from their long frozentrip to Mars. We then add soil and simmer it for several hours stirringfrequently.

"Throughout the measurements, we monitor the 26 sensors thatline the walls of the beaker. The majority of these sensors are ion-selectedelectrodes which means they mostly respond to particular type of ion such assodium, magnesium, potassium, chloride or perchlorate. The 'mostly' isimportant. We always need to eliminate unusual sources for the signals and thatis part of the reason it takes us so long to report on the data.

"The perchlorate was discovered with a multi-use sensor thatalso has a small sensitivity to other ions such as nitrate, which is part of ourcalibration solution. Let me explain what I mean by multi-use. If we had a tinysignal from that sensor, it could mean we had a little bit of perchlorate or itcould mean we had a lot of nitrates. But a big signal from the same sensor isalmost certainly from perchlorate because even if our entire sample were madeof 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 (aMartian day) and saw a big signal from the perchlorate sensor, we naturallyassumed it wasn't working properly. Certainly, there could not be that much perchloratein the sample. A flurry of lab work in subsequent days convinced us that thesensor was working properly and we were able to reproduce the reading withsolutions we intentional spiked with perchlorate.

"Our second WCL cell was analyzed on Sol 41. We saw asimilar response from the perchlorate sensor. We were convinced that it was a realindication of perchlorate in the sample because we had now a) reproduced thesignal on Mars, b) reproduced it in laboratory and c) eliminated the other likelyexplanations such as interfering ions.

"But we still had three more tasks to do before we wereready to make a scientific or a public announcement. One was to eliminate someof the more unlikely explanations because it's an unusual finding so in factwe need to entertain unlikely explanations. A second was to increase ourunderstanding of the results by discussing it in detail with colleagues. Athird was to verify that the result is consistent with other Phoenix measurements and observations."

Most of those three perchlorate showstoppers have yet to bedisproved.

Here's Hecht's other jokes. Hecht, of course, mentionedthe stereotype about scientists not getting dates in high school. And given heworks in California and is from Massachusetts, he opened his remarks with adenial that the MECA team had any involvement in the Manny Ramirez trade fromthe Red Sox to the Dodgers.

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