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Planetary News: Phoenix (2008)Phoenix Fledges, Science Begins on Unusual Martian SoilBy A.J.S. Rayl
Phoenix has fledged and is flying now into its scientific campaign. The lander has taken its first mission samples, successfully delivered them to two of its highly sophisticated instruments, and is beginning now to determine the composition of the confounding Martian arctic topsoil on which it came to roost May 25. "We have a full oven." Phoenix co-investigator Bill Boynton, lead scientist for the Thermal and Evolved-Gas Analyzer (TEGA) instrument, seemed as relieved as he was happy when he made the announcement at a press conference yesterday. If all goes as planned from here, TEGA will begin its analysis of the Baby Bear sample tomorrow, with preliminary results to come next week. The "definitive scientific numbers," as Boynton put it, may take several weeks. Meanwhile, the optical microscope, part of the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) instrument, is checking out the first sample from the same site today. After several days of a whole lot of shakin' goin' on, Phoenix followed its commands yesterday and conducted yet another TEGA shake, initiating the instrument's vibratory mechanism one more time. The team didn't have much hope this would shake loose enough of the apparently sticky, clumpy particles to make for a sample since it hadn't mustered much for its efforts during shakes on the previous sols, according to Boynton, of the University of Arizona, which is leading the Phoenix mission for NASA. "We were not optimistic," he confirmed. But in the wee hours Wednesday morning, after Phoenix had completed its workday on Mars, the data detailing its efforts arrived in the computers of the TEGA team. "We found out about this perhaps an hour before we have our mid-point meeting and we decided to keep it quiet within the group," Boynton recounted. The mid-point meeting is held in what is effectively the living room or main courtyard of the Science Operations Center at the University of Arizona's Phoenix building, with a representative from each aspect of the mission, engineering and science instruments, commanding a chair. Principal Investigator Peter Smith, oversees the "action" from a director's chair positioned at one end. "At this meeting, the moderator goes around the table and asks each instrument team to talk about the status of their instrument, if the data that came down was reasonable, and if the instrument is working," he explained. "It's usually a 30-second conversation."
When it came to Boynton, however, he offered a few updates on other things, then mentioned the TEGA data had shown the seventh vibration process terminated early. Of course, 'terminated' is a feared word in space circles, because it is usually a sign that something is going really wrong. In this case, however, it was a sign something had gone very right. The instrument is preprogrammed to stop the vibration once it gets the 'oven full' signal. After days of intense not knowing, Boynton worked it for his team. "It terminated," he told his colleagues, "because the oven was full." Then, Boynton punched a button on his laptop and strains of K.C. and the Sunshine Band singing their Bicentennial chart-topper "(Shake, Shake, Shake) Shake Your Booty" filled the air. The team roared, cheering the news and rising from their chairs to give the TEGA king a standing ovation. "We just had a good time for a minute or two," Boynton confessed. The TEGA ovens are tiny -- each holds 20 to 30 Martian microliters of the clumpy arctic topsoil or "a fraction of a teaspoon," as Boynton quantified it. From these small amounts, it will bake and sniff the soil to assess its volatile ingredients, such as water. Not surprisingly, it took mere seconds to fill the tiny oven. "We had been shaking the system for about one second before the dirt started to flow, then it cascaded and filled the oven up almost instantly," said Boynton. "It really just poured in once the dirt started flowing. We're very pleased and ready to get on with things," he added.
Phoenix actually delivered a partial scoopful of the crusty topsoil from the Baby Bear trench to oven #4 on TEGA last Friday, June 6, dumping the soil onto the protective screen, as planned. The objective is to fill the oven cavity, which is no wider than a pencil lead, with fine particles; therefore, protective screens were designed with 1-millimeter-sized holes to prevent larger bits of soil from clogging the narrow ports that lead into the sensitive oven chambers. It turns out the Martian topsoil is so soundly clumpy it doesn't really crumble quite the way science team members thought it would and that presented a problem in getting particles off the clumps small enough to pass through the 1-millimeter wide screen and into the tiny oven. The clumpy soil clods just sat there, solid, on the screen. Although each TEGA chute also features a whirligig mechanism to vibrate the screen and help shake small particles through, the soil just wasn't breaking up enough to get through. After vibration sessions on June 6, 8, and 9, last Friday, Sunday, and Monday, a few particles managed to get through, but thousands are needed for a sample. It's anyone's guess right now as to why the TEGA shake on Wendesday worked and the previous ones did not. Perhaps the cumulative effects of all the vibrating finally did the trick or perhaps a change in the soil's cohesiveness was the reason. One leading theory is that there was ice in that sample. "One of the hypotheses is there was ice in there and it sublimated away, freeing up some of the strength," said Boynton. "It does look like the soil has changed a bit. But, it's just speculation right now." In any case, although TEGA will be looking for ice and water in the samples it receives, the team is not expecting to find ice now in this particular Baby Bear sample. "It's been sitting out in the sunshine now for three or four days now," Boynton pointed out. And since the Sun isn't really setting at the north pole on Mars right now, that's three or four full Martian days, or 24 hours and 39 minutes of exposure.
In the meantime, Phoenix earlier today delivered the first sample of Baby Bear to the optical microscope on the MECA. "Our microscope will allow us to look at the magnetic properties, the distribution and size of the particles, and the different colors to see if they look like different composition," said Smith, also of the University of Arizona. The scientists are anxious to get a good look at this confounding Martian putty. "There's something very unusual about this soil," Smith offered. "Not only is it crusty, it tends to clump into little balls and when you deliver it to a sloped metal surface, like the TEGA, which is sloped at about 45 degrees, it sticks to the side of the surface. This is definitely quite a bit different than all the Mars simulates we were working with in our laboratory doing testing. It looks like just the unusual type of soil we're hoping to find." Beyond being clumpy and crusty and highly cohesive, the material also features a finer quality. "When we first pressed the robotic arm into the soil, you could actually see the imprint of all the details on the back of the scoop, including the screw heads and little metal joints, all imprinted in the soil like you might make an imprint in a fine powder – which has made it confusing for us," Smith admitted. How can something so sticky allow for such perfect imprints? That's one question the Phoenix teams hopes to answer. "We're very interested in the microscopic make-up of the soil," said Smith. "We're interested in learning what sort of chemical and mineral activity has caused the particles to clump and stick together. We want to try and understand its properties." The important lesson learned from the TEGA woes is that dumping is not the way to deliver a sample. This crusty Martian arctic soil is better put into the instruments by sprinkling the sample. So, dumping is out, sprinkling is in.
The sprinkle method -- developed a few months ago by members of Phoenix's arm and microscope teams – requires Phoenix to tilt the scoop with its load of soil on it, then use the scoop's power tool designed for digging into ice -- a motorized rasp -- as a sort of vibrator to gently jostle some material out, instead of turning the scoop over and dumping the contents. "It's a saltshaker mode, if you will, or sprinkler mode," Smith said by way of description. [The rasp is located on the back of the scoop and will be used later in the mission to scrape up samples of subsurface ice.] Virtually all samples will from now on be delivered in this manner, Smith and Boynton confirmed. Today, Phoenix was commanded to sprinkle a spoonful of the strange and sticky Martian soil onto the delivery port of the optical microscope on the MECA instrument. Essentially, this delivery port is a wheel that simply rotates the sample into place for viewing by the microscope. Those images are expected to arrive on Earth today. Throughout this week, Phoenix has also been monitoring the Martian arctic weather and atmosphere, including a collaborative experiment with the Mars Reconnaissance Orbiter (MRO) on Tuesday. As MRO orbited overhead, Phoenix looked up and together they examined the same column of atmosphere simultaneously from above and below. "It allows us to put the Phoenix measurements into global perspective and gives a ground level calibration for the orbiter's measurements," said Leslie Tamppari Phoenix project scientist of NASA's Jet Propulsion Laboratory (JPL). For more:
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