Phoenix Sticks a Fork in Mars
NASA’s Phoenix Mars Lander has touched martian soil with a fork-like probe for the first time and begun using a microscope that examines shapes of tiny particles by touching them.
Phoenix’s robotic arm pushed the fork-like probe’s four spikes into undisturbed soil as a validation test of the insertion procedure. The prongs of this thermal and electrical conductivity probe are about 1.5 centimeters, or half an inch, long. The science team will use the probe tool to assess how easily heat and electricity move through the soil from one spike to another. Such measurements can provide information about frozen or unfrozen water in the soil.
The probe sits on a "knuckle" of the 2.35-meter-long (7.7-foot-long) robotic arm. Held up in the air, it has provided assessments of water vapor in the atmosphere several times since Phoenix’s May 25 landing on far-northern Mars. Researchers anticipate getting the probe’s first soil measurements following a second placement into the ground.
Phoenix also has returned the first image from its atomic force microscope. This Swiss-made microscope builds an image of the surface of a particle by sensing it with a sharp tip at the end of a spring, all microfabricated from a sliver of silicon. The sensor rides up and down following the contour of the surface, providing information about the target’s shape.
"The same day we first touched a target with the thermal and electrical conductivity probe, we first touched another target with a needle about three orders of magnitude smaller — one of the tips of our atomic force microscope," said Michael Hecht of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., lead scientist for the suite of instruments on Phoenix that includes both the conductivity probe and the microscopy station.
The atomic force microscope can provide details of soil-particle shapes as small as about 100 nanometers, less than one-hundredth the width of a human hair. This is about 20 times smaller than what can be resolved with Phoenix’s optical microscope, which has provided much higher-magnification imaging than anything seen on Mars previously.
The first touch of an atomic force microscope tip to a substrate on the microscopy station’s sample-presentation wheel served as a validation test. The substrate will be used to hold soil particles in place for inspection by the microscope. The microscope’s first imaging began Wednesday, July 9, and produced a calibration image of a grooved substrate. "It’s just amazing when you think that the entire area in this image fits on an eyelash. I’m looking forward to exciting things to come," Hecht said.
The spacecraft now has put to use all the capabilities of its Microscopy, Electrochemistry and Conductivity Analyzer, or MECA, suite of instruments. Researchers have begun analyzing data this week from the second sample of soil tested by MECA’s wet chemistry laboratory.
Meanwhile, the Phoenix team is checking for the best method to gather a sample of martian ice to analyze using the lander’s Thermal and Evolved-Gas Analyzer (TEGA), which heats samples and identifies vapors from them. Researchers are using Phoenix’s robotic arm to clear off a patch of hard material uncovered in a shallow trench informally called "Snow White."
Ray Arvidson of Washington University in St. Louis said the hard martian surface that Phoenix has reached proved to be a difficult target, comparing the process to scraping a sidewalk.
"We have three tools on the scoop to help access ice and icy soil," Arvidson said. "We can scoop material with the backhoe using the front titanium blade; we can scrape the surface with the tungsten carbide secondary blade on the bottom of the scoop; and we can use a high-speed rasp that comes out of a slot at the back of the scoop."
Scraping action produced piles of scrapings at the bottom of a trench, but did not get the material into its scoop. The piles of scrapings produced were smaller than previous piles dug by Phoenix, which made it difficult to collect the material into the Robotic Arm scoop.
"It’s like trying to pick up dust with a dustpan, but without a broom," said Richard Volpe, an engineer with JPL on Phoenix’s Robotic Arm team.
Images from the lander’s Robotic Arm Camera showed that the scoop remained empty after two sets of 50 scrapes were collected into two piles in the "Snow White" trench. Now they plan to begin using a motorized rasp on the back of the arm’s scoop to loosen bits of the hard material, which is expected to be rich in frozen water.
"We expected ice and icy soil to be very strong because of the cold temperatures. It certainly looks like this is the case and we are getting ready to use the rasp to generate the fine icy soil and ice particles needed for delivery to TEGA," Arvidson said.