16 June 2008

Two Phoenix Lander Instruments Begin Examining Martian Dirt

Microscopic look at sticky soil may describe Red Planet’s ancient history

This image of soil particles was taken by the optical microscope on Phoenix lander.

By Cheryl Pellerin
Staff Writer

Washington -- For the first time since NASA’s Viking missions in 1976, soil samples are being examined inside instruments on Mars.

Less than a month after the Phoenix lander settled onto the Red Planet’s arctic plains, its robotic arm has delivered soil to two instruments on the lander deck -- a microscope and a bake-and-sniff analyzer called the thermal and evolved-gas analyzer (TEGA). The instruments now are inspecting the samples.

“Our results from these analyses are going to be used to inspire future missions that will come to Mars and hopefully take over where we leave off,” Peter Smith, Phoenix principal investigator at the University of Arizona-Tucson, said during a June 13 briefing, “because we’re bound to raise lots of questions.”

Smith leads the mission, with project management at NASA’s Jet Propulsion Laboratory and development partnership at Lockheed Martin in Denver. International contributions come from the Canadian Space Agency, the University of Neuchatel in Switzerland, the universities of Copenhagen and Aarhus in Denmark, the Max Planck Institute in Germany and the Finnish Meteorological Institute.

ANCIENT HISTORY

Results are not yet back from the TEGA, which has eight separate tiny ovens to bake and sniff soil to assess ingredients like water, but images from Phoenix's optical microscope show nearly 1,000 separate soil particles, down to sizes smaller than one-tenth the diameter of a human hair. Scientists can see at least four distinct minerals.

The sample includes black glassy particles that could have come from ancient Martian volcanoes, and smaller reddish ones that are enriched with iron, which gives the orange material its color.

“It is quite possible,” said Tom Pike of Imperial College London, a Phoenix co-investigator working on the lander's microscopy, electrochemistry and conductivity analyzer, “that what we are looking at is a part of history of Martian soil.”

“If we could turn the clock back,” Pike added, the volcanic lava would pour out onto the surface and over billions of years break down into the glassy particles. Over time, the particles would become enriched with iron, so the particles represent opposite ends of Mars’ historical continuum.

“We know that Mars has then had billions of years to weather the material down and at the same time new material is being revealed,” Pike said. “So you see a continuous process captured at any one point, from relatively unweathered glassy material to this much more weathered, degraded, chemically altered material that is iron enriched and that forms the majority of the particles we’re looking at.”

STICKY SOIL

Stickiness of the soil at the Phoenix site has been a challenge for delivering samples. The first scoop of material stuck to the oven’s screen rather than passing through it, so the scientists used a shaker device on the arm. Finally, after four days, the oven’s indicator showed that it was full. On June 12, the scientists sent the TEGA instructions to begin operating.

This mosaic shows Phoenix’s solar panel and robot arm with soil in scoop.

“We find the soil is very clumpy, it’s very sticky,” Smith said. “It’s an unusual soil not at all like the types of soils we’ve used in our tests, which worked just fine with all the instruments. So we’ve developed another method of collecting samples.”

A key difference between the Phoenix mission and the mission of the other Mars explorers -- the Mars rovers Spirit and Opportunity, which are thousands of kilometers away from the lander -- is that the rovers were designed specifically to study rocks and Phoenix was designed to study soil and ice.

“Looking at rocks,” Smith said, [the rovers] “could understand the ancient environment in which these rocks formed. So the rovers were given mobility in order to get to the rocks and remote sensing equipment, in order to find the rocks.”

The rovers approach rocks, grind off the outer surface layers, put instruments against the rock and measure their composition, take microscopic images of them and do remote sensing with infrared spectrometry.

“The difference with Phoenix is we’re actually able to get soil and ices off the surface -- and this is a more active, younger surface -- and put them into very sophisticated instruments that can modify the materials in a way that we can understand the minerals, the chemicals and the microscropic shapes of sizes of these particles.”

The rovers, he said, “are looking at ancient Mars inside of rocks and we’re looking at modern Mars in the soil and the ices.”

ICE OR SALT?

While digging into the Martian surface to look for ice, the scientists have seen glimpses of a white shiny material that some think is ice and others think could be a layer of salt above the ice.

“Everybody believes there is ice near the surface,” Smith said. Whether that’s it or not is the question.” Other questions are whether the ice layer is thick or thin and whether the robotic arm’s scrapers will be able to get through it.

“Scraping through with our tungsten-carbide scrapers on the scoop is really a high priority for us,” Smith added.

Atmospheric dust near Phoenix has remained about the same day to day so far, said Phoenix co-investigator and atmospheric scientist Nilton Renno of the University of Michigan-Ann Arbor.

"We've seen no major dust clouds at the landing site during the mission so far," he said. "That's not a surprise because we landed when dust activity is at a minimum. But we expect to see big dust storms at the end of the mission. Some of us will be very excited to see some of those dust storms reach the lander."

Studying dust on Mars helps scientists understand atmospheric dust on Earth, which is important because dust is a significant factor in global climate change.

More information about the Mars lander is available on the NASA Web site.