Robot Finds Mars Dry So Far
This color image was acquired by NASA's Phoenix Mars Lander's Surface Stereo Imager on the 20th day of the mission, or Sol 19 (June 13, 2008), after the May 25, 2008, landing. This image shows one trench informally called "Dodo-Goldilocks" after two digs. White material, possibly ice, is located only at the upper portion of the trench. Image
Credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University

Scientists have found no indications so far of water in the first soil sample delivered to NASA's Mars Phoenix Lander, they announced on Monday.

After finally successfully delivering the sample to the Thermal and Evolved-Gas Analyzer (TEGA) on June 11, mission scientists carried out their first two analyses of the sample over the weekend. During the first, the sample was heated to 95 degrees Fahrenheit (35 degrees Celsius), in the hopes of melting out any water ice in the sample. The sample was further heated up to 350 F (175 C) during the second analysis.

"We saw no water coming off the soil whatsoever," said TEGA team leader William Boynton of the University of Arizona.

Boynton says the team wasn't surprised that they found no indication of water ice because the sample sat out in the Martian sun for several days while it was stuck at the entrance to one of TEGA's ovens, which heat up the soil so that the instrument's mass spectrometer can analyze the composition of the vapors the soil gives off.

In the next few days, scientists will further heat the sample up, to a maximum of 1,800 F (1,000 C), to vaporize out minerals that might have chemically-bound water, carbon dioxide or sulfur dioxide.

"We expect there's a high probability that we would find minerals with chemically-bound water, which would release their water at higher temperatures," Boynton said.

Signs of water in the minerals would indicate that rocks on the surface once interacted with liquid water. The twin Mars Exploration Rovers, Spirit and Opportunity, have already found indications of water interacting with surface regolith closer to the Martian equator.

Phoenix has also been expanding its first digging sites, uniting what were once two separate trenches, Dodo and BabyBear. The new, expanded trench has been dubbed "Dodo-Goldilocks."

The mysterious, unidentified white material exposed in the trench is still visible. Mission scientists are still debating whether this bright, white material is exposed subsurface water ice or salt minerals.

"It could be ice; it could be salt. We have to sample it to be able to tell," said Phoenix robotic arm team leader and mission digging czar Peter Arvidson of Washington University in St. Louis.

A small chunk of the material was knocked loose by the robotic arm scoop as it performed one of its backhoe-like maneuvers in the trench. Scientists will be monitoring this chunk and expect to see it change if it actually is ice.

"If it really is ice, we expect it to sublimate, or go into the vapor phase," Arvidson said.

Next, Phoenix will start digging in an area known as "Wonderland," part of the larger "national park" area named "Cheshire Cat" (scientists had set aside some of the digging area for preservation until they had finished their practice digs, so as not to disturb the prime sample-digging soil). Cheshire Cat is "a nice flat top of a polygon," Arvidson said, providing a new type of area for the mission to explore. (These polygons are believed to be formed by the expansion and contraction of water ice under the surface, which creates cracks and uplifts in the soil above it.)

Scientists expected to find water ice about 7.9 inches (20 centimeters) under the surface, but encountered the unidentified white material about 2.3 to 2.7 inches (6 to 7 centimeters) below the surface while digging in one of the trenches bordering a polygon. Arvidson said they hope to see whether they encounter the white material at this depth inside the polygon.

Samples from Wonderland will be delivered to TEGA and the Microscopy, Electrochemistry and Conductivity Analyzer (MECA) instruments in the next week or so, Arvidson said.