09 October 2008
NASA Extends Phoenix Mission as Snow Falls on Martian Plains
Spacecraft soil experiments show past link between minerals and water
Washington — Five months after NASA’s Phoenix spacecraft touched down on the arctic plains of Mars, the instrumented lander has given scientists a new understanding of the Red Planet and its soil, water history, chemistry and climate.
In a region called Vastitas Borealis, at 68 degrees north latitude, 234 degrees east longitude, Phoenix has detected snow falling from Martian clouds, and its soil experiments captured evidence of past interactions between minerals and liquid water — processes that occur on Earth.
“We came to the northern plains of Mars because the Odyssey spacecraft science team told us there was water ice under the plains at 65 to 70 degrees northern latitude. So we wanted to find out about the ice,” Peter Smith, Phoenix’s principal investigator, said during a September 29 briefing.
Smith, of the University of Arizona, leads the mission, with project management at NASA’s Jet Propulsion Laboratory (JPL) and development partnership at Lockheed Martin in Denver. International contributions come from the Canadian Space Agency, the University of Neuchâtel in Switzerland, the universities of Copenhagen and Aarhus in Denmark, the Max Planck Institute in Germany and the Finnish Meteorological Institute.
“In the first couple of months of being on the surface, we were able to determine that the robotic arm could scrape through the surface soils only a few inches deep and reveal an ice layer,” Smith said. “Now our mission is about studying the ice and soil within reach of the robotic arm and to determine if this is a place on Mars that is habitable.”
ON THE GROUND
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 to study rocks and Phoenix was designed to study soil and ice.
While sampling the soil, two Phoenix laboratory instruments — the thermal and evolved gas analyzer and the wet chemistry laboratory of the microscopy, electrochemistry and conductivity analyzer (MECA) — found clues for calcium carbonate, the main composition of chalk, and particles that could be clay. Most carbonates and clays on Earth form only in the presence of liquid water.
“We also know that it’s an alkaline soil with a small sprinkling of salts similar to the salts on Earth, and that there is a component of perchlorate,” Smith said, which on Earth is a nutrient and energy source for microbes.
“Is this a habitable zone on Mars? I think we’re approaching that hypothesis,” Smith said. “We understand, though, that Mars has many surprises for us and we have not finished our investigation.”
Most recently, Phoenix’s arm moved and photographed a rock, then scraped the soil underneath the rock and delivered a few teaspoonfuls of soil onto MECA’s optical and atomic-force microscopes.
Scientists are analyzing the soil, which may contain a high concentration of salts. On Earth, as water evaporates in arctic and arid environments, it leaves behind salt that can be found under or around rocks.
Phoenix scientists have not found liquid water, Smith said, but they know the Martian spin axis — its orientation in relation to the sun — is unstable and that millions of years ago its north pole may have tilted almost directly toward the sun, making the ancient climate much warmer.
MARTIAN WINTER
Phoenix landed on Mars on May 25 with a prime mission of 90 Martian days, each of which, called a “sol,” lasts about 40 minutes longer than an Earth day. (See “Perfect Landing Marks Start of New Mission on Mars.”)
Now, after initially extending the mission from August 26 through September 30, NASA again has extended the mission to allow the spacecraft to function as long as it can into the cold, dark Martian winter.
“As the Martian winter approaches, we lose sunlight,” said JPL Phoenix Project Manager Barry Goldstein. “By the time we get to April [2009], there will be no sun [above the horizon] and that hurts the vehicle in quite a few ways.”
Theoretically, Goldstein said, by October 2009 the solar-powered vehicle could have enough power to come back to life — like its namesake, the mythical firebird that burns and then rises renewed from its own ashes — “although nobody anticipates that the vehicle will survive that harsh winter,” he added.
“There is an end to this mission because of weather,” said Doug McCuistion, director of NASA’s Mars Exploration Program, “but we want to see how far we can get the mission into winter and understand the climatic processes that occur.”
Before darkness drains power from Phoenix, though, “we’re going to try something new,” Smith said. Phoenix has a microphone that the scientists hoped to use during the spacecraft’s descent but that now is turned off.
“We’re going to change the software on the spacecraft and turn on the microphone and try to listen to Mars for the first time,” he said. “This may not succeed — it’s a bit of a gamble — but we think it’s worth it.”
More information about the Phoenix mission is available on the NASA Web site.
