Racing against the Martian winter

With solid findings under its belt and the Martian summer waning, the Phoenix Mars lander perseveres in its study of the soil and sky of the planet’s arctic plain.

After 113 days on Mars, the Phoenix lander is still eating the Red Planet’s icy soil and watching the skies.

MARTIAN DUST This color image shows a three-dimensional view of a tray for sampling Martian dust particles. One particle, which is 1 micrometer wide, sits in the top left cavity (circled) and appears as a red bump. Such dust particles give Mars its characteristic red soil and also color the sky pink. NASA, JPL-Caltech, Univ. of Arizona, Univ. of Neuchatel, Imperial College London

The lander has been working as a robotic geologist on the northern plain of Mars since its May 25 landing. It has found evidence that ice is beneath and in the soil, an important discovery for the mission’s larger purpose to find whether Mars hosts or has hosted environments friendly to life.

Phoenix’s instruments have also identified calcium carbonates in the soil. Carbonates are rocks that, on Earth, form mainly from calcium carbonates that precipitate out of seawater. On Mars, evidence for carbonates has been elusive. The findings, says Michael Hecht of the Jet Propulsion Laboratory in Pasadena, Calif., will soon appear in Science and could mean that liquid water once flowed on Mars.

And Phoenix has confirmed that perchlorate, a chlorine-oxygen compound, is native to the planet; and, that it is snowing ice crystals on Mars.

But the lander has started to shiver, says the mission’s project manager, JPL’s Barry Goldstein.

The Martian summer is waning, so less power is available as less light reaches Phoenix’s solar panels.

“It’s getting quite cold up there in the Martian arctic, so to keep Phoenix warm and working requires more power,” Goldstein says. Researchers are now “scrambling to squeeze every last bit of science from their instruments” before Phoenix flatlines, he says.

The mission was scheduled to end September 30. Recently, though, the team achieved its stated goals for “full mission success” and, because the craft’s power supply remains adequate to conduct experiments, NASA has extended the mission until November 18, Goldstein says.

Phoenix scientists have held few media briefings recently to discuss the mission. But that’s not because the lander’s instruments have been on hiatus, says Ray Arvidson of WashingtonUniversity in St. Louis, coinvestigator for the lander’s robotic arm.

The arm’s scoop has dumped soil samples into all four chemistry beakers of MECA, the Microscopy, Electrochemistry, and Conductivity Analyzer. In the beakers, the samples are mixed with liquid to study the chemistry of the Martian soil. Four of the eight ovens in TEGA, the Thermal and Evolved Gas Analyzer, have also been filled, Arvidson says.

Both instruments confirmed that perchlorate salts are native to Mars. Signals from the soil samples showed there’s too much of the compound for it to have come from the lander’s rockets, says JPL’s Hecht, lead scientist for MECA.

The compound is toxic to humans, but certain microorganisms can “eat perchlorate for breakfast,” Arvidson says. So its existence on Mars doesn’t change the scorecard for life there, Hecht says. It instead changes the rules governing how that potential life would function, he explains.

Using the lander’s LIDAR — a laser-based radar — the team also learned that “it’s snowing on Mars,” Arvidson says. Most crystals vaporized before they reached the ground. But the lander’s camera has taken images of a few ice crystals that landed on some of the instruments.

Discovering that ice exists in the atmosphere and in the soil of Mars is critically important to understanding the nature of water ice in the planet’s past history, comments James Head of Brown University. Head is coinvestigator on the European Space Agency’s Mars Express mission and not involved with Phoenix.

Phoenix’s detection of a layer of water ice a few centimeters below the Martian surface means that “we need to be looking more carefully for water at shallow depths elsewhere,” Head says. Studying the water has major implications for the search for life, he adds.

During past scooping and dumping of samples, however, the icy soil stuck to the robotic arm’s scoop, which meant that for 30 days, TEGA couldn’t analyze the ice samples.

“We still haven’t got enough ice into TEGA to sniff out the isotopes of the water,” Arvidson says.

On September 17 the science team sent commands to the lander to collect another icy sample. After filling the scoop, the robotic arm was to keep the collected soil out of direct sunlight while waiting for dumping commands. Blocking the sun should prevent the ice from slightly vaporizing and should also make it less sticky, Arvidson says.

TEGA’s fifth oven was to be filled September 18, and another one should be done as early as September 20, he adds.

“Our schedule shows the last oven getting filled in early October, if there are no glitches. The only other reason we might not do this is if we run out of power,” says TEGA coinvestigator William Boynton of the University of Arizona in Tucson.

The team plans to continue to analyze soil samples, look at dust grains with MECA’s microscopes and monitor the skies for snow if power lasts through November. Arvidson also hopes to expose more of the subsoil ice layer in order to record how it reacts to the arctic region’s approaching winter.

The team could still do some of these experiments in December, but will have to manage its remaining power and money very carefully, Boynton says.

Clouds of water ice swirl across the Martian sky. In recent days, the lander’s cameras have glimpsed many of these ice hazes. The atmospheric water also forms frost crystals that have been spotted on the lander’s instruments.
NASA, JPL-Caltech, Univ. of Arizona, Texas A&M Univ.

photo of Ashley Yeager

Ashley Yeager is the associate news editor at Science News. She has worked at The Scientist, the Simons Foundation, Duke University and the W.M. Keck Observatory, and was the web producer for Science News from 2013 to 2015. She has a bachelor’s degree in journalism from the University of Tennessee, Knoxville, and a master’s degree in science writing from MIT.

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