Data collected by NASA's Phoenix Mars Lander before it went silent for good on the Red Planet is providing valuable insight for a new study on the interactions between the Martian dirt and atmosphere.
NASA's Phoenix lander has been sitting idle in the Martian arctic since November 2008, when engineers lost the ability to contact the craft after its solar power supplies were depleted by the Martian winter. Photographs of the Phoenix lander from spacecraft orbiting Mars showed extensive damage to its solar arrays.
But now, Phoenix has a chance to contribute again thanks to a new study that draws on the data the probe gathered before it died.
Vincent Chevrier, a research professor at the Arkansas Center for Space and Planetary Sciences at the University of Arkansas in Fayetteville, has received funding from NASA to study measurements made previously by the now-defunct Phoenix mission. Chevrier hopes to develop a better understanding of how dirt on Mars interacts with the planet's atmosphere, as well as whether these interactions ever produce liquid water.
Phoenix data's new life
Phoenix landed on Mars in May 2008, and conducted a successful mission, outlasting its planned three-month tenure. It carried equipment to take samples of the Martian dirt to search for signs that the environment could be habitable to microbial life.
Chevrier will analyze Phoenix data on Mars dirt's temperature, humidity, electrical conductivity, heat parameters and permittivity, which is the measure of a material's ability to transmit an electric field.
These tens of thousands of measurements, which were collected over the course of about six months, could reveal how the dirt affects the stability of ice and the formation of liquid brine solutions, which contain liquid water.
"Our group has shown that it is thermodynamically possible to have a stable liquid in the soil for a few hours a day under certain conditions," Chevrier said. "The effect of the regolith, or soil, on the water cycle is poorly understood and the Phoenix data provide a unique insight into these processes."
If there is liquid water on Mars, it might cause certain changes in some of the electrical data from the Phoenix lander, Chevrier said. However, those changes could be extremely subtle, or even nonexistent.
"You need a continuous layer of fluid in order to detect changes in these parameters," Chevrier said. "A drop of water won't do it."
Salty Mars dirt
Chevrier's study will also examine the nature and composition of the salts in the Mars dirt at the Phoenix site, including perchlorates, a type of charged compound containing hydrogen, chlorine and oxygen.
The Phoenix mission originally determined the presence of perchlorates on the surface of Mars. These compounds attract water, which means that they may help control humidity in the soil and atmosphere, said Chevrier.
Current meteorological models for Mars are somewhat basic. While they work well for predicting where a Mars explorer should land, they fail to accurately describe the complex atmosphere on the planet, Chevrier said.
The researchers will examine how the soil on Mars interacts with the atmosphere by studying the exchange of water vapor between salts, as well as the speed of absorption where water molecules collect around grains in the soil. Then, they will examine the ice layer under the top layer of soil, looking for signs of sublimation, in which the ice becomes gas and is dispersed through the soil.
Hunting Mars water
After studying the Martian dirt, Chevrier's team will focus on liquid water.
"If the salts can exchange, maybe they will form a brine solution," Chevrier said.
This will require a detailed examination of the data, since Chevrier's previous study showed that liquid water might be stable for a mere two or three hours on a given day.
Chevrier will also reinvestigate the chemical data to detect the possible presence of chlorate, another compound. Currently, Phoenix's measurements do not fit with scientists' understanding of the chemical composition of the Martian soil.
Chevrier and his team of researchers believe the discrepancy may be explained by the presence of chlorates as well as perchlorate. These two molecules appear similar to the instruments on Phoenix, and have approximately the same stability.