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Is Martian soil moist?

By Sharon Omahen
University of Georgia

A device borne from the need to test soil moisture around peanut plants is now being used to help test the soil on Mars.

“We designed the device to measure the water content around peanut pods,” said Williams, an agronomist with the University of Georgia College of Agricultural and Environmental Sciences. “At the time, there was no way to measure without disturbing the soil and destroying the pod.”

The year was 1987 and Williams was on sabbatical working with a Washington State University research team led by Gaylon Campbell. The Phoenix Mars Mission landed on the Red Planet May 25. In its tool kit is an advanced version of Williams’ moisture probe.

“We were working on thermal property sensors then to measure heat capacity of soil,” said Campbell, now retired from WSU. “Before, people used a sensor with a single needle having a heater and temperature sensor inside, and measuring the change in temperature over time. We made a dual needle device with a heater in one needle and a temperature sensor in the other.”

Building on the concept

The device worked for Williams’ peanut research. The research team published their findings.

Campbell continued to improve the device. It and other similar models are now developed and sold by Campbell’s company, Decagon, which manufactures measurement devices used by the food and pharmaceutical industries and for agricultural research.

During the American Geophysical Union Meeting in 2004, the sensor device attracted the attention of a scientist working with NASA.

“A scientist from the Jet Propulsion Laboratory (at the California Institute of Technology) stopped by our exhibit and said ‘That’s exactly what I need to send on the Mars lander,’” Campbell said.

And that is where the device is today.

Testing icy soil on Mars

Phoenix’s mission is to study the history of the water now frozen into the Mars permafrost and to check for carbon-containing chemicals that are essential ingredients for life. For the first time, it will also monitor weather at the plant’s polar region from a surface perspective.

NASA’s version of the moisture probe is called the Thermal and Electrical Conductivity Probe. It will test how heat and electricity move through the soil. Ice in the soil can make a big difference in how well the soil conducts heat. The probe is a humidity sensor, too, when held in the air.

Phoenix is a lander, not a rover.

“When it lands it plops down in one spot and a little scoop or shovel on the end of a robot arm will take a sample from the soil on Mars,” Campbell said. “Our sensor is mounted on the scoop and the robot arm pokes it into soil for a measurement.”

So why do we need to know how much moisture is in Mars’ soil?

“They expect to find a lot of water in the polar region of Mars, but it’s believed to be in the form of ice,” he said. “When the robot arm scoops away a thin layer of dust, there should be icy soil below. The sensor will make measurements that confirm that it’s icy soil.”

Scientists on the Mars mission believe the planet used to be covered with water and are determined to find out where the water went.

(Sharon Omahen is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

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