Photo credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University

NASA's Phoenix Mars Lander inserted the four needles of its thermal and conductivity probe into Martian soil during the 98th Martian day, or sol, of the mission and left it in place until Sol 99 (Sept. 4, 2008).

The Surface Stereo Imager on Phoenix took this image on the morning of Sol 99 after the probe was lifted away from the soil. This imaging served as a check of whether soil had stuck to the needles.

The thermal and conductivity probe measures how fast heat and electricity move from one needle to an adjacent one through the soil or air between the needles. Conductivity readings can be indicators about water vapor, water ice and liquid water.

The probe is part of Phoenix's Microscopy, Electrochemistry and Conductivity suite of instruments.

Spiky Probe On Nasa Mars Lander Raises Vapor Quandary

September 04, 2008 -- A fork-like conductivity probe has sensed humidity rising and falling beside NASA's Phoenix Mars Lander, but when stuck into the ground, its measurements so far indicate soil that is thoroughly and perplexingly dry.

"If you have water vapor in the air, every surface exposed to that air will have water molecules adhere to it that are somewhat mobile, even at temperatures well below freezing," said Aaron Zent of NASA Ames Research Center, Moffett Field, Calif., lead scientist for Phoenix's thermal and electroconductivity probe.

In below-freezing permafrost terrains on Earth, that thin layer of unfrozen water molecules on soil particles can grow thick enough to support microbial life. One goal for building the conductivity probe and sending it to Mars has been to see whether the permafrost terrain of the Martian arctic has detectable thin films of unfrozen water on soil particles. By gauging how electricity moves through the soil from one prong to another, the probe can detect films of water barely more than one molecule thick. Read More