Meanwhile, Back On Mars....

Left: Rover Opportunity's tracks upon leaving Victoria Crater.


What-up with Opportunity? The rover has left Victoria Crater!:

Opportunity has completed one of the most fantastic scientific campaigns of the Mars Exploration Rover mission -- the interior investigation of "Victoria Crater." After spending more than 340 Martian days, known as sols -- almost one Earth year -- inside the crater, Opportunity climbed back out on sol 1634 (Aug. 28, 2008). To do so, Opportunity retraced the wheel tracks the robotic geologist had made while crossing a large sand ripple and entering Victoria on the slopes of an alcove known as "Duck Bay."

And what-up with Phoenix? They saw some dust devils - an expected oddity in the polar summer - but I'm most interested in this business about humidity swings.

These paradoxical humidity measurements are consistent with extremely-cold temperatures, and big temperature swings. The difference between high humidity and very low humidity is very small when temperatures are very low. There is no need to invoke big moisture fluxes:

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.

...Preliminary results from the latest insertion of the probe's four needles into the ground, on Wednesday and Thursday, match results from the three similar insertions in the three months since landing.

"All the measurements we've made so far are consistent with extremely dry soil," Zent said. "There are no indications of thin films of moisture, and this is puzzling."

Three other sets of observations by Phoenix, in addition to the terrestrial permafrost analogy, give reasons for expecting to find thin-film moisture in the soil.

One is the conductivity probe's own measurements of relative humidity when the probe is held up in the air. "The relative humidity transitions from near zero to near 100 percent with every day-night cycle, which suggests there's a lot of moisture moving in and out of the soil," Zent said.