Phoenix, a long awaited update

Watching the clouds go by.
Credit: NASA/JPL-Caltech/University Arizona/Texas A&M University

Recently, results from the experimental kit on Phoenix have been slow to be released. Now suddenly there's all this fascinating stuff at once.

The gentle but persistent heat of the analyser ovens (TEGA - Thermal and Evolved Gas Analyzer) and the wet chemistry lab (MECA - Microscopy, Electrochemistry and Conductivity Analyzer) have both recorded firm evidence for calcium carbonate in 'soil' samples from Mars.

From NASA:

The TEGA evidence for calcium carbonate came from a high-temperature release of carbon dioxide from soil samples. The temperature of the release matches a temperature known to decompose calcium carbonate and release carbon dioxide gas, which was identified by the instrument's mass spectrometer.

The MECA evidence came from a buffering effect characteristic of calcium carbonate assessed in wet chemistry analysis of the soil. The measured concentration of calcium was exactly what would be expected for a solution buffered by calcium carbonate.

Calcium carbonate is limestone, or chalk or marble and can even form cave features such as stalactites. It is also an integral part of many marine organisms on Earth. Don't be confused though, there is no evidence for life on Mars, just carbonates which chemically are to be expected given Mars' CO₂ based atmosphere, but it needs water. It's a bit like this:

H₂O + CO₂ --> H₂CO₃

Water plus carbon dioxide gives carbonic acid. Now, remember what happens when you mix a metal, such as calcium, and an acid?

Ca + H₂CO₃ --> Ca₂CO₃ + H₂

You get a salt, calcium carbonate, and hydrogen gas.

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Another part of MECA is the atomic force microscope. They (try to) sieve in some dust from the Martian 'soil' and scan the surface of the particles with incredible precision. Here's an image:


This image's field of view is approximately 23 microns wide. That's 23µm or 23×10⁻⁶m, or 23/1,000,000 metres. That's at the low end of human hair width. It's described as platey material, flat sheets with clearly defined edges.

"We are seeing smooth-surfaced, platy particles with the atomic-force microscope, not inconsistent with the appearance of clay particles," said Michael Hecht, MECA lead scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Clay!

Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks (usually silicate-bearing) by low concentrations of carbonic acid.

TEGA has also found hints of phyllosilicates, These results just drip with water.

Here's the stunner though. It was snowing on Mars.

Martian clouds, like those in the animation above, have been followed by the Meteorological Station (MET) aboard Phoenix. It caries a LIDAR or light detection and ranging instrument. Basically a radar but done with a laser beam.

Watching the clouds go by, with a laser.
Credit: NASA/JPL-Caltech/University Arizona/Canadian Space Agency

Something was dropping out of the clouds and being buffeted by the differing wind speeds as it fell. Ice crystals; we might call it snow.
It can't be frozen carbon dioxide, it's not cold enough for that yet. It is very cold though:

A thin layer of water frost is visible on the ground around NASA's Phoenix Mars Lander in this image taken by the Surface Stereo Imager at 6 a.m. on Sol 79 (August 14, 2008), the 79th Martian day after landing. The frost begins to disappear shortly after 6 a.m. as the sun rises on the Phoenix landing site.
Credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University

As the winter progresses it will get much colder still. Cold to the point where Phoenix will cease to function, and be entombed in ice and solid CO₂. Until the Martian spring that is. As the polar cap again retreats Phoenix will be re-exposed and, if the sunlight charges up it's batteries, it may just manage a last "Still Here". I hope so, this is a great mission.