Dr. Tom Pike's Blog:

Phoenix diary: Mission to Mars

TUESDAY 1 JULY - CHEMISTRY OR LIFE?

We are investigating whether there is at least the potential there. By contrast, over 30 years ago the two Viking landers each carried a set of four experiments on board designed specifically to detect life on the Red Planet.

One of these experiments mixed a scoopful of the soil with nutrients and looked to see if any of the carbon in these nutrients was given off as gas.

The results were at first astounding - something in the Martian soil did indeed seem to digest the nutrients and expel gas.

But the other three experiments were negative. Was Viking seeing life, or chemical reactions between the nutrients and the soil itself?

On the deck of Phoenix, on one side of the black box that houses the microscope station, are four chemistry experiments waiting to run. This is the Wet Chemistry Laboratory (WCL), essentially four test tubes that will mix the Martian soil with pure water from Earth and see what we can extract.

We will be recreating in these test tubes what we believe would have regularly taken place billions of years ago when Mars was a much warmer and wetter planet. WCL might also give clues to why the soil might have appeared to harbour life in that one Viking experiment.

Inserted into each of the WCL test tubes are a number of sensors - one is an electronic litmus paper which will tell us how acidic or alkaline the soil is. Taken together, the results from all these sensors will give us the best information yet on Mars' surface chemistry.

In particular, if the soil is alkaline this may go a long way to explaining the Viking experiment. Fifteen years ago, one of my Phoenix colleagues, Richard Quinn, worked out that just such a soil would explain the Viking results.

He is now in the Phoenix science operations center (SOC), anxious to get soil into the first of these test tubes.

It has taken a while - nearly 30 days since Phoenix landed - to make sure we are ready to go with WCL.

It requires a complex sequence of releasing water from a tank, bringing soil into the test tube, stirring the mixture up to make sure we release all the soluble chemicals, and, finally, taking a slew of measurements from the resulting brew.

We have only one shot at it, and we want to make sure the spacecraft follows these instructions to the letter.

The first sample for WCL comes from the top few centimetres of the Martian soil. The optical microscope has already indicated this very top surface uniformly coats Mars. Near the Martian equator, Viking probably looked at a very similar scoop of material to what Phoenix has dug up from the "arctic" plains.

The data streams down, filing up our computer screens with scans from all the sensors. There's a quiet smile on Richard's face as he concentrates on just one of these lines - the soil is just about as alkaline as he expected.

It looks like one of the biggest mysteries from previous missions to Mars has been cracked by Phoenix. It was the chemical reactions of nutrients with the chemistry of the soil, not life, that Viking saw back in 1976.

No one should be surprised. Now can we finally put Gil Levin to rest?