Yesterday I talked a bit about the possibility of life on Mars. It is based on the evidence of recurring pockets of methane on the planet. Possible causes include strange geochemical processes we do not yet understand, or perhaps life. Since the methane is recurring, continuing life seems a likely possibility, although extinct life could have made some methane pockets that periodically show up during thawing or some such process.
Upon nosing around, I found out that there are some pretty solid plans to further investigate this. It turns out that enzymatic processes, such as what occurs in biological systems, tend to use lighter isotopes of hydrogen and carbon in the production of methane. So, variations in isotope mass of the methane gas could signal biological activity. So, how can we determine that?
The usual way is to use a mass spectrometer. This works by using the fact that a charged particle moving in a magnetic field feels a force perpendicular to (and proportional) the velocity. The result is that a charged particle (such as an isotope stripped of an electron or two) will tend to move in a circle, as can be shown in diagrams in the last link. The radius of the circle is equal to the inverse of the magnetic field strength multiplied by the square root of twice the mass times the voltage (which accelerated the particle) divided by the charge (one of these days I’m going to have to find some time to download and configure latex on my Linux box to generate equation images). Basically, the radius of the circle is dependent on the charge to mass ratio. So, it is possible to differentiate between isotopes of different mass. The trick is to get equipment to Mars. It’s a bit large. Another way is to use an optical spectrometer. This measures the frequencies of light absorbed by a gas, and these frequencies are dependent on isotope mass.
At Space.com, they discuss the efforts to include just such a device on the Mars Science Laboratory (MSL) in 2011. It will be a specially made spectrometer 1000 times more sensitive than the spectrometer already included. From the article:
For this reason, he and his colleagues are designing a special kind of optical spectrometer, called a cavity ring-down spectrometer (CRDS), that will be 1,000 times more sensitive than TLS. The CRDS works by illuminating an atmospheric sample with a laser whose frequency can be tuned to resonate with methane molecules of a particular isotopic configuration.
The cavity’s walls are partially mirrored, so light cannot easily escape. Once the laser is turned off, the light keeps bouncing back and forth for several microseconds before it finally peters out — or “rings down.”
The time it takes for ring down is a measure of the amount of the target molecule inside the cavity. In this way, the CRDS can determine the ratios of the different isotopic abundances in Martian methane. Because the light passes through the gas thousands of times before escaping, the CRDS is much better at measuring low concentrations than normal “one-pass” optical spectrometers, Onstott said.
It will take some challenges to get this thing ready for the MSL in just 2 years, but the anticipated results, whatever they are, will be well worth it. Ultimately, what would be ideal is to send some people there to perform extensive testing and exploration. Though, until that time, perhaps a movable lab with a really good AI will suffice, albeit still a challenge as not everything can be anticipated.