How do you search for chemical evidence of life when you’re 250 million kilometres from your sample?
science
Description
How do you search for chemical evidence of life when you’re 250 million kilometres from your sample?
In the late nineteenth century, speculation was rife that Mars was criss-crossed by geometric canals of
non-natural origin, and that it must therefore be home to an advanced civilisation1
. Since then, the idea
of life on Mars has persisted. With the development of robotic space probes and with the engineering of
increasingly sophisticated scientific instruments, humanity has invested significant time and money over
the last few decades in studying this idea.
In the early 2000s, spectroscopic measurements from Earth-based telescopes suggested that there was
methane in the Martian atmosphere. This is significant, because methane is a relatively reactive
molecule and would only be expected to stay in a planet’s atmosphere for up to a couple of hundred
years. Hence if methane is present, there must be a source that replenishes it as it gradually reacts and
disappears. There are two main ways methane could be produced – geologically (from chemical
reactions occurring in certain types of rocks) or biologically (by certain types of bacteria).
In mid-2012, NASA successfully landed the Mars Science Laboratory (MSL) – otherwise known as
“Curiosity” – in Gale Crater. Curiosity was built to answer two questions: whether methane is present on
Mars, and if so, whether its origin is geological or biological. While the evidence for the presence of
methane is now fairly robust, the second question remains unresolved.
One of the primary instruments carried on the Curiosity rover is SAM (Sample Analysis at Mars). This is
actually a suite of three instruments, one of which is a mass spectrometer. This is used not only to
identify different gases in samples taken from the atmosphere, but also to detect the ratios of different
isotopes in those samples, which provide clues to the origin of the gases.
