Narrowing our search for life on Mars

Written by Cassy Fiford, a recent graduate from UCL and a science communication intern at the European Planetary Science Congress.

What might Martian life look like? Not like little green men, according to Dr Lewis Dartnell, a UK Space Agency research fellow who was talking at the European Planetary Science Congress (EPSC) currently being held at UCL. Dr Dartnell is a former member of the Centre for Planetary Sciences at UCL/Birkbeck.

Even the gloomy Monday morning rain did not dampen the spirits of the many scientists who joined the congress at UCL, each counting down until the 2016 launch of ExoMars, a European space mission with the purpose of finding life on Mars. UCL’s Mullard Space Science Laboratory is playing a leading role in the development of ExoMars, including the design of the main camera, which will land with the second ExoMars probe in 2019.

Contrary to the classic Martian stereotype of little green men, Dr Dartnell and his team have focused on microscopic signs of life. They found that certain minuscule biomarkers, chemical ‘fingerprints’ of life, could be able to withstand the hostile conditions of Mars and may be indicative of life on our neighbouring planet. The survival of these man-made biomarkers in a Mars-like environment means the real thing might have survived on Mars and could be detected by the ExoMars programme.

Dartnell firstly stresses the inhospitable nature of Mars, making us all silently and soggily grateful for the rain. The global magnetic field of Earth protects us like a jacket, sheltering the planet from damaging and powerful radiation. Lacking this atmosphere, Mars is far less fortunate.

“Mars is effectively naked to highly destructive, highly biologically dangerous flight path radiation” says Dartnell. Mars’ ‘nudity’ leaves it vulnerable to huge amounts of radiation from Coronal Mass Ejections, sporadic spurts of energy from the sun, and from galactic cosmic rays from outside of the solar system. When these energetic rays hit atoms they shatter their nuclei, destroying DNA and sending off a cascade of secondary gamma radiation rays, like shrapnel from a bomb.

Yet Dartnell has shown tiny fingerprints of life may persist on Mars despite exposure to these complex and damaging rays. The Raman spectroscope is a scientific instrument that can reveal the chemical makeup of unknown materials, meaning small biomarkers of life can be found from rocks on the surface of Mars. This device is already used by art detectives and personnel at airport security.

Dartnell’s team has used the device to see what remains of a sample of radiation-resistant bacteria after exposing the organism to a harsh Martian weathering experience.

Even after applying 15,000 Gray of radiation to the organism, thousands of times higher than that required to kill a human, traceable signs of life persisted. These biomarkers included chlorophyll and cell protective carotenoids.

The bacteria chosen, Deinococcus radiodurans, is the most radiation resistant organism known to science, and thus rightfully holds the Guinness World Record for the world’s toughest bacterium. Astrobiologists believe that something like this type of hardy creature is the most plausible form of Martian life.

Robotics aboard the ExoMars will take a scoop out of the surface of Mars, allowing the Raman Spectroscope to sample from up to -2m below the surface. It is hoped that less radiation will penetrate to that depth and signs of life will be more common, and in better condition.

However, it is not known how long these fingerprints of life could stick on Mars before being destroyed. Applying increasing radiation eventually causes these biomarkers to be erased, reducing their detectability to the Raman spectroscope.

Dartnell is now looking for other biomarkers which may persist after radiation, such as amino acids and other prebiotic compounds, like chlorophyll. “This work is crucial for understanding what signs to look for to detect remnants of ancient life on Mars that has been exposed to the bombardment of cosmic radiation for very long periods of time,” he says.

By the time ExoMars launches, astrobiologists will have a range of biomarkers in their toolkit to detect past or present life on Mars. To us Earth dwellers in the audience, it seems too long to wait; Dartnell has made us very excited to discover our potential neighbours.