Strengthening case for life on Mars

When it was announced last month that the Mars Odyssey satellite had found water ice beneath the planet`s frozen carbon dioxide south polar ice cap, “I felt excited!” says Dr Lidija Siller, a physicist from the University of Newcastle. “I believe that the data I have explains how this water got trapped underneath the surface”. Dr Siller will be presenting the results of her research – which involves studying photochemical reactions in ice – at the Condensed Matter physics conference on Monday 8 April, part of the Institute of Physics Congress in Brighton.

Photochemical reactions are changes in the chemistry of a substance that occur when light is shone at it. On Mars, both ultraviolet (UV) light from the Sun and low energy electrons can cause photochemical reactions in the carbon dioxide ice caps. The electrons are produced when high energy X-rays from the Sun fall on the ice.

To replicate Martian conditions, Dr Siller creates carbon dioxide ice in an ultra-high vacuum chamber that has been cooled to a very low temperature, then bombards this ice with beams of electrons or photons (tiny particles of light). When the electrons or photons hit the ice, they cause its molecules to split up. Any electrically charged atoms or molecules released by this photochemical process – which would go into the atmosphere on Mars – are then detected via a device known as a mass spectrometer.

In a recent experiment carried out before NASA announced their discovery, Siller looked for a way in which water might get under the Martian ice caps and remain undetected by many of the remote sensing techniques used to analyse planetary surfaces. She put water on top of the carbon dioxide ice, then fired electrons at it. If the water remained on top, its molecules would leave the ice after the electrons hit it.

Although some water molecules were initially detected in the experiment, the rest seemed to disappear, suggesting the electrons were somehow driving the water beneath the surface. “Something happens to this water when I irradiate with electrons. I believe that it is inter-diffusing into the ice,” says Siller. “But more experiments should be done to prove this,” she cautions.

Electrons may not only be likely candidates for trapping the recently detected water on Mars below the surface of the south polar ice cap. If other experiments carried out by Siller are correct, they could also be a possible trigger for the formation of life on the planet.

When she added some hydrogen to carbon dioxide ice and then bombarded it with low energy electrons, oxygen and formaldehyde were released. Oxygen and formaldehyde are both produced by photosynthesis, and, “if photosynthesis is happening, this is the first step for life,” she explains.

Siller hopes to carry out further experiments to determine the precise chemical changes the electrons and photons are causing in the ice.