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Plastic casts designed to seek out alien life

June 24, 2005 By Philip Ball This article courtesy of Nature News.

Scientists hope to secure place for biosensor on 2009 Mars mission.

A laboratory weighing no more than a toaster is being developed by British scientists to search for life on other planets.

The system aims to use resilient plastic casts that can selectively recognize different organic molecules to pinpoint traces of organic carbon. The team, including Mark Sims of the University of Leicester, hope to secure a place for their device on board the European Space Agency's ExoMars mission, scheduled for launch in 2009.

This isn't Sims' first experience with Mars. He was previously mission manager for the ill-fated Beagle 2 project. The Beagle 2 craft, which went missing during its approach to the red planet in late December 2003, was designed to look for life by measuring the weights of carbon atoms. A large proportion of lighter atoms is thought to indicate biological processes. Now Sims and his team are working on a different system.

The Specific Molecular Identification of Life Experiment (SMILE) is being designed to search for molecules thought to indicate life (biomarkers). These range from complex hydrocarbons such as those found in crude oil, to amino acids and nucleic acids related to DNA. Should Sims and his team find amino acids, they will also try to work out whether they are left or right 'handed' molecules. Researchers think that an excess of one of these versions would indicate biological processes at work.

Fantastic plastic

The team hopes to find such molecules using an array of patches, each a fraction of a millimetre across, which are selectively sticky for just one biomarker. These patches could be made out of plastic films with molecule-sized cavities in their surface of just the right shape to accommodate a particular biomarker. Cavities such as this can be prepared by casting a polymer around a template biomarker.

Some Earth-bound biosensors work on a similar principle, but use biological patches to trap selective molecules. Sims and colleagues point out that polymers are more robust, and so more likely to survive the harsh conditions of Mars. The polymers also don't pose any risk of contaminating the experiment or the planet with earthly biological material.

The trick now will be refining a device to meet the accuracy and size requirements of a Mars mission. This "requires substantial development work", Sims admits. So they aren't completely ruling out the idea of using biological patches instead.

Not a done deal

The criteria for ExoMars are tough. Researchers hoping to get a place on the craft have to design a device that will look for biomarkers but not exceed 3 kg in mass or measure more than 16x16x20 cm.

Even if the team meets these standards, they will still have politics to contend with. The status of ExoMars is currently up in the air, pending a decision to be made at a conference in December on whether such programmes should continue.

But the researchers intend to press on with SMILE regardless. It may find a home on a NASA mission, they say, or have applications closer to home. "It would have uses ranging from homeland security to forensic science," says Sims. The technology would be particularly valuable for bio-prospecting in extreme environments on Earth, such as deep-sea hot vents, polar ice or deep in the planet's crust, he says.


  1. Sims M. R., et al. Planet. Space Sci., 53. 781 791 (2005).

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