火星上的生命(1)

Life on Mars

Life Marker Chip

Astronomers¹ suspect that microscopic² life exists on Mars, or maybe it did. The ExoMars mission funded by the European Space Agency aims to find out. Since the 17th century the possibility of intelligent life on Mars has fascinated us. Scientific speculation³ encouraged the popular belief that Mars was like Earth, complete with continents and oceans, even 'canals' built by sentient⁴ beings to irrigate⁵ deserts. In the early 1920's radio stations were requested by the US government to observe silence so transmissions from Martians could be heard.

Mars missions in the 1970's dismissed any question of life on Mars, David Bowie even wrote a song about this. Subsequently the red planet became a dramatic location for human colonization⁶. These days, comparisons with Earth are made at a molecular⁷ level and the UK-developed Life Marker Chip will be crucial in the ExoMars's hunt for the carbon-based molecules⁹ associated with life.

Test for life

Leicester University's Dr Mark Sims, project leader, describes the Life Marker Chip principle, 'what we use are molecular receptors which are combinations of proteins which act like a lock, the target molecule⁸ which we're trying to find is the key.'

The process is likened to a 'pregnancy¹⁰ test' for life. Dr Sims explains, 'We're putting the receptors down on to a surface, flowing across the organic molecules, getting them to bind¹¹ to the molecular receptors as spots. Using a fluorescing process we then capture an image of those dots and we can send that image back to Earth. By analysing which dots glow we know which molecules are present.'

Signs of life

The potential molecules have been pared down to about 63 and fall in to four classes. Dr Sims describes them, firstly 'The organics which result from meteorites¹² falling on the surface containing carbon molecules. Then the markers left by extinct life, which may have existed three or four million years ago. Thirdly, the molecules associated with existing life. Lastly, there are molecules deposited by spacecraft contamination.'

Earthlings can further benefit from the LMC's sensitivity. Dr Sims emphasizes the LMC's effectiveness in health diagnostics, detecting bacterial¹³ levels in hospitals, or in forensic¹⁴ science for detecting microscopic evidence at crime scenes. Meanwhile, we await transmissions from ExoMars to confirm signs of life on Mars.