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10 February 2014

Seeds of life can sprout in moon’s icy pockets

Is the moon's north pole icy too?
Is the moon’s north pole icy too?

(Image: Clementine Project, BMDO, NRL, LLNL)

Ice pockets on the moon could be cooking up the building blocks of life. Simulations show that cosmic rays coming from outside the galaxy have enough energy to turn simple molecules in lunar ice into more complex organics – carbon-based compounds central to life on Earth.

In 2009, a spacecraft sent crashing into the moon’s south pole kicked up water vapour – probably melted from ice trapped in shadowed craters. That water contained organics, but no one was sure how they got there.

Comets also have organics in their ices, so it is possible that the moon’s carbon-laden water was delivered by impacts. But Sarah Crites at the University of Hawaii at Manoa wondered if the moon could instead be whipping up its organics from scratch.


Slow cooker

Crites and her team modelled the icy chemistry, using radiation data from lunar orbiters, and concluded that cosmic rays striking lunar ice are indeed powerful enough to spark the reactions that would turn basic molecules into organics.

Their simulation suggests that up to 6 per cent of the simpler molecules in the moon’s polar ice, such as carbon dioxide and ammonia, could be converted into organic compounds, such as methane, after being bombarded by cosmic rays for a billion years. That sounds like a long time, but it is only about a quarter of the moon’s age.

The same results apply to Mercury, which is also thought to host water ice at its poles, says Crites. Because cosmic rays are zipping around throughout the solar system, the work suggests that the building blocks of life are appearing in many more places than previously thought. “Organics are not a rare substance in the solar system. They’re getting created everywhere,” says Crites.

That’s not to say that life itself might be forming in frozen reservoirs. The organics created in these simulations would need to become even more complex to be biologically useful, says Michael Callahan at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “You can further react them to make more interesting things,” says Callahan, but the organics made in the current simulation are many steps removed from the base molecules of DNA.

Moon lab

In addition, it is unclear how long organics would survive in lunar ices, as cosmic rays can also break down complex molecules under the right conditions, says Alexander Pavlov, also at Goddard. For instance, it is feared that the harsh radiation conditions on the surface of Mars might have broken down any evidence of past life, if it ever existed. That is partly why the team behind NASA’s Curiosity rover hopes to study areas on Mars that have not been exposed for too long.

Still, Crites’s work hints that we can use lunar ice as a proxy lab for studying chemistry on more distant icy worlds – such as Jupiter’s moons – with greater ease and at a lower cost.

“One of the take-homes is, go back to the moon and look. Dig up samples, see what’s there,” says David Lawrence of Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland.

Journal reference: Icarus, DOI: 10.1016/j.icarus.2013.08.003

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