In 1953, a doctoral student named Stanley Miller conducted a simple experiment. He created a misture of hydrogen, water and ammonia in a chamber to reproduce the early Earth atmosphere. He sped up “geologic time” by boiling the water and exposing the mix to an electric discharge to simulate lightning. A week later, he was astonished to find that a residue of organic compounds had formed–most notably amino acids, the “building blocks of life”. To date, nobody has been able to create actual life from raw materials, but Miller’s experiment showed that it is possible that life may have evolved from scratch in Earth’s primordial soup.
In December 2002, Jerome Borucki, of the NASA Ames Research Center in California, and his colleagues were conducting a seeminglyl unrelated experiment in which they simulated meteorite impacts on the frozen oceans of Europa by firing aluminium bullets into a block of ice. They were surprised to find that when the bullet impacted, sensors embedded in the ice detected an electric shock. A second, and much larger, electrical discharge was observed a few moments later. No-one had ever put sensors below an impact crater before, Borucki told New Scientist. The team thinks that the current is caused by the movement of protons as the ice cracks.
This could be important because scientists have long speculated that liquid water may lie beneath the shell of ice, many kilometres thick, that covers the surface. Yellow-brown stains seen on the ice by the Galileo probe indicate the possible presence of the molecular building blocks for life. “Europa is a high priority target for exploration because the key ingredients for life seem to be there. But even if you have the ingredients, the question is, is there a spark that creates the first organic molecules?” says planetary scientist Ron Greeley of Arizona State University.
Borucki’s bullet experiments suggest meteorite impacts might have provided that spark. “We do see a handful of very large craters on Europa, and there would have been a lot of energy associated with those,” says Greeley. “These new results are exciting.” Greeley has been appointed by NASA to set the scientific priorities of Jupiter’s Icy Moon Orbiter, the first mission to use nuclear propulsion technologies developed by Project Prometheus, which will visit Europa (possibly even landing to look for organic matter) and two of Jupiter’s other moons, Callisto and Ganymede. The earliest launch date, however, is estimated to be 2011.