A UK plan to drive four 'missiles' into the Moon to study its internal structure recently got a boost when tests suggested the missiles' instruments would survive the violent impact.

The probes, part of a proposed UK-NASA collaboration called MoonLITE, could launch as early as 2013. Each would carry a seismometer on board. Together, the network of sensors could use the energy of lunar quakes to map the Moon's interior and help reveal whether the Moon has an iron core, which could shed light on how it formed. A drill and instruments to test for water and other chemicals will also be on board.

Each 'penetrator' may hit the Moon's surface at a speed of more than 1100 kilometres per hour, rapidly coming to a halt as much as 3 metres into lunar dust.

In recent tests, the penetrators were driven by a rocket-powered train into a pile of sand at the speed they would likely hit the Moon. The collision decelerated the load by 10,000 times the strength of gravity – by comparison, ordinary rockets typically do not experience vibrations of more than 100 gs.

The probe's scientific instruments seemed to survive the heavy jolt, says project lead Alan Smith of University College London's Mullard Space Science Laboratory in Surrey, UK. "We're very very pleased," Smith told New Scientist. "We achieved far more than we expected in a very short time."

Light and rugged

To enable the penetrators' scientific instruments to survive the impact, Smith and colleagues embedded the probes' electrical components in a clear block of epoxy and bolted down everything else. Silicon microelectronics were used in some instruments to make the probe lighter and more rugged.

The probes might be able to push metres down into the lunar surface before stopping. But exactly how far is unclear. "The Moon regolith is not like sand. It's more like compressed talcum powder," says Smith. "It does make it harder to penetrate."

If all goes well, the penetrators might be the first to successfully crash into an extraterrestrial object and survive to carry on measurements. The last such attempt to slam instruments into a lunar or planetary surface was in 1999, when NASA's Deep Space 2 mission sent two miniature probes to the surface of Mars.

Organic chemistry

Although the probes seemed to have impacted the surface, the agency was never able to establish communication with them. Other missions have focused on creating impacts to kick up dust or other debris that could be analysed by an orbiting spacecraft.

Communication and power can be two challenges when it comes to developing such impacting probes, says Phil Christensen at Arizona State University in Tempe, US. "But penetrators have always been on the horizon," says Christensen. "There's certainly a lot of things you could do if you poke things into the ground."

On the ground, an impacting probe should be more sensitive to components like organic chemicals than an orbiter studying a plume of soil ejected by a 'dummy' penetrator would be, Christensen says.

Smith says a radioactive source should be able to keep each probe's electronics warm in the cold environment of space. The probes should still be able to communicate by radio through the lunar soil, as it is relatively dry, he adds. Crashing into other bodies in the solar system might require a more creative fix, since moisture can affect the propagation of radio waves.

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