Moon's 'youngest' crater discovered

Is this the youngest crater on the Moon?

By Dr David Whitehouse BBC News Online science editor

Astronomers have discovered the only known lunar crater to have been formed in recorded history.

In 1953, a flash was seen on the Moon that was taken to be the impact of a small asteroid. But ground-based telescopes were not powerful enough to see any crater.

Now, however, researchers have found a small, fresh, crater in the same position as the flash after searching through more detailed images of the Moon obtained by orbiting spacecraft.

It is believed that new small craters are formed on the Moon every few decades, but this is the first one to have been found.

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Bright, blue and fresh

The 1953 photograph of a flash on the Moon by Leon Stuart, an American amateur astronomer, is the only definite evidence of an asteroid-sized body crashing on to the lunar surface.

Leon Stuart's photograph. The flash is just off-centre

In 1178, Gervase of Canterbury reported seeing a bright flash on the Moon and some researchers believe that a crater called Bruno on the far side was the result, but doubt has been cast on this claim.

Dr Bonnie Buratti, of the US space agency's (Nasa) Jet Propulsion Laboratory in California, and Dr Lane Johnson, of Pomona College, California, looked at Leon Stuart's photograph and estimated that the object that struck the Moon was about 300 metres across and that its impact would have resulted in a crater 1-2 km in size.

They estimate that the energy released in the impact would have been the equivalent of half a Megaton of TNT, or about 35 times more powerful than the Hiroshima bomb.

If it had struck the Earth, such an impact would have caused the destruction of a large metropolitan-sized area.

Soil study

Because such a small crater would not be detectable with Earth-based telescopes, the astronomers examined images taken by spacecraft orbiting the Moon.

Bright, blue and fresh looking

A search of images from the 1994 Clementine mission revealed a 2-km-wide crater with a bright, blue, fresh-appearing blanket of lunar sub-soil splashed around it at the exact location of the 1953 flash.

"Our candidate crater is in the right place," Dr Buratti told BBC News Online. "Its size is consistent with the energy produced by the observed flash; it has the right colour and reflectance, and it's the right shape."

Finding the new crater offers scientists the opportunity to study subsurface unaltered lunar soils before exposure changes them.

The research will be detailed in a forthcoming issue of Icarus, the journal of Solar System studies.