August 10, 2009

Evidence of planetary collision discovered

The U.S. space agency says the Spitzer Space Telescope has found evidence of a high-speed collision between two planets orbiting a young star.

Astronomers say that two rocky bodies, one as least as big as our moon and the other at least as big as Mercury, slammed into each other within the last few thousand years or so -- not long ago by cosmic standards, NASA said. The impact destroyed the smaller body, vaporizing huge amounts of rock and flinging massive plumes of hot lava into space.

NASA said Spitzer's infrared detectors were able to identify the signatures of the vaporized rock, along with pieces of refrozen lava, called tektites.

This collision had to be huge and incredibly high-speed for rock to have been vaporized and melted, said Carey Lisse of Johns Hopkins University's Applied Physics Laboratory. This is a really rare and short-lived event, critical in the formation of Earth-like planets and moons. We're lucky to have witnessed one not long after it happened.

Lisse and his colleagues say the cosmic crash is similar to the one that formed our moon more than 4 billion years ago, when a body the size of Mars rammed into Earth.

The discovery by Spitzer, which is managed by NASA's Jet Propulsion Laboratory, is reported in the Aug. 20 issue of the Astrophysical Journal.