Space telescope sees planets collide

Scientists have spotted the wreckage from a spectacular collision between two planets deep in space. Two rocky worlds the size of the Moon and Mercury slammed into each other recently in cosmic terms – within a few thousand years.

An artist's impression of the colliding planetsThe impact, at a combined speed of 22,400 mph, destroyed the smaller planet, causing vast amounts of rock to vaporise and flinging huge plumes of hot molten lava into space.

NASA spotted the aftermath of the cosmic car crash, 100 light-years away, using its Spitzer space telescope which picked up the heat from the impact and chunks of rock that have formed from the lava.

Experts say a similar collision about four billion of years ago between a planet the size of Mars with the Earth blasted out the rock and lava that collected together to form the Moon.

Geoff Bryden of NASA’s Jet Propulsion Laboratory in California, said: “This is about the same scale of impact we’re seeing with Spitzer – we don’t know if a moon will form or not, but we know a large rocky body’s surface was red hot, warped and melted.”

Chief investigator Carey M. Lisse, of the Johns Hopkins University in Maryland, said: “This collision had to be huge and incredibly high-speed for rock to have been vaporised and melted.

“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 team observed an old star called HD 172555, in the constellation of Pavo, the Peacock. Spitzer showed unusual chemical fingerprints in the spectrum of the starlight – evidence of silica, or melted glass, from the heat generated by the collision.

Large amounts of silicon monoxide gas, created when the rock was vaporised, were also detected along with rocky rubble flung out from the planets’ wreckage. The scientists will report their discovery in next week’s Astrophysical Journal.

Earth-bound astronomers have previously observed evidence of planets colliding in the Pleiades, of Seven Sisters, a famous star cluster in the constellation of Taurus the bull.

Destructive impacts between worlds were common in the early history of our own solar system, say scientists. Three examples are thought to have stripped Mercury of its outer crust, tipped Uranus on its side and spun Venus backwards.

Fortunately for us, things are a lot quiter now, although there was evidence of an asteroid hitting Jupiter last month and a much smaller object struck the Earth last year. French scientists say that Earth and Mars may one day collide.

Picture: An artist’s impression of the colliding planets (NASA).

• Discover space for yourself and do fun science with a telescope. Here is Skymania’s advice on how to choose a telescope. We also have a guide to the different types of telescope available.

Paul Sutherland

Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.
Paul Sutherland

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Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.

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