The space telescope of the NASA Spitzer found evidence of a collision between two planets around a young star. The star around which it was identified the impact has "only" 12 million years, much less than the 4 and a half billion years of our solar system, and is located in the constellation of the Peacock (Pavo) at a distance of 100 light years from us. The clash involved a planet large like Mars and one like Mercury, both much smaller than the Earth.
The spectrometer of the Spitzer telescope has allowed to identify obsidian and metals sprayed around the star, evidence of an apocalyptic clash occurred at least a thousand years ago. The impact between the two heavenly bodies was particularly violent because they were traveling at a relative speed to each other of 10 km per second, a speed much greater than that normally observed in the impacts between asteroids and planets.
Such an event should have created our moon 4 billion years ago. An asteroid as big as Mars, Theia, clashed against the Earth when its surface was still warm and liquid and was destroyed by the impact. But most of the debris aggregated around the Earth to form the moon that we know. Other impacts of similar power occurred in our solar system, one of them would have hit Venus, causing its retrograde rotation, the reason for which on the planet the sun rises in the west and sets in the east.
Impacts of large celestial bodies are much less common than impacts of asteroids and comets with planets, which occur relatively frequently. On 19 July, the Hubble telescope had identified the impact of an asteroid as big as several football fields on Jupiter. The impact had caused a huge dark cloud of debris into the atmosphere of the giant planet. Such an impact against the Earth would have been much more devastating the Tunguska event, the impact that occurred in 1908, probably with a comet or a fragment of a comet of just 30 meters in diameter.
On Mars a NASA satellite orbiting the planet since 2006 has just sent a fantastic picture of Victoria Crater, about 750 meters large and 70 deep, one of the many created by the impact of a small asteroid on the planet in the remote past.
Francesco Defferrari
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