A massive scar that appeared in Jupiter's atmosphere last summer was caused by an asteroid 'the size of the Titanic', says NASA.
By examining the signatures of the gases and dark debris produced by the impact shockwaves, the team deduced that the object was more likely a rocky asteroid than an icy comet.
"Both the fact that the impact itself happened at all and the implication that it may well have been an asteroid rather than a comet shows us that the outer solar system is a complex, violent and dynamic place, and that many surprises may be out there waiting for us," said NASA astronomer Glenn Orton. "There is still a lot to sort out in the outer solar system."
Before this collision, scientists had thought that the only objects that hit Jupiter were icy comets whose unstable orbits took them close enough to be sucked in by gravitational attraction. It was believed that Jupiter had already cleared most other objects, such as asteroids, from its sphere of influence.
The July 19, 2009 object likely hit Jupiter between 9 am and 11 am UTC.
As it fell through Jupiter's atmosphere, the object created a channel of super-heated atmospheric gases and debris. An explosion deep below the clouds - probably releasing at least around 200 trillion trillion ergs of energy - then launched debris material back along the channel, above the cloud tops, to splash back down into the atmosphere. Here, it created the aerosol particulates and warm temperatures observed in the infrared.
The blowback blasted ammonia and other gases into the stratosphere.
Scientists computed the set of possible orbits that could have led to such an impact, then searched the catalog of known asteroids and comets. An object named 2005 TS100 - which is probably an asteroid but could be an extinct comet - was one of the closest matches. Although this can't have been the actual impactor, it shows that an asteroid could have hurtled into Jupiter.
"We weren't expecting to find that an asteroid was the likely culprit in this impact, but we've now learned Jupiter is getting hit by a diversity of objects," said NASA scientist Paul Chodas. " Asteroid impacts on Jupiter were thought to be quite rare compared to impacts from the so-called 'Jupiter-family comets,' but now it seems there may be a significant population of asteroids in this category."