An asteroid about the size of the Titanic caused the dark spot that appeared in Jupiter’s atmosphere on July 19, 2009, according to two papers published recently in the journal Icarus.

Collisions more frequent than we thought

An international team studied the atmospheric temperatures and chemical conditions associated with the impact debris with three infrared telescopes. These observations led to the conclusion that the object was probably an asteroid.

This result was confirmed by NASA’s Hubble Space telescope. The data indicate that the impact debris in 2009 was heavier or denser than debris from comet Shoemaker-Levy 9, in 1994.

Before the collision, scientists had thought that icy comets were the only objects that hit Jupiter, their unstable orbits taking them close enough to be caught by the planet’s gravitational field.

There is now evidence that other objects can hit Jupiter, and that asteroid impacts are more common than we thought.

© Nasa/IRTF/JPL-Caltech/University of Oxford

An explosion on Jupiter

The data showed that the impact had warmed Jupiter’s lower stratosphere by as much as 3 to 4 Kelvin, which is a significant deposition of energy on such a big area. The explosion, which occurred in the deep atmosphere of Jupiter, could only be produced by a rocky body, not by a comet nucleus.

Amateur astronomer notices the spot

The first to notice the dark spot on Jupiter was amateur astronomer Anthony Wesley from Australia. After being informed, Glen Orton and his colleagues at JPL used the Infrared Telescope Facility in Mauna Kea, Hawaii, and other instruments to collect data during the week following the collision.

Scientists are still trying to figure out the frequency of asteroid collisions on Jupiter, but asteroids of this size hit the Earth about once every 100,000 years. Next step of this investigation: use detailed simulations of the impact to refine the size and properties of the object.

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