Sunday, 27 April 2014

The 3 June 2010 Jovian Impactor.

A small but growing number of observations of bolide impacts on other worlds in the Solar System have been made. The most notable of these are the impact of Comet Shoemaker-Levy 9 into the Jovian atmosphere in 1994 and the July 2009 impact of a similar but unnamed body with the same planet. In addition a number of smaller events have been recorded in recent years, on the Moon, Mars and Jupiter.

In a paper published in the Astrophysical Journal Letters on 9 September 2010 a team of scientists led by Ricardo Hueso of the Universidad del País Vasco report the observation of the impact of a small body into the Jovian atmosphere on 3 June 2010.

The impact was observed by two amateur astronomers, Anthony Wesley of Murrumbateman in New South Wales, Australia, and Christopher Go of Cebu Island in the Philippines. The observation of the impact from two remote sites on Earth confirms that the impact really was in the Jovian atmosphere, rather than being a phenomenon in the atmosphere of Earth. At the time of the impact Wesley was observing Jupiter using a 37 cm telescope with a red filter with an effective wavelength of 650 nm, while Go was using a 28 cm telescope with a blue filter with an effective wavelength of 435 nm. Both were using fast astronomical cameras to make a series of monochrome images, Wesley at 60 frames per second and Go at 55 frames per second.

Bolide in Jupiter’s atmosphere. (a) Colour composite of Jupiter observations by Wesley at 20:31. Each color channel is built by stacking all frames in a 60 s interval. The flash was added to the color image from the red frames with the optical flash. (b) Bolide flash evolution in red wavelengths as obtained by A.W. Each image is a stack of 10 frames obtained sequentially with a total exposition time of 0.17 s (c) Bolide flash evolution in blue wavelengths as obtained by Go Each image is a stack of 5 frames obtained sequentially with a total exposure time of 0.09 s. All times are referenced to the time of the peak of the maximum in the light curve evolution. Hueso et al. (2010).

Follow up observations by other members of the amateur International Outer Planets Watch survey of Jupiter failed to find any sign of the impact, despite the fact that some joined the search within minutes of the impact. Neither were follow up observations by the Hubble Space Telescope and several large observatories on Earth over the following three days successful, implying that the bolide was small in nature. These telescopes looked for residual thermal energy from the impact, traces of ammonia dredged up from the deeper atmosphere by an atmospheric fireball and traces of silicate debris in the upper atmosphere of Jupiter, all phenomena that were observed after the Shoemaker-Levy 9 and July 2009 impacts.

From the images produced by Wesley and Go, Hueso et al. conclude that the object exploded in the Jovian atmosphere above the visible cloud layer, releasing about 2-800 000 000 000  Kilojoules of energy. This is consistent with a rocky body with a mass of 500-2000 tons and a diameter of 8-13 m hitting the Jovian atmosphere at about 60 km per second. Such an object would be predicted to make a spectacular fireball in the Earth’s atmosphere should it hit us, but not to cause any damage at ground level. Such objects are thought to impact the Earth’s atmosphere roughly once every 6-15 years. Estimates of the frequency with which they hit the Jovian atmosphere vary somewhat; those based upon observations of craters on the Galilean Moons predict roughly one such impact a year, whereas estimates based upon the number of known objects in orbits close to that of Jupiter predict between 30 and 100 such impacts per year.

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