Comet Shoemaker–Levy 9 broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of Solar System objects.
The collision provided new information about Jupiter and highlighted its role in reducing space debris in the inner Solar System.
But a much closer event could be in the offing for next year. A newly discovered comet has been found to have an orbit which takes it extraordinarily close to Mars in October 2014 and the possibility of an impact is 1 in 600. The size of the comet is still uncertain but some estimates are of the nucleus being 50 km in diameter. An impact crater on Mars – if an impact occurs – could then be about 500 km in diameter.
C/2013 A1 (Siding Spring) is a comet originating from the Oort cloud and was only discovered in January this year by Robert H. McNaught at Siding Spring Observatory in Australia, using a 0.5-meter Schmidt telescope. By looking at observations made before the comet was identified as a comet on 3rd January, NASA states “Pre-discovery observations located in the archives have extended the observation interval back to Oct. 4, 2012”.
NASA/JPL Near-Earth Object Program Office
March 5, 2013On Oct. 19, 2014, Comet 2013 A1 (Siding Spring) will pass extraordinarily close to Mars, almost certainly within 300,000 km of the planet and possibly much closer. Our current best estimate has it passing about 50,000 km from the surface of Mars. This is about 2.5 times the distance of Mars’ outermost satellite Deimos or less than twice the Earth close approach distance of 2012 DA14 on February 15, 2013. Since the observation span available for orbit determination is still relatively short, the current orbit is quite uncertain and the nominal close approach distance will change as additional observations are included in future orbit estimates. Currently, Mars lies directly within the range of possible paths for the comet and we can’t exclude the possibility that the comet might impact Mars. Our current estimate for the impact probability is less than one in six hundred and we expect that future observations will allow us to completely rule out a Mars impact.
This computer graphic depicts the orbit of comet 2013 A1 (Siding Spring) through the inner solar system. Image credit: NASA/JPL-Caltech
Although the current heliocentric orbit is hyperbolic (i.e., eccentricity greater than one), the orbit is elliptic when expressed in the frame of the solar system’s barycenter. After more than a million year journey, this comet is arriving from our solar system’s distant Oort cloud. It could be complete with the volatile gases that short period comets often lack due to their frequent returns to the sun’s neighborhood.
During the close Mars approach, the comet will likely achieve a total visual magnitude of zero or brighter as seen from Mars-based assets. The attached illustration shows the comet’s approximate, apparent visual magnitude and its solar elongation angle as a function of time as seen from Mars. Because the comet’s apparent magnitude is so uncertain, the brightness curve was cut off at apparent visual magnitude zero. However, the comet may get brighter than magnitude zero as seen from Mars. From Earth, the comet will not likely reach naked eye brightness but it could brighten to visual magnitude 8 as seen from the southern hemisphere in mid-September 2014.
This illustration, prepared by Jon Giorgini, shows the apparent total visual magnitude and solar elongation angle as seen from the center of Mars image NASA
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