The nature and origin of the July 2009 Jovian Impactor.

In 2009 the remains of the comet Shoemaker-Levy 9 were observed impacting the Jovian atmosphere, the first time a body had been directly observed colliding with a planet other than the  Earth, and the first time a comet had ever been seen impacting a planet. At the time this was thought to be an extremely rare event, possibly happening as infrequently as once every 500 years. However in July 2009 a scar similar to that caused by the Shoemaker-Levy 9 impact was observed in the southern hemisphere of Jupiter, suggesting that a similar impact had occurred once again.

In a paper published in the Astrophysics Journal Letters on 12 May 2010 and on the arXiv database at Cornell University Library on 13 May 2010, a team of scientists led by Augustin Sánchez-Lavega of the Universidad del País Vasco in Bilbao discuss the July 2009 Jovian impact, and try to determine the nature and origin of the impactor.

Composite image of Jupiter, with the impact scar as seen at the times indicated at beside the boxes; note this is one scar seen at different times in different positions, not a series of scars as seen with the Shoemaker-Levy impact. Sánchez-Lavega et al. (2010).

The impact scar was first detected at 1.02 am GMT on 20 July 2009, as a dark spot as it rotated into view from the west. The most recent previous image of the same spot was taken at 7.40 am GMT on 19 July 2009, constraining the time of the event that caused it to a 17 hour 22 minute window. Images taken by NASA’s Infrared Telescope Facility at 10.13 am GMT on 20 July 2009 showed a bright spot in the methane and hydrogen absorption bands, reaching high above the surrounding clouds; this was the same pattern observed after the Shoemaker-Levy 9 impacts, suggesting this was another impact of a similar nature.

The July 2009 impact scar seen (a) in visible wavelengths, and (b) in infrared. Sánchez-Lavega et al. (2010)

The scar extended 4800 km east-west and 200 km north-south, though it was tilted at 12˚ to true latitude. This is more elongate than the Shoemaker-Levy 9 scars, which Sánchez-Lavega et al. interpret as a sign that the impacting body had a shallower incidence angle relative to the horizon. A thin debris crescent extended 4800 km northwest of the western edge of the scar; a similar crescent structure was seen after the Shoemaker-Levy 9 impacts, and was interpreted as being the result of Coriolis force on the falling material plus a sliding in the atmosphere that conserves the tangential velocity. 

Working from the size of the impact scar, Sánchez-Lavega et al. calculate the original body to have been between 500 m and 1 km in diameter, and that it struck Jupiter at a speed of between 54.52 and 55.1 kms¯¹. Attempts to model the previous path of the impactor prior to the collision by working backwards from the impact site suggest there was a 47% chance that the body was on its original, Sun orbiting path when it hit Jupiter, and a 53% chance that it had previously been captured by the planet into  a Jovicentric orbit, probably more recently than 1989, as was the case with Shoemaker-Levy 9. Furthermore the previous orbit of the body was equally likely to have been a Main Asteroid Belt body (either a Hilda Group Asteroid or a Quasi-Hilda Comet), or a Jupiter Family Comet. Shoemaker-Levy 9 is thought to have originally been a Quasi-Hilda Comet.

See also…

 Ripples in the rings of Jupiter.

 The nature of the Chicxulub impactor.

 The breakup of Main Belt object P/2013 R3 (Catalina-Pan STARRS).

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Ripples in the rings of Jupiter.

Although fainter and considerably less famous, the planet Jupiter has a system of rings similar to that of Saturn, between the orbits of the small moons Metis and Adriastea. In 1996 the Galileo spacecraft observed a series of ripples within these rings, with material moving as much as 2 km from the plain of the ring. These ripples formed a pair of superimposed and apparently independent spiral patterns. These ripples were again observed by Galileo in 2000, and by the New Horizons spacecraft in 2007.

In a paper published in the journal Science on 6 May 2011, Mark Showalter of the SETI Institute and Matthew Hedman and Joseph Burns of Cornell University proposed that these rings were caused by the interaction of the rings with comet Shoemaker-Levy 9, which broke into a number of pieces following a close encounter with Jupiter in July 1992, and then impacted the planet in a series of collisions in July 1994.

(A) Image taken by the Galileo spacecraft on 9 November 1996, showing the tip of the Jovian ring system. (B) The same image expanded vertically, with two similar frames added to improve signal-to-noise, and a reversed duplicate subtracted. Neutral grey areas are on the plain of the ring, lighter areas raised and darker areas lowered relative to this ring. Hedman et al. (2011).

Hedmen et al. propose that the tilt was caused by particles ejected from Shoemaker-Levy 9 directly impacting the ring, and note that the pattern of ripples observed in 2000 was appeared to have evolved somewhat from that seen in 1996.

The path of particles derived from the comet Shomaker-Levy 9 past Jupiter and its ring system. Particles on the heavy dashed line would pass directly through the ring, and many would impact particles within the ring system, leading to the creation of ripple patterns within the gravitationally bound ring. Hedman et al. (2011).

While this explanation accounts for the observed ring patterns seen in 1996 and 2000, the patterns observed by New Horizons in 2007 require further explanation. The collision between Shomaker-Levy 9 and Jupiter was originally seen as a once in a century event, a similar collision was observed between Jupiter and an unnamed comet on 19 July 2009, suggesting that such events are much more common than was previously thought. Hedman et al. also note that comet 16P/Brooks 2 is thought to have passed very close to Jupiter in 1886, and comet P/Gehrels 3 to have made a close pass of the planet in 1970. Thus they propose that the reinforced ring pattern observed by New Horizons in 2007 could conceivably have been caused by the interaction of the rings with ejecta from an unobserved comet that made a close pass of Jupiter between 2000 and 2007. They further note that similar ripples have been observed in the rings of Saturn by the Cassini space probe, and that these probably have a similar cause.

Ripples on the Jovian ring system observed by New Horizons in 2007. Hedman et al. (2011?).

See also…

 The breakup of Main Belt object P/2013 R3 (Catalina-Pan STARRS).

 The nature and history of 'Quasi-Hilda Object' 2000 YN30.

 Juno Spacecraft to flyby the Earth on Wednesday 9 October 2013.

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