Comet Siding Spring as seen by NEOWISE on 16 January 2014.
|Discovered by||Siding Spring Observatory
0.5-m Schmidt (E12)
|Discovery date||3 January 2013|
|Orbital characteristics A|
|Perihelion||1.39875 AU (q)|
|Orbital period||several million years inbound (Barycentric solution for epoch 1950)
~1 million years outbound
(Barycentric solution for epoch 2050)
|Next perihelion||25 October 2014|
C/2013 A1 (Siding Spring) is an Oort cloud comet discovered on 3 January 2013 by Robert H. McNaught at Siding Spring Observatory using the 0.5-meter (20 in) Uppsala Southern Schmidt Telescope. At the time of discovery it was 7.2 AU from the Sun and located in the constellation Lepus. Comet C/2013 A1 probably took millions of years to come from the Oort cloud. After leaving the planetary region of the Solar System, the post-perihelion orbital period (epoch 2050) is estimated to be roughly 1 million years. Precovery images by the Catalina Sky Survey from 8 December 2012 were quickly found. On 3 March 2013, Pan-STARRS precovery images from 4 October 2012 were announced that extended the observation arc to 148 days.
Encounter with Mars
Comet Siding Spring will pass extremely close to Mars on 19 October 2014 at 18:30 UTC, so close that the coma may envelop Mars. Initial observations by Leonid Elenin on 27 February 2013, suggested that it might pass 0.000276 AU (41,300 km; 25,700 mi) from the center of Mars. With an observation arc of 493 days, the nominal pass is 0.00090 AU (135,000 km; 84,000 mi) from the center-point of Mars and the uncertainty region shows that it will not come closer than 0.00087 AU (130,000 km; 81,000 mi). For comparison, Mars's outer moon Deimos orbits 0.00016 AU (24,000 km; 15,000 mi) from the planet. Due to the uncertainty region, there is a small possibility that it will pass Mars as far away as 0.00093 AU (139,000 km; 86,000 mi). It will pass Mars at a relative velocity of 56 km/s (35 mi/s).
As seen from Earth, on 19 October 2014 Mars will be in the constellation Ophiuchus, and will be 60 degrees from the Sun. Mars and Comet Siding Spring will also be visible to the STEREO-A spacecraft during the 2014 encounter. The spacecraft MAVEN and Mars Orbiter Mission will arrive at Mars one month before Comet Siding Spring's closest approach. Already in orbit around Mars are Mars Reconnaissance Orbiter, Mars Express, and 2001 Mars Odyssey; all these artificial satellites may be exposed to potentially damaging particles. The level of risk will not be known for months, but NASA is already evaluating "possible precautionary measures" as it prepares for studying the comet. Two key strategies to lessen risk are to get orbiters behind Mars during the minutes of highest risk and to orient orbiters so that their most vulnerable parts are not in the line of impact. On the ground are the Curiosity and Opportunity rovers.
|3 km (1.9 mi)||5.3 million Mt||45 km (28 mi)|
|5 km (3.1 mi)||24.5 million Mt||71 km (44 mi)|
|8 km (5.0 mi)||100 million Mt||108 km (67 mi)|
|15 km (9.3 mi)||660 million Mt||188 km (117 mi)|
|20 km (12 mi)||1.57 billion Mt||242 km (150 mi)|
|50 km (31 mi)||24 billion Mt||544 km (338 mi)|
It is possible that Comet Siding Spring could create a spectacular meteor shower on Mars or be a threat to the spacecraft in orbit on its closest approach to Mars. It will have to be extremely close to Mars for its debris to pose any risk. Millimeter-sized grains will be ejected at about 1 m/s (2 mph), and would take more than a year to travel 100,000 km from Comet Siding Spring.
Estimates for the diameter of the nucleus have varied from 1 to 50 km (0.62 to 31.07 mi). The resulting upper-limit energy of a hypothetical impact could reach 20 billion megatons. C/2013 A1 probably has a nucleus comparable in size to Comet Hyakutake (~4 km). The diameter of such a hypothetical impact crater would be roughly ten times the diameter of the comet's nucleus. Using the older observation arc of 148 days, a Monte Carlo method showed roughly a 1 in 1,250 chance (0.08%) of a Mars impact. As of March 2013, the estimated chance of impact was about 1 in 2000. As of April 2013, the odds of a Mars impact were about 1 in 8000. The 8 April 2013 JPL 3-sigma solution was the first solution to show that the minimum approach by Comet Siding Spring would miss Mars. As of 8 April 2013, the odds of impact were only 1 in 120,000.
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- C/2013 A1 ( Siding Spring ) – Seiichi Yoshida @ aerith.net
- Elements and Ephemeris for C/2013 A1 (Siding Spring) – Minor Planet Center
- Will Comet C/2013 A1 (Siding Spring) Hit Mars? – Ian Musgrave (2 February 2013)
- Could a Comet Hit Mars in 2014? – Ian O'Neill (25 February 2013)
- Update on Comet C/2013 A1 (Siding Spring) and a possible Mars Impact – Ian Musgrave (27 February 2013)
- C/2013 A1 Siding Spring, the first comet of the year – La Cañada Observatory (5 January 2013)
- Will a comet clobber Mars next year? – AstroBob (27 February 2013)
- Close Encounters with the Inner Planets at Sormano Astronomical Observatory
- JPL Small-Body Database Browser nasa.gov