C/2013 A1

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"Comet Siding Spring" redirects here. For a comet discovered in 2007, see C/2007 Q3.
C/2013 A1 (Siding Spring)
Discovery
Discovered by Siding Spring Observatory
0.5-m Schmidt (E12)[1]
Discovery date 3 January 2013[1]
Orbital characteristics A
Epoch 2013-Feb-05
(JD 2456328.5)[2]
Perihelion 1.400 AU (q)
Eccentricity 1.00038
Orbital period ~400,000 yr
(Barycentric solution for epoch 2050)[3]
Inclination 129.0°
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.[1] Precovery images of the comet by the Catalina Sky Survey from 8 December 2012 were quickly found.[1] Observations by Leonid Elenin on 27 February 2013, suggested the comet might pass 0.000276 AU (41,300 km; 25,700 mi) from the center-point of Mars.[4] On 3 March 2013, Pan-STARRS precovery images from 4 October 2012 were announced that extended the observation arc to 148 days.[5] At the time of discovery the comet 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 400,000 years.[3]

Encounter with Mars[edit]

The comet will pass extremely close to Mars on 19 October 2014 with a very small possibility of an impact event on the planet. With an observation arc of 244 days, the nominal pass is 0.00082 AU (123,000 km; 76,000 mi) from the center-point of Mars and the uncertainty region shows the comet will not come closer than 0.000098 AU (14,700 km; 9,100 mi).[2] For comparison, Mars' outer moon Deimos orbits 23,500 km from the planet. Due to the uncertainty region, there is a small possibility that the comet will pass Mars as far away as 0.0016 AU (240,000 km; 150,000 mi). The comet will pass Mars at a relative velocity of 56 km/s.[2]

JPL Small-Body Database uncertainty region
for close approach to Mars on 19 October 2014
Observation
arc
(in days)		 Minimum
distance
(AU)		 Nominal
distance
(AU)		 Maximum
distance
(AU)		 Nominal
passage
time (UT)
  44 0 0.0059   0.024   10:26
  58 0 0.0025   0.012   15:50
  74 0 0.00070 0.0079 21:00
148 0 0.00035 0.0021 19:28
154 0 0.00074 0.0023 18:50
162 0 0.00079 0.0023 18:45
171 0 0.00080 0.0022 18:44
185 0.00006   0.00076 0.0020 18:51
201 0.000068 0.00080 0.0019 18:45
211 0.000209 0.00079 0.0018 18:45
244 0.000098 0.00082 0.0016 18:41

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 the comet will also be visible to the STEREO-A spacecraft during the 2014 encounter.[6] The spacecraft MAVEN and Mangalyaan will arrive at Mars one month before the comet's closest approach. Already in orbit around Mars are Mars Reconnaissance Orbiter, Mars Express, and 2001 Mars Odyssey. On the ground are the Curiosity and Opportunity rovers.

Comet impact at 56 km/s
into sedimentary rock[7]
Impactor
diameter		 Kinetic energy Crater
diameter
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)

The comet is not expected to create a spectacular meteor shower on Mars or be a threat to the spacecraft in orbit or on the ground. The comet will have to be extremely close to Mars for its debris to pose any real 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 the comet.[8]

Estimates for the diameter of the nucleus have varied from 1 to 50 km (0.62 to 31 mi).[9][10] The resulting upper limit energy of impact could reach 20 billion megatons.[9][11] C/2013 A1 probably has a nucleus comparable in size to Comet Hyakutake (~4 km).[12] The diameter of an impact crater would be roughly ten times the diameter of the comet's nucleus.[9] 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.[13] As of March 2013, the estimated chance of impact was about 1 in 2000.[10] As of April 2013, the odds of a Mars impact were about 1 in 8000.[14] The 8 April 2013 JPL 3-sigma solution was the first solution to show that the minimum approach by the comet would miss Mars.[2] As of 8 April 2013, the odds of impact were only 1 in 120,000.[15]

References[edit]

  1. ^ a b c d "MPEC 2013-A14 : COMET C/2013 A1 (SIDING SPRING)". IAU Minor Planet Center. 2013-01-05. Retrieved 2013-02-01.  (CK13A010)
  2. ^ a b c d "JPL Close-Approach Data: C/2013 A1 (Siding Spring)". 2013-04-07 last obs (arc=185 days w/246 obs). Retrieved 2013-04-09. 
  3. ^ a b Horizons output. "Barycentric Osculating Orbital Elements for Comet C/2013 A1 (Siding Spring)". Retrieved 2013-04-24.  (Solution using the Solar System Barycenter and barycentric coordinates. Select Ephemeris Type:Elements and Center:@0)
  4. ^ Elenin, Leonid (27 February 2013). "New data concerning the close approach of comet C/2013 A1 to Mars". SpaceObs.org blog (ISON-NM). Retrieved 2013-02-27. 
  5. ^ "C/2013 A1 (Siding Spring) Orbit". Minor Planet Center. 2013 03 01. Retrieved 2013-03-03. 
  6. ^ Thompson, Bill (28 February 2013). "STEREO-A spacecraft has a ring-side seat of "Siding Spring v's Mars" next year". Sungrazing Comets. Retrieved 2013-02-28. 
  7. ^ Robert Marcus, H. Jay Melosh, and Gareth Collins (2010). "Earth Impact Effects Program". Imperial College London / Purdue University. Retrieved 2013-02-04.  (solution using 1000kg/m^3, 56km/s, 45 degrees)
  8. ^ Lakdawalla, Emily (2013/03/05). "Will comet Siding Spring make a meteor shower on Mars?". Planetary Society blogs. Retrieved 2013-03-06. 
  9. ^ a b c Elenin, Leonid (25 February 2013). "Comet C/2013 A1 (Siding Spring) – a possible collision with Mars". SpaceObs.org blog (ISON-NM). Retrieved 2013-02-27. 
  10. ^ a b Phillips, Tony (27 March 2013). "Collision Course? A Comet Heads for Mars". Science News. NASA. Retrieved 2013-03-27. 
  11. ^ Bell, Charles (26 February 2013). "Comet C/2013 A1 (Siding Spring)". Retrieved 2013-02-27. 
  12. ^ Černý, Jakub (1 March 2013). "Jak je velké jádro komety C/2013 A1 (Siding Spring)?". Retrieved 2013-03-03. 
  13. ^ Elenin, Leonid (3 March 2013). "Close approach to Mars. Up-to-date analysis". SpaceObs.org blog (ISON-NM). Retrieved 2013-03-03. 
  14. ^ "Mars vs. comet in 2014: Scientists prepare for red planet sky show". CBS News. April 1, 2013. Retrieved 2013-04-06. 
  15. ^ DC Agle (April 12, 2013). "Comet to Make Close Flyby of Red Planet in October 2014". NASA/JPL. Retrieved 2013-04-13. 

External links[edit]

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