C/2013 A1

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C/2013 A1 (Siding Spring)
NASA-14090-Comet-C2013A1-SidingSpring-Hubble-20140311.jpg
Comet Siding Spring as seen by Hubble on 11 March 2014.
Discovery
Discovered by Siding Spring Observatory
0.5-m Schmidt (E12)[1]
Discovery date 3 January 2013[1]
Orbital characteristics A
Epoch 2014-Oct-30
(JD 2456960.5)[2]
Perihelion 1.39875 AU (q)
Eccentricity 1.00046
Orbital period several million years inbound (Barycentric solution for epoch 1950)[3]
~1 million years outbound
(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] 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.[3] Precovery images by the Catalina Sky Survey from 8 December 2012 were quickly found.[1] On 3 March 2013, Pan-STARRS precovery images from 4 October 2012 were announced that extended the observation arc to 148 days.[4]

Discovery[edit]

The comet was discovered on 3 January 3, 2013 by amateur astronomer Robert McNaught and received the official designation of C/2013 A1 once it was discovered by the Siding Spring Observatory, in Australia. Three images were obtained through the use of CCD cameras mounted on an Uppsala Southern Schmidt Telescope with a parabolic mirror of 0.5 meters in diameter. The comet appeared as an object of magnitude 18.4 to 18.6. Before McNaught, the object had been detected on 8 December 2012 by the telescope of the Catalina Sky Survey observatory of the University of Arizona, although at that time its orbit could not be determined. At the time of discovery, the comet was at 7.2 AU from the Sun.

Precovery images acquired by the Catalina Sky Survey, taken on 8 December 2012 with a Schmidt telescope equipped with a parabolic mirror of 68 cm diameter, were then examined. Subsequently, two other images taken on 4 October 2012 with a 1.8-meter Pan-STARRS telescope with a Ritchey-Chrétien optical configuration, mounted on the summit of Haleakalā, on the island of Maui, in Hawaii, were examined when the comet was estimated as an object ranging from magnitude 19.7 to 20.

Encounter with Mars[edit]

Comet Siding Spring as seen by NEOWISE on 16 January 2014.
Projected position of Comet Siding Spring and its closest approach to Mars on 19 October 2014.
Comet Siding Spring will encounter Mars on 19 October 2014.

Comet Siding Spring will pass extremely close to Mars on 19 October 2014 at 18:30 UTC,[5] so close that the coma may envelop Mars.[6][7] 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.[8] 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).[5] 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).[5]

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
293 0.000252 0.00082 0.0014   18:41
341 0.000443 0.00089 0.0013   18:32
360 0.000546 0.00089 0.0012   18:32
369 0.000607 0.00093 0.0012   18:28
379 0.000595 0.00088 0.0012   18:34
388 0.000690 0.00090 0.0011   18:31
394 0.000775 0.00095 0.0011   18:26
399 0.000801 0.00095 0.0011   18:26
415 0.000853 0.00096 0.0011   18:25
428 0.000868 0.00096 0.0010   18:25
465 0.000875 0.00092 0.0010   18:28
493 0.000867 0.00090 0.00093 18:31

Hypothetical impact[edit]

Hypothetical comet impact at 56 km/s
into sedimentary rock[9]
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)

It is possible that Comet Siding Spring could create a meteor shower on Mars or be a threat to the spacecraft in orbit on its closest approach to Mars.[7] 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).[10]

Estimates for the diameter of the nucleus have varied from 1 to 50 km (0.62 to 31.07 mi).[11][12] C/2013 A1 probably has a nucleus comparable in size to Comet Hyakutake (~4 km).[13] The resulting upper-limit energy of a hypothetical impact with Mars could reach 20 billion megatons.[11][14] The diameter of such a hypothetical impact crater would be roughly ten times the diameter of the comet's nucleus.[11]

The odds of an impact with Mars were 1 in 1250 in March 2013,[15] 1 in 2000 in late March 2013,[12] 1 in 8000 by April 2013,[16] and 1 in 120,000 by 8 April 2013.[17] The 8 April 2013 JPL Small-Body Database 3-sigma solution was the first estimate to show that the minimum approach by Comet Siding Spring would miss Mars.[5]

Observation[edit]

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.[18] 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.[19][20] 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.[20] On the ground are the Curiosity and Opportunity rovers.

References[edit]

  1. ^ a b c d "MPEC 2013-A14 : COMET C/2013 A1 (SIDING SPRING)". IAU Minor Planet Center. 5 January 2013. Archived from the original on 1 March 2013.  (CK13A010)
  2. ^ "MPEC 2013-U73: Observations and Orbits of Comets". IAU Minor Planet Center. 28 October 2013. Archived from the original on 22 February 2014. 
  3. ^ a b c Horizons output. "Barycentric Osculating Orbital Elements for Comet C/2013 A1 (Siding Spring)".  (Solution using the Solar System Barycenter and barycentric coordinates. Select Ephemeris Type:Elements and Center:@0)
  4. ^ "C/2013 A1 (Siding Spring) Orbit". Minor Planet Center. 1 March 2013. 
  5. ^ a b c d "JPL Close-Approach Data: C/2013 A1 (Siding Spring)". 9 February 2014 last obs (arc=493 days w/619 obs). Retrieved 19 February 2013. 
  6. ^ Moorhead, Althea; Wiegert, Paul A.; Cooke, William J. (1 December 2013). "The meteoroid fluence at Mars due to comet C/2013 A1 (Siding Spring)". Icarus 231: 13. Bibcode:2014Icar..231...13M. doi:10.1016/j.icarus.2013.11.028. 
  7. ^ a b Grossman, Lisa (6 December 2013). "Fiercest meteor shower on record to hit Mars via comet". New Scientist. Archived from the original on 12 December 2013. 
  8. ^ Elenin, Leonid (27 February 2013). "New data concerning the close approach of comet C/2013 A1 to Mars". SpaceObs.org blog (ISON-NM). Archived from the original on 4 March 2013. 
  9. ^ Marcus, Robert; Melosh, H. Jay; Collins, Gareth (2010). "Earth Impact Effects Program". Imperial College London / Purdue University. Archived from the original on 10 March 2010.  (solution using 1000kg/m^3, 56km/s, 45 degrees)
  10. ^ Lakdawalla, Emily (5 March 2013). "Will comet Siding Spring make a meteor shower on Mars?". Planetary Society blogs. Archived from the original on 8 March 2013. 
  11. ^ a b c Elenin, Leonid (25 February 2013). "Comet C/2013 A1 (Siding Spring) – a possible collision with Mars". SpaceObs.org blog (ISON-NM). Archived from the original on 2 March 2013. 
  12. ^ a b Phillips, Tony (27 March 2013). "Collision Course? A Comet Heads for Mars". Science News. NASA. Archived from the original on 5 April 2013. 
  13. ^ Černý, Jakub (1 March 2013). "Jak je velké jádro komety C/2013 A1 (Siding Spring)?" [How large is the nucleus of comet C/2013 A1 (Siding Spring)?] (in Czech). Archived from the original on 6 March 2013. 
  14. ^ Bell, Charles (26 February 2013). "Comet C/2013 A1 (Siding Spring)". 
  15. ^ Elenin, Leonid (3 March 2013). "Close approach to Mars. Up-to-date analysis". SpaceObs.org blog (ISON-NM). Archived from the original on 7 March 2013. 
  16. ^ "Mars vs. comet in 2014: Scientists prepare for red planet sky show". CBS News. 1 April 2013. Archived from the original on 2 April 2013. 
  17. ^ DC Agle (12 April 2013). "Comet to Make Close Flyby of Red Planet in October 2014". NASA/JPL. Archived from the original on 8 March 2013. 
  18. ^ Thompson, Bill (28 February 2013). "STEREO-A spacecraft has a ring-side seat of "Siding Spring v's Mars" next year". Sungrazing Comets. Archived from the original on 3 March 2013. 
  19. ^ Moorhead, Althea V.; Wiegert, Paul A.; Cooke, William J. (January 2014). "The meteoroid fluence at Mars due to Comet C/2013 A1 (Siding Spring)". Elsevier B.V: Icarus (online ed.) 231: 13–21. Bibcode:2014Icar..231...13M. doi:10.1016/j.icarus.2013.11.028. 
  20. ^ a b "NASA Preparing for 2014 Comet Watch at Mars". NASA (JPL). 28 January 2014. Archived from the original on 2 February 2014. 

External links[edit]