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C/2013 A1 (Siding Spring)

Image of comet Siding Spring on 2014 October 19
Copyright © 2014 by Rolando Ligustri

This image was acquired on 2014 October 19, as the comet (lower left) was approaching Mars (the brightest object in the image).

Discovery

Robert H. McNaught (Siding Spring Observatory, New South Wales, Australia) discovered this comet on images acquired during 2013 January 3.54-3.56, using his 51-cm Uppsala Schmidt telescope and a CCD camera. The discovery magnitude was given as 18.4-18.6. Prediscovery images were subsequently found in the archives of Pan-STARRS (Hawaii, USA) and the Catalina Sky Survey (Arizona, USA). The Pan-STARRS observations were made during 2012 October 4.59-4.60 (magnitude 19.7-20.0) and 2012 December 21.37-21.38 (magnitude 19.2). The Catalina Sky Survey observations were made during 2012 December 8.32-8.34 (magnitude 18.5-18.9).

The first observers to independently confirm the comet were Andres Chapman and Nestor D. Diaz (Observatorio Cruz del Sur, San Justo, Buenos Aires, Argentina), when their images from January 4 revealed a magnitude of 18.2-18.4.

Orbit Calculations

The comet moved about one arc minute across the sky during the next 24 hours, indicating it was quite far from the Sun [later calculations reveal the comet was then 7.20 AU from the Sun and 6.54 AU from Earth]. Although, it would normally have taken several weeks to get an accurate orbit, astronomers at the Catalina Sky Survey quickly found the comet on images acquired on 2012 December 8. When combined with over three dozen precise positions of the comet that had been received since the discovery announcement, Gareth V. Williams calculated a parabolic orbit that was published in Minor Planet Electronic Circular 2013-A14 on 2013 January 5. This orbit used 49 positions spanning 2012 December 8 to 2013 January 5, revealing a perihelion date of 2014 October 25.08 and a perihelion distance of 1.39 AU.

Two revised orbits were published in Minor Planet Electronic Circular 2013-A29 on 2013 January 6. Williams found the comet was moving in a hyperbolic orbit, with a perihelion date of between October 24.00-24.34, a perihelion distance of 1.39 AU, and an eccentricity of about 1.001.

One of the most recent orbits was calculated by Syiuchi Nakano and was published in Nakano Note 2757 on 2014 August 25. This used 904 positions from the period spanning 2012 October 4 to 2014 August 22, giving the perihelion date as October 25.30, the perihelion distance as 1.40 AU, and the eccentricity as 1.00044. In addition, Nakano found that the original and future orbits were both elliptical, with orbital periods of 7.5 million years and 879 thousand years.

Mars Encounter

The first apparent mention of a close encounter between this comet and Mars came from Roberto Gorelli on 2013 January 20. Roberto is an amateur astronomer, with a particular interest in meteor showers. He noted that the comet would pass very close to Mars on 2014 October 18-19 and that a meteor shower might be visible. After the comet's orbit had been further improved, Leonid Elenin posted a statement that a collision with Mars was possible. He said the then current orbit calculated for this comet indicated it would pass the red planet at a distance of 68,000 miles (109,200 kilometers) and Mars' moon Deimos at a distance of 3,730 miles (6,000 kilometers). By the beginning of 2014, newer orbits had pushed the closest distance to Mars back to 86,000 miles (138,000 kilometers).

According to a January 28, 2014 press release from NASA's Jet Propulsion Labortory (JPL), the dust being released by the comet could threaten the various spacecraft orbiting Mars. NASA plans to alter the spacecraft orbits so that they are on the opposite side of Mars from the comet when the latter is at its closest approach. Predictions are that the comet's brightness could attain magnitude -8 to -8.5 at Mars. JPL plans to use the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter to potentially acquire images of the comet's nucleus. Although these images will not reveal great details, they could reveal light and dark areas on the nucleus, its shape, and its rotation period. From the surface of Mars, there are plans to use the Curiosity and Opportunity rovers to watch for meteors, as the comet's dust enters Mars' atmosphere. According to Rich Zurek (Mars Exploration Program chief scientist at JPL), they are hoping to study what effect the incoming dust particles have on Mars' atmosphere. Zurek said. "They might heat it and expand it, not unlike the effect of a global dust storm." He is hoping that the infrared sensing instruments on the Mars Reconnaissance Orbiter and Odyssey will be able to monitor this effect.

Observations

Numerous observatories followed this comet through the remainder of 2013. The first visual observation was reported by Alan Hale (New Mexico, USA) on December 25.20. Using his 41-cm reflector, he gave the magnitude as 14.3 and noted a coma 0.4' across. Hale described the comet as, "Small, very faint, condensed...motion verified over the course of an hour." The comet pretty much remained visible on in the Southern Hemisphere during most of 2014. Chris Wyatt (Walcha, New South Wales, Australia) saw the comet using his 25-cm reflector during January 28-30. He gave the magnitude as 14.3-14.4 and noted a slightly condensed coma 0.5-0.6' across. Between February 3 and 24, Wyatt said the comet brightened from magnitude 14.3 to 14.1, while the coma increased in diameter from 0.7' to 1.2'. Michael Mattiazzo (Swan Hill, Victoria, Australia) saw the comet on July 2, using his 20-cm reflector. He gave the magnitude as 11.9 and noted a moderately condensed coma 1' across. On July 29, Wyatt gave the magnitude as 10.5 and noted a moderately condensed coma 4.9' across. He reported the coma appeared "elongated to WSW and an tapered extension of the coma to the NE although faint. Inner coma opaque and bright and wedge shaped portion in direction of coma elongation, with a small central condensation, sometimes appearing stellar but faint." Wyatt saw the coemt again on July 30 and gave the magnitude as 10.4. He said the moderately condensed coma was 4' across, adding that it was still elongated toward the west-southwest. The comet was closest to Earth on September 5 (0.89 AU). David A. J. Seargent (Australia) observed the comet on September 12 and gave the magnitude as 9.7. On October 8, Seargent gave the magnitude as 11.1 and said the moderately condensed coma was 3' across.

Additional Images

Image of comet Siding Spring on 2013 January 20
Copyright © 2013 by Carl Hergenrother

This image was acquired on 2013 January 20 at 6:14:24 UT.


Image of comet Siding Spring on 2013 September 12
Copyright © 2013 by Carl Hergenrother

This image was acquired on 2013 September 12 at 10:44 UT.


Image of comet Siding Spring on 2013 November 5
Copyright © 2013 by A. Maury and J.-F. Soulier

This image was acquired on 2013 November 5 at 3:30:35-5:01:25 UT.


Image of comet Siding Spring on 2014 January 21
Copyright © 2014 by Rolando Ligustri

This image was acquired on 2014 January 21.


Image of comet Siding Spring on 2014 February 2
Copyright © 2014 by SEN/Damian Peach

This image was acquired on 2014 February 2 at 11:27 UT. Damian was using a 51-cm CDK with an FLI ccd camera. He used L, R, G, and B filters, obtaining a 30 minute exposure with the first and 5 minutes with each of the other three.


Image of comet Siding Spring on 2014 September 20
Copyright © 2014 by Martin Mobberley

This image was acquired on 2014 September 20 at 9:55:03-9:57:03 UT.


Image of comet Siding Spring on 2014 September 23
Copyright © 2014 by Martin Mobberley

This image was acquired on 2014 September 23 at 10:05 UT.


Image of comet Siding Spring on 2014 September 26
Copyright © 2014 by Martin Mobberley

This image was acquired on 2014 September 26 at 10:18:54-10:20:54 UT.


Image of comet Siding Spring on 2014 October 8
Copyright © 2014 by Martin Mobberley

This image was acquired on 2014 October 8 at 10:07 UT.


Image of comet Siding Spring on 2014 October 9
Copyright © 2014 by Manos Kardasis

This image was acquired on 2014 October 9 at 9:39:19-9:42:47 UT, while remotely using a 51-cm CDK reflector and a CCD camera at Siding Spring, New South Wales, Australia.


Image of comet Siding Spring on 2014 October 9
Copyright © 2014 by Rolando Ligustri

This image was acquired on 2014 October 9, as the comet was passing the open star cluster M6.


Image of comet Siding Spring on 2014 October 16
Copyright © 2014 by Martin Mobberley

This image was acquired on 2014 October 16 at 10:16:48-10:18:48 UT.


Image of comet Siding Spring on 2014 October 17
Copyright © 2014 by Martin Mobberley

This image was acquired on 2014 October 17 at 9:50:20-9:52:20 UT.


Image of comet Siding Spring on 2014 October 17
Copyright © 2014 by SEN/Damian Peach

This image was acquired on 2014 October 17 at 10:29 UT. Damian was using a 51-cm CDK with an FLI ccd camera. He used L, R, G, and B filters, obtaining a 15 minute exposure with the first and 2 minutes with each of the other three.


Image of comet Siding Spring on 2014 October 18
Copyright © 2014 by Martin Mobberley

This image was acquired on 2014 October 18 at 9:55:24-9:57:24 UT.


Image of comet Siding Spring on 2014 October 19
Copyright © 2014 by Martin Mobberley

This image was acquired on 2014 October 19 at 9:32:00-9:33:00 UT, as the comet (lower left) was approaching Mars (the brightest object in the image).


Image of comet Siding Spring on 2014 October 19
Copyright © 2014 by SEN/Damian Peach

This image was acquired on 2014 October 19 at 11:07 UT, as the comet (lower left) was approaching Mars (the brightest object in the image).

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