Constraining the Dust Coma Properties of Comet C/Siding Spring (2013 A1) at Large Heliocentric Distances

Abstract

The close encounter of Comet C/2013 A1 (Siding Spring) with Mars on October 19, 2014 presented an extremely rare opportunity to obtain the first flyby quality data of the nucleus and inner coma of a dynamically new comet. However, the comet's dust tail potentially posed an impact hazard to those spacecraft. To characterize the comet at large heliocentric distances, study its long-term evolution, and provide critical inputs to hazard modeling, we imaged C/Siding Spring with the Hubble Space Telescope when the comet was at 4.58, 3.77, and 3.28 AU from the Sun. The dust production rate, parameterized by the quantity Af$\rho$, was 2500, 2100, and 1700 cm (5000-km radius aperture) for the three epochs, respectively. The color of the dust coma is 5.0$\pm$0.3$\%$/100 nm for the first two epochs, and 9.0$\pm$0.3$\%$/100 nm for the last epoch, and reddens with increasing cometocentric distance out to ~3000 km from the nucleus. The spatial distribution and the temporal evolution of the dust color are most consistent with the existence of icy grains in the coma. Two jet-like dust features appear in the north-northwest and southeast directions projected in the sky plane. Within each epoch of 1-2 hour duration, no temporal variations were observed for either feature, but the PA of the southeastern feature varied between the three epochs by ~30${}^{\circ }$. The dust feature morphology suggests two possible orientations for the rotational pole of the nucleus, (RA, Dec) = (295${}^{\circ }\pm$5${}^{\circ }$, +43${}^{\circ }\pm$2${}^{\circ }$) and (190${}^{\circ }\pm$10${}^{\circ }$, 50${}^{\circ }\pm$5${}^{\circ }$), or their diametrically opposite orientations.

14 pages, 4 figures, 1 table

References in corpus (6)

• Water Ice and Dust in the Innermost Coma of Comet 103P/Hartley 2
• Ensemble Properties of Comets in the Sloan Digital Sky Survey
• An Early Look of Comet C/2013 A1 (Siding Spring): Breathtaker or Nightmare?
• Delivery of dust grains from comet C/2013 A1 (Siding Spring) to Mars
• Trajectory analysis for the nucleus and dust of comet C/2013~A1 (Siding Spring)
• A Study of Dust and Gas at Mars from Comet C/2013 A1 (Siding Spring)

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• The Unusual Apparition of Comet 252P/2000 G1 (LINEAR) and Comparison with Comet P/2016 BA14 (PanSTARRS)