D. Bodewits¹, T. L. Farnham¹, M. F. A’Hearn¹, L. M. Feaga¹, A. McKay^2,3, D. G. Schleicher⁴ and J. M. Sunshine¹

¹Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
²Astronomy Department, New Mexico State University, Las Cruces, NM 88003, USA
³University of Texas Austin/McDonald Observatory, 1 University Station, Austin, TX 78712, USA
⁴Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA

We used the Ultraviolet-Optical Telescope on board Swift to observe the dynamically young comet C/2009 P1 (Garradd) from a heliocentric distance of 3.5 AU pre-perihelion until 4.0 AU outbound. At 3.5 AU pre-perihelion, comet Garradd had one of the highest dust-to-gas ratios ever observed, matched only by comet Hale-Bopp. The evolving morphology of the dust in its coma suggests an outburst that ended around 2.2 AU pre-perihelion. Comparing slit-based measurements and observations acquired with larger fields of view indicated that between 3 AU and 2 AU pre-perihelion a significant extended source started producing water in the coma. We demonstrate that this source, which could be due to icy grains, disappeared quickly around perihelion. Water production by the nucleus may be attributed to a constantly active source of at least 75 km², estimated to be >20% of the surface. Based on our measurements, the comet lost 4 × 10¹¹ kg of ice and dust during this apparition, corresponding to at most a few meters of its surface. Even though this was likely not the comet’s first passage through the inner solar system, the activity of Garradd was complex and changed significantly during the time it was observed.

Reference
Bodewits D, Farnham TL, A’Hearn MF, Feaga LM, McKay A, Schleicher DG and Sunshine JM (2014) The Evolving Activity of the Dynamically Young Comet C/2009 P1 (Garradd). The Astrophysical Journal 786:48.
[doi:10.1088/0004-637X/786/1/48]

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