Cometary Science Newsletter

Comets Symposium and Rosetta SWT 2016: Registration

The international conference on cometary science entitled "Comets: A new vision after Rosetta/Philae" will be held November 14-18, 2016, at the Abattoirs Museum in Toulouse, France. The 46th Rosetta Science Working Team technical session will be held on Friday.

The program is now available online on the conference website:

http://www.comets2016toulouse.com

More technical details - poster size, talks format - will be soon sent to the authors.

The early registration deadline with the best rates (150 euros instead of 250 euros) is 14 October. The registration fee includes access to all sessions, coffee breaks and to a cocktail gala dinner scheduled on Tuesday (with an extra fee for accompanying persons). All needed information for venue and accomodation are provided on the above website.

If you have questions or need assistance during the registration process, please send an email to contact@comets2016toulouse.com and reference Comets 2016 in the subject.

The Organising Committee

Comet Wirtanen - Observers' Workshop at DPS

The Comet Group at the University of Maryland is organizing a campaign to coordinate observations of Comet 46P/Wirtanen during its 2018 apparition. To kick off this campaign, we are holding a short workshop at the DPS meeting in Pasadena to raise awareness of this opportunity, and to assemble participants who may be interested in collaborations and coordinated studies, as well as public outreach and educational opportunities. The meeting will be held during the lunch break on Monday, October 17, from 12:30-2:00 in Room C102 in the Pasadena Convention Center.

Comet Wirtanen is a small, hyperactive comet, which in many respects is a near-twin of comet 103P/Hartley 2. It will pass within 0.077 AU of the Earth on December 16, 2018, just four days after reaching perihelion. This close approach is the highlight of an already excellent apparition, which offers prime conditions for high-resolution imaging, favorable circumstances for spectroscopic observations, and visibility allowing coverage for many hours per night for over a year around perihelion.

As the original target of the Rosetta mission and the target of the Comet Hopper Discovery Phase A mission proposal, Wirtanen is clearly a potential future spacecraft target. The upcoming apparition presents us with the opportunity to study this comet in a long-duration, systematic manner encompassing a wide range of techniques and wavelength regimes, to further characterize its physical and chemical properties, to investigate its long-term evolution through comparison to past data sets, and to perform comparative studies with Hartley 2 and other comets. This bright target also represents an opportunity to mobilize the amateur observing community to execute otherwise difficult-to-achieve science programs.

For more information, contact Tony Farnham (farnham@astro.umd.edu).

Fragmentation Kinematics in Comet 332P/Ikeya-Murakami

• Jewitt, David ¹
• and 11 co-authors^null

1. UCLA

We present initial time-resolved observations of the split comet 332P/Ikeya-Murakami taken using the Hubble Space Telescope. Our images reveal a dust-bathed cluster of fragments receding from their parent nucleus at projected speeds in the range 0.06 to 3.5 m/s from which we estimate ejection times from October to December 2015. The number of fragments with effective radii ≳20 m follows a differential power law with index g = -3.6+/-0.6, while smaller fragments are less abundant than expected from an extrapolation of this power-law. We argue that, in addition to losses due to observational selection, torques from anisotropic outgassing are capable of destroying the small fragments by driving them quickly to rotational instability. Specifically, the spin-up times of fragments <20 m in radius are shorter than the time elapsed since ejection from the parent nucleus. The effective radius of the parent nucleus is r_e < 275 m (geometric albedo 0.04 assumed). This is about seven times smaller than previous estimates and results in a nucleus mass at least 300 times smaller than previously thought. The mass in solid pieces, 2x10^9 kg, is about 4 percent of the mass of the parent nucleus. As a result of its small size, the parent nucleus also has a short spin-up time. Brightness variations in time-resolved nucleus photometry are consistent with rotational instability playing a role in the release of fragments.

Astrophysical Journal Letters (Published)

DOI: 10.3847/2041-8205/829/1/L8 arXiv: 1609.04452