Cometary Science Newsletter

Issue
68
Month
November 2020
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

Round-table discussion of comet narrowband filters

Following a lively Slack discussion at DPS about comet narrowband filters, it appears there is significant community interest in having a broader discussion about the status and future availability of these filters. If you are interested in being involved in the discussion, please indicate your interest by filling out this Google form by November 15.

Matthew Knight (astromatthew@gmail.com)

Refereed Articles

Abstracts of articles in press or recently published. Limited to 3000 characters.

Outbursting Quasi-Hilda Asteroid P/2010 H2 (Vales)

  • Jewitt, David 1
  • Kim, Yoonyoung 2
  1. UCLA
  2. Max Planck Institute for Solar System Research

Quasi-Hilda asteroid P/2010 H2 (Vales) underwent a spectacular photometric outburst by 7.5 magnitudes (factor of 1e3) in 2010. Here, we present our optical observations of this event in the four month period from April 20 to August 10. The outburst, starting UT 2010 April 15.76, released dust particles of total cross-section 17,600 km2 (albedo 0.1 assumed) and mass 1.2e9 kg, this being about 1e-4 of the mass of the nucleus, taken as a sphere of radius 1.5 km and density 500 kg/m3. While the rising phase of the outburst was very steep (brightness doubling time of hours), subsequent fading occurred slowly (fading timescales increasing from weeks to months), as large, low velocity particles drifted away from the nucleus. A simple model of the fading lightcurve indicates that the ejected particles occupied a broad range of sizes, from microns to centimeters and followed a differential power-law distribution with index 3.6+/-0.1 (similar to that in other comets). The fastest particles had speeds 210 m/s, indicating gas-drag acceleration of small grains well-coupled to the flow. Low energy processes known to drive mass loss in active asteroids, including rotational disruption, thermal and desiccation stress cracking, and electrostatic repulsion, cannot generate the high particles speeds measured in P/Vales, and are discounted. Impact origin is unlikely given the short dynamical lifetimes of the quasi-Hildas and the low collision probabilities of these objects. The specific energy of the ejecta is estimated at 220 J/kg. The outburst follows a series of encounters with Jupiter in the previous century, consistent with the delayed activation of buried supervolatiles (and/or the crystallization of sub-surface amorphous ice) by conducted heat following an inward displacement of the perihelion. A potential origin in the debris cloud produced by avalanche is also considered.

The Planetary Science Journal (In press)

arXiv: 2010.05012

Component properties and mutual orbit of binary main-belt comet 288P/(300163) 2006 VW 139

  • Agarwal, J. 1,2
  • Kim, Y. 1
  • Jewitt, D. 3,4
  • Mutchler, M. 5
  • Weaver, H. 6
  • Larson, S. 7
  1. Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
  2. Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Germany
  3. Department of Earth, Planetary and Space Sciences, UCLA, Los Angeles, USA
  4. Department of Physics and Astronomy, UCLA, Los Angeles, USA
  5. Space Telescope Science Institute, Baltimore, USA
  6. The Johns Hopkins University Applied Physics Laboratory, Laurel, USA
  7. Lunar and Planetary Laboratory, University of Arizona, Tucson, USA

The binary asteroid 288P/(300163) is unusual both for its combination of wide-separation and high mass ratio and for its comet-like activity. It is not currently known whether there is a causal connection between the activity and the unusual orbit or if instead the activity helped to overcome a strong detection bias against such sub-arcsecond systems. We aim to find observational constraints discriminating between possible formation scenarios and to characterise the physical properties of the system components. We measured the component separation and brightness using point spread function fitting to high-resolution Hubble Space Telescope/Wide Field Camera 3 images from 25 epochs between 2011 and 2020. We constrained component sizes and shapes from the photometry, and we fitted a Keplerian orbit to the separation as a function of time. Approximating the components A and B as prolate spheroids with semi-axis lengths a<b and assuming a geometric albedo of 0.07, we find a_A < 0.6 km, b_A > 1.4 km, a_B < 0.5 km, and b_B > 0.8 km. We find indications that the dust production may have concentrated around B and that the mutual orbital period may have changed by 1-2 days during the 2016 perihelion passage. Orbit solutions have semi-major axes in the range of (105-109) km, eccentricities between 0.41 and 0.51, and periods of (117.3-117.5) days pre-perihelion and (118.5-119.5) days post-perihelion, corresponding to system masses in the range of (6.67-7.23) x 10^12 kg. The mutual and heliocentric orbit planes are roughly aligned. Based on the orbit alignment, we infer that spin-up of the precursor by the YORP effect led to the formation of the binary system. We disfavour (but cannot exclude) a scenario of very recent formation where activity was directly triggered by the break-up, because our data support a scenario with a single active component.

Astronomy & Astrophysics (In press)

arXiv: 2009.13844