Cometary Science Newsletter

Issue
27
Month
June 2017
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

SBAG Steering Committee Candidate Solicitation

The Small Bodies Assessment Group Steering Committee, composed of members representing the diverse nature of the small-bodies community, organizes SBAG meetings, drafts and edits findings relating to topics of interest, and provides input to NASA on topics relating to the science of small bodies (use of small bodies in support of human space activities, technology relating to the exploration and utilization of small bodies, and planetary defense). Each member serves a multi-year term. We are currently looking for candidates for four open positions on the Steering Committee in the following areas:

  • SBAG Human Exploration Lead - The Human Exploration Lead serves as a Steering Committee member and leads SBAG activities relating to topics of human exploration, as well as work with SBAG’s Human Exploration liaisons. This is a three-year term.
  • Two members with any expertise relevant to SBAG - The Steering Committee tries to maintain a balance of expertise while representing a broad cross-section of the small bodies community. The SBAG seeks potential members who are interested in small body topics, regardless of specific expertise, although would be particularly interested in adding at least one member whose focus is on TNO/KBO objects. These positions are three-year terms.
  • Early Career Secretary – We encourage the participation of scientists and engineers early in their careers. The Early Career Secretary will assist with meeting and website logistics, as well as serve as a full member of the Steering Committee. We invite graduate students, postdocs, and other early career scientists or engineers (within 3 years of PhD/MS/BS) to apply. This is a two-year term.

To indicate your willingness to serve in any of these positions, please email Tim Swindle (tswindle@lpl.arizona.edu) by June 9, 2017, and include a two- to four-page CV. Selection will be made at the 17th Meeting of SBAG, June 12-14, 2017.

Refereed Articles

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

  • Ye, Q.-Z. 1
  1. Caltech

Dormant or near-dormant short-period comets can unexpectedly regain the ability to eject dust. In many known cases, the resurrection is short-lived and lasts less than one orbit. However, it is possible that some resurrected comets can remain active in later perihelion passages. We search the archival images of various facilities to look for these "reactivated" comets. We identify two candidates, 297P/Beshore and 332P/Ikeya–Murakami, both of which were found to be inactive or weakly active in the previous orbit before their discovery. We derive a reactivation rate of ~0.007 comet-1 orbit-1, which implies that typical short-period comets only become temporarily dormant a few times or less. Smaller comets are prone to rotational instability and may undergo temporary dormancy more frequently. Next generation high-cadence surveys may find more reactivation events of these comets.

The Astronomical Journal (Published)

NASA ADS: 2017AJ....153..207Y arXiv: 1703.06997

Abundances and spatial distributions of H2O and CO2 at comet 9P/Tempel 1 during a natural outburst

  • Moretto, M. J. 1
  • Feaga, L. M. 1
  • A'Hearn, M. F. 1
  1. University of Maryland

On approach to comet 9P/Tempel 1, Deep Impact observed about a dozen natural outbursts. One of the largest occurred on 2 July 2005 and was also captured by Deep Impact's infrared spectrometer, HRI-IR. HRI-IR operates between 1.05 and 4.86 μm, allowing it to detect H2O (2.67 μm) and CO2 (4.27 μm) emission bands simultaneously. In the hours leading up to the outburst, both H2O and CO2 behaved quiescently, consistent with previously published studies. During the outburst, CO2 abundance increased by 40% while H2O abundance stayed constant. No additional species were detectable during the outburst. The distribution of CO2 during the outburst is correlated with that of the dust, observed at the same time in the visible. The abundance of CO2 returned to quiescent levels within 3.6 h of outburst onset. A slight enhancement in H2O was observed well after the outburst, though this does not appear to be correlated with the outburst. From this analysis, it is likely that CO2 was a driver of the 2 July 2005 outburst and that H2O was not.

Icarus (In press)

DOI: 10.1016/j.icarus.2017.05.013

Analog Experiments on Tensile Strength of Dusty and Cometary Matter

  • Musiolik, G. 1
  • de Beule, C. 1
  • Wurm, G. 1
  1. University of Duisburg-Essen, Faculty of Physics, Germany

The tensile strength of small dusty bodies in the solar system is determined by the interaction between the composing grains. In the transition regime between small and sticky dust (μm) and non cohesive large grains (mm), particles still stick to each other but are easily separated. In laboratory experiments we find that thermal creep gas flow at low ambient pressure generates an overpressure sufficient to overcome the tensile strength. For the first time it allows a direct measurement of the tensile strength of individual, very small (sub)-mm aggregates which consist of only tens of grains in the (sub)-mm size range. We traced the disintegration of aggregates by optical imaging in ground based as well as microgravity experiments and present first results for basalt, palagonite and vitreous carbon samples with up to a few hundred Pa. These measurements show that low tensile strength can be the result of building loose aggregates with compact (sub)-mm units. This is in favour of a combined cometary formation scenario by aggregation to compact aggreates and gravitational instability of these units.

Icarus (In press)

DOI: 10.1016/j.icarus.2017.05.009

The Rosetta mission orbiter science overview: the comet phase

  • Taylor, M.G.G.T. 1
  • Altobelli, N. 2
  • Buratti, B.J. 3
  • Choukroun, M. 3
  1. ESA/ESTEC, 2201 AZ Noordwijk, The Netherlands
  2. ESA/ESAC, 28692 Villanueva de la Cañada, Spain
  3. JPL/California Institute of Technology, Pasadena, CA 91109, USA

The international Rosetta mission was launched in 2004 and consists of the orbiter spacecraft Rosetta and the lander Philae. The aim of the mission is to map the comet 67P/Churyumov–Gerasimenko by remote sensing, and to examine its environment in situ and its evolution in the inner Solar System. Rosetta was the first spacecraft to rendezvous with and orbit a comet, accompanying it as it passes through the inner Solar System, and to deploy a lander, Philae, and perform in situ science on the comet’s surface. The primary goals of the mission were to: characterize the comet’s nucleus; examine the chemical, mineralogical and isotopic composition of volatiles and refractories; examine the physical properties and interrelation of volatiles and refractories in a cometary nucleus; study the development of cometary activity and the processes in the surface layer of the nucleus and in the coma; detail the origin of comets, the relationship between cometary and interstellar material and the implications for the origin of the Solar System; and characterize asteroids 2867 Steins and 21 Lutetia. This paper presents a summary of mission operations and science, focusing on the Rosetta orbiter component of the mission during its comet phase, from early 2014 up to September 2016. This article is part of the themed issue ‘Cometary science after Rosetta’.

Philosophical Transactions Of the Royal Society A (Published)

DOI: 10.1098/rsta.2016.0262