Cometary Science Newsletter

September 2018
Michael S. P. Kelley (

Conference Announcements

Announcements for cometary conferences or workshops. Limited to 2000 characters.

LSST and the Solar System Workshop

Wednesday October 24, 2018 4:30-6:00 pm, 50th DPS meeting, Knoxville, TN - Open to all DPS attendees
Organizers: Meg Schwamb (Gemini Observatory) & David Trilling (NAU)

Over its 10 year lifespan, the Large Synoptic Survey Telescope (LSST) will catalog over 5 million Main Belt asteroids, almost 300,000 Jupiter Trojans, over 100,000 NEOs, over 40,000 KBOs, tens of interstellar objects, and over 10,000 comets. Many of these objects will receive hundreds of observations in multiple bandpasses. The LSST Solar System Science Collaboration (SSSC) is preparing methods and tools to analyze this data, as well as understand optimum survey strategies for discovering moving objects throughout the Solar System.

This workshop serves as the annual meeting of the LSST SSSC, and is open to everyone. We will provide updates on current and future activities within the SSSC. The emphasis will not be on general LSST background but on details relevant to Solar System science topics. In particular, this year discussions and presentations will focus on the development of the LSST Moving Object Processing System (MOPS), the SSSC’s feedback/input on upcoming LSST survey cadence decisions, and future community follow-up opportunities. There will be time set aside for open discussion for both members of the SSSC and the broader planetary community.

Contact Meg Schwamb ( and David Trilling ( with any questions.

Refereed Articles

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

Two Hyperbolic Baldheads in the Solar System: 2017 U7 and 2018 C2

  • Hui, Man-To 1
  1. Earth, Planetary and Space Sciences, UCLA

We present a study of two newly discovered heliocentric hyperbolic objects—2017 U7 and 2018 C2. Both are possibly thermally evolved comets. Observations of the latter in 2018 March from Xingming Observatory revealed that it has a color similar to those of the long-period comets, Trojans, and D-type asteroids: mB − mV = 0.75 ± 0.03, mV − mR = 0.41 ± 0.02, and mR − mI = 0.37 ± 0.03. A possible extremely faint coma of ~9" across was observed. The radial profile of 2018 C2 in comparison with those of the field stars helps confirm its cometary nature. Based on our convolution model, its mass-loss rate is estimated to be 0.7 ± 0.2 kg s−1. Assuming geometric albedo pR = 0.04, its effective radius is 4.4 ± 0.5 km, which means that the fraction of active area is merely ~10−5–10−4. Our N-body dynamical simulations show that both objects are most likely dynamically old members from the Oort cloud. 2017 U7 has a ~60% chance to escape the solar system in the 1.5 Myr following its current perihelion passage due to a moderate close encounter with Jupiter in 2020 May. On the condition that no disintegration occurs, 2018 C2 will revisit the inner solar system 0.13–0.14 Myr later, with perihelion distance ~2 au.

Astronomical Journal (Published)

DOI: 10.3847/1538-3881/aacdf3 arXiv: 1806.06904

Is the Cometary Nucleus-extraction Technique Reliable?

  • Hui, Man-To 1
  • Li, Jian-Yang 2
  1. Earth, Planetary and Space Sciences, UCLA
  2. Planetary Science Institute

We investigated the reliability of the cometary nucleus-extraction technique, and found the answer to this question: it depends. Our experiment reveals that, given an optically thin coma, generally, the smaller the signal ratio of nucleus to coma, the less reliable the cometary nucleus-extraction technique is. We strongly suggest the technique only be applied to cases where the nucleus signal occupies ≳10% of the total signal wherein the bias is no more than a few percent. Otherwise, there is probably no way to debias results from this technique in reality, as its reliability is highly sensitive to entangling complications, including the coma profile, and the point-spread function (PSF).

Publications of the Astronomical Society of the Pacific (Published)

DOI: 10.1088/1538-3873/aad538 arXiv: 1807.07993

Coma Morphology, Numerical Modeling, and Production Rates for Comet C/Lulin (2007 N3)

  • Allison N. Bair 1
  • David G. Schleicher 1
  • Matthew M. Knight 2
  1. Lowell Observatory, Flagstaff, AZ
  2. Department of Astronomy, University of Maryland, College Park, MD

We report on narrowband photometry and extensive imaging observations of comet C/Lulin (2007 N3) obtained at Lowell Observatory during 2008 and 2009. Enhanced CN images revealed a double corkscrew morphology with two near-polar jets oriented approximately east-west, and both CN and dust images showed nightly rotational variability and seasonal changes in bulk morphology. We determined a rotational pole direction of RA/Dec = 81°/+29° with an obliquity of 97°, and a sidereal rotation period of 41.45 ± 0.05 hr. Monte Carlo numerical modeling best replicated the observed CN features with an eastern source area at lat/long -80°/125° and a ∼10° radius and a western source area at lat/long +77°/245° and a ∼20° radius, ∼4× larger than the eastern source. An additional small, near-equatorial source was necessary to reproduce some dust features. Water morphology, based on OH, was quite different than that of the carbon-bearing species, implying a different driver for the polar jets such as CO or CO2. Ion tails were detected in decontaminated images from both the dust and NH filters, likely being H2O+ and OH+, respectively. We measured water production both before and after perihelion, and extrapolate peak water production at perihelion to be about 1.0 × 1029 molecules s-1. We estimate an active fraction of only 4-5% and a nucleus radius of up to ~8 km. Our data suggest that Lulin, defined as dynamically new in a statistical sense, behaves more like a long-period comet due to its nearly asteroidal early appearance, isolated source regions, and dust properties.

The Astronomical Journal (In press)

arXiv: 1807.11867