Observational Characterization of Recurrently Active Main-Belt Comets and Near-Earth Main-Belt Comet Candidates

NASA Solar System Observations Program

Other Non PSI Personnel: Masateru Ishiguro (Seoul U), Nicholas Moskovitz (Lowell Obs), Chad Trujillo (NAU), Jana Chesley (JPL), Scott Sheppard (Carnegie I), Matthew Knight (UMD), Audrey Thirouin (Lowell Obs)

Start Date: 04/16/2019
Project #: 1641
End Date: 04/15/2024
Award #: 80NSSC19K0869

PSI Co-Investigators and Collaborators

Project Description

We propose to continue a long term observational campaign to characterize main belt comets (MBCs), which we have been monitoring regularly since their discoveries, and conduct a new investigation of a group of possibly related objects. For the first portion of our project, we will monitor and analyze the active phases of the MBCs that exhibit activity during the project period, characterize the evolution of that activity, and characterize MBC nucleus properties. For the second portion of our project, we will observationally characterize the nuclei and activity of apparent Jupiter family comets (JFCs) that have been identified as potentially originating in the asteroid belt (leading us to refer to them as possible “near Earth MBCs”, or NEMBCs), and determine whether physical evidence supports their proposed main belt origins.

Active asteroids are rare objects that have asteroid like orbits, yet display comet like activity. They consist of MBCs, which display cometary activity indicative of sublimating ice (Hsieh & Jewitt 2006), and disrupted asteroids, which exhibit dust emission that mimics cometary activity but is actually caused by impacts or rotational destabilization. MBCs can be distinguished from disrupted asteroids using indirect methods such as dust modeling indicating the action of prolonged emission events or observations of repeated activity, where the latter is considered one of the strongest indications of sublimation driven activity in an active asteroid. Dynamical analyses suggest that MBCs are native to the main belt, where the existence of present day ice in the asteroid belt is significant given that icy asteroids may have been an important primordial source of terrestrial water (O’Brien et al. 2018).

Seven of the MBCs we will study have exhibited recurrent activity, validating early assessments of the drivers of their activity. Monitoring of upcoming activity will let us track changes in activity strength over time, helping... activity strength over time, helping to constrain active lifetimes. We will use dust modeling to determine mass loss rates, total mass loss, ejection times, ejection speeds, and particle size distributions from both new and archival observations.

Meanwhile, Fernandez & Sosa (2015) identified a number of apparent JFCs that are more dynamically stable and exhibit weaker activity than other JFCs, and suggested that these objects might originate in the main asteroid belt. This hypothesis was supported by Hsieh & Haghighipour (2016) who found that near Earth objects from the main belt could acquire JFC like orbits in certain situations. If some of those objects were icy (i.e., dormant MBCs), they could become active and mimic JFCs from the outer solar system, becoming what we refer to as NEMBCs.

We will conduct observations to photometrically, morphologically, and spectroscopically characterize the activity and nuclei of NEMBC candidates, and determine if there is evidence that these objects are from the asteroid belt. Confirmation that NEMBCs are from the main belt would be a major advancement as it could allow for the spectroscopic detection and characterization of sublimation products from an icy object from the main belt, a key goal of MBC research.

Observations will be conducted with a range of telescopes, particularly Gemini North and South, Lowell Observatory’s Discovery Channel Telescope, the Magellan telescopes, the Palomar 5.1m Hale Telescope, the JPL 1.0m telescope on Table Mountain, and the European Southern Observatory’s VLT, on many of which we have a history of being awarded time.

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