Multi-spacecraft study of the activity of comet 249P/LINEAR near perihelion from 1997-2020

Comet 249P/LINEAR is an unusual Jupiter-family comet (JFC): despite having a perihelion distance of 0.5 AU and frequently passing within 0.4 AU of Earth in the 20th century (including <0.1 AU in 1997), it was not discovered until 2006. Subsequent dynamical analysis (Fernandez & Sosa 2015) revealed that it is on a more stable orbit than most JFCs, and may have originated from the asteroid belt. 249P is weakly active, with activity apparently confined to about 20 days around perihelion (Fernandez et al. 2017). The cause of its low activity is not yet understood, though it could plausibly be due to having formed amongst the asteroids or an evolutionary depletion of volatiles from having spent >10⁴ years in the inner solar system.

249P has frequently passed through the fields of view of various solar observatories when near perihelion. Its most favorable apparition to date came in 2020 (perihelion June 29) when it was successfully observed by SOHO from June 16-21 (heliocentric distance, r = 0.58-0.52 AU; cometocentric distance, delta = 0.44-0.49 AU; phase angle = 163-171 deg), Parker Solar Probe on June 28 (r = 0.50 AU; delta = 0.11 AU; phase = 120 deg), and STEREO-A from July 2-16 (r = 0.50-0.62 AU; delta = 1.18-1.46 AU; phase = 53-28 deg). In addition, it was well observed by STEREO-A in April 2011 (r = 0.57-0.52 AU; delta = 0.46-0.44 AU; phase = 135-166 deg) and was not detected by SOHO despite highly favorable viewing geometry in May 1997 (r = 0.79-0.73 AU; delta = 0.20-0.27 AU; phase = 168-171 deg). It was also not detected by SOHO and STEREO on several other apparitions at less favorable viewing geometries.

We will utilize photometry and, when possible, morphology from these observations to constrain the level and extent of 249P’s activity and compare our results with estimates made from Earth-based observations. The very different viewing geometries at which it was observed in 2020 will also allow us to compare its dust phase function to that of other comets to look for clues to its origin. Results from this study will be valuable for planning observations and possible missions during its exceptional close approach to Earth (0.057 AU) in 2029.

This work is supported by NASA’s Solar System Observations Program grant 80NSSC19K0869 and Solar System Workings Program grant 80NSSC19K0024.