C/2017 U7 (PanSTARRS)
Hyperbolic comet discovered days after 1I/'Oumuamua, likely from Oort Cloud.
C/2017 U7 (PanSTARRS) is a hyperbolic comet first observed on 29 October 2017 by astronomers at the Pan-STARRS facility at the Haleakala Observatory in Hawaii. It is notable for being discovered only 10 days after interstellar asteroid 1I/'Oumuamua, though its orbit is not strongly hyperbolic beyond most Oort Cloud comets, and it was initially classified as a hyperbolic asteroid.
Quick Facts
- Discoverer
- Pan-STARRS
- Discovery Site
- Haleakala Observatory
- Discovery Date
- 29 October 2017
- Mpc Name
- C/2017 U7, A/2017 U7
- Designations
- P10EwQh
- Orbit Ref
- barycenter · jpldata
- Epoch
- 8 January 2020 (JD 2458856.5)
- Observation Arc
- 176 days
- Earliest Precovery Date
- 18 August 2017MPC
- Perihelion
- 6.418 AU
- Semimajor
- ~9,500 AU (inbound)
- Eccentricity
- 0.99932 (inbound) / 1.00012 (outbound)
Facts from the source article.
Lore & Background
C/2017 U7 was first observed on 29 October 2017 by astronomers of the Pan-STARRS facility at the Haleakala Observatory, Hawaii, when the object was 7.8 AU from the Sun. Despite being discovered only 10 days after interstellar asteroid 1I/'Oumuamua, it was not announced until March 2018, as its orbit is not strongly hyperbolic beyond most Oort Cloud comets. Its inbound orbital period was roughly 800,000 years until the current approach to the Solar System, where perturbations show it on an extremely weak hyperbolic trajectory after leaving the planetary region, and its point of origin is inclined only 3.5 degrees from the galactic plane, with its aphelion pointing roughly to the Galactic anticenter. A barycentric orbit analysis shows that C/2017 U7 is only a very distant Solar System object, approaching as far as 16000±1000 AU from the Sun, around the distance of the Oort Cloud. Its inbound orbital period was roughly 920,000 years until the current approach, where perturbations show it on an extremely weak hyperbolic trajectory after leaving the planetary region. The barycentric eccentricity increases above 1 starting with an epoch of July 2022, reaching 1.00012 once beyond planetary perturbations. The dynamical analysis indicates the object probably originated in the Oort cloud, though an interstellar origin cannot be discarded. Physically, the spectra and colors of C/2017 U7 are atypical, and the feature and overall spectral shape can be reproduced by laboratory spectra of kerite, a template for aliphatic-rich hydrocarbons previously identified in NIR cometary spectra absorptions. With an absolute magnitude of 10.87 ± 0.13, corresponding to a nucleus diameter of 45 km, this made C/2017 U7 one of the largest comets ever known, assuming a geometric albedo of 0.04.
Reader's Guide
C/2017 U7 (PanSTARRS) holds significance as a hyperbolic comet discovered in close temporal proximity to the interstellar asteroid 1I/'Oumuamua, yet its orbit is not strongly hyperbolic beyond most Oort Cloud comets. Its delayed announcement until March 2018, alongside C/2018 C2 (Lemmon), underscores the caution in classifying such objects. The comet's barycentric orbit reveals it as a very distant Solar System object, approaching the Oort Cloud at up to 16000±1000 AU, with an inbound period of roughly 920,000 years before perturbations set it on a weak hyperbolic trajectory. Its legacy lies in the ambiguity of its origin: dynamical analysis suggests an Oort Cloud origin, but an interstellar origin cannot be discarded. Physically, its large nucleus diameter of 45 km makes it one of the largest known comets, and its atypical spectra, matching kerite, provide insights into aliphatic-rich hydrocarbons in cometary material. As of August 2018, only one hyperbolic asteroid (1I/'Oumuamua) was known, but hundreds of hyperbolic comets have been found, placing C/2017 U7 within a broader context of weakly hyperbolic objects that challenge clear classification.
More in Named Comets, Part 2 1-24
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