C/2017 U7 (PanSTARRS)

For other comets of the same name, see List of Pan-STARRS discoveries.

C/2017 U7 (PanSTARRS)

The orbit of C/2017 U7 (PanSTARRS)
Discovery
Discovered by	Pan-STARRS
Discovery site	Haleakala Observatory
Discovery date	29 October 2017
Designations
MPC designation	C/2017 U7, A/2017 U7
Alternative designations	P10EwQh
Orbital characteristics
Epoch	8 January 2020 (JD 2458856.5)
Observation arc	176 days
Earliest precovery date	18 August 2017
Perihelion	6.418 AU
Semi-major axis	~9,500 AU (inbound)
Eccentricity	0.99932 (inbound) 1.00012 (outbound)
Orbital period	~920,000 years (inbound)
Inclination	142.64°
Longitude of ascending node	276.23°
Argument of periapsis	326.07°
Last perihelion	11 September 2019
Earth MOID	5.467 AU
Jupiter MOID	1.634 AU
Physical characteristics
Mean radius	22.5 km (14.0 mi)
Geometric albedo	0.04 (assumed)
Comet total magnitude (M1)	6.1
Apparent magnitude	15.0 (2020 apparition)

C/2017 U7 (PanSTARRS) is a hyperbolic comet (previously classified as A/2017 U7, a hyperbolic asteroid), first observed on 29 October 2017 by astronomers of the Pan-STARRS facility at the Haleakala Observatory, Hawaii, United States when the object was 7.8 AU (1.2 billion km) from the Sun. Despite being discovered only 10 days after interstellar asteroid 1I/'Oumuamua, it was not announced until March 2018 (along with C/2018 C2 (Lemmon), which was believed to be another hyperbolic asteroid at the time) as its orbit is not strongly hyperbolic beyond most Oort Cloud comets. As of August 2018, there is only 1 hyperbolic asteroid known, 1I/ʻOumuamua, but hundreds of hyperbolic comets are found.

Orbit

Although C/2017 U7's orbit is no longer bound to the Solar System, unlike ʻOumuamua, it is probably not an interstellar object. It had an inbound orbital period of roughly 800,000 years. Its point of origin is inclined only 3.5 degrees from the galactic plane, but its aphelion points roughly to the Galactic anticenter, so if it did somehow originate from interstellar space with a typical Solar System velocity (which is highly unlikely) it would have been traveling on an unusual orbit directly into the galactic core from beyond the Sun's orbit around the Milky Way.

A barycentric orbit of C/2017 U7, however, shows that it 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. It had an inbound orbital period of roughly 920,000 years until the current approach to the Solar System, where perturbations show it on an extremely weak hyperbolic trajectory after leaving the planetary region of the Solar System. The barycentric eccentricity increases above 1 starting with an epoch of July 2022, reaching 1.00012 once it gets beyond planetary perturbations.

As of March 2018, C/2017 U7 was inbound 7.4 AU (1.1 billion km) from the Sun. C/2017 U7 makes closest approach to the Sun on 10 September 2019 at a distance of 6.4 AU (outside of Jupiter's orbit). Due to the orbital inclination, on 18 May 2020, the asteroid will be about 1.66 AU (248,000,000 km; 154,000,000 mi) from Jupiter, generating a peak heliocentric eccentricity at 1.003. The dynamical analysis shows that the object has probably originated in the Oort cloud, however an interstellar origin cannot be discarded.

• 
  Path across sky
• 
  Hyperbolic trajectory through solar system

Physical characteristics

The spectra and the colors of the hyperbolic comet C/2017 U7 (PanSTARRS) are atypical and the feature and overall spectral shape can be reproduced by laboratory spectra of kerite, a template for aliphatic-rich hydrocarbons that has been previously identified in NIR cometary spectra absorptions.

With an absolute magnitude of $\,H\,=(\;10.87\pm \;0.13)$ corresponding to a nucleus diameter of 45 km (28 mi), this made C/2017 U7 as one of the largest comets ever known, assuming a geometric albedo of 0.04.

External links

• C/2017 U7 at the JPL Small-Body Database