# C/2019 Q4 (Borisov)

(Redirected from Gb00234)
Discovery C/2019 Q4 is an interstellar cometfrom outside the Solar System(animated comet nears inner Solar System) L51 (Gennady Borisov) 30 August 2019 gb00234 2019-Sep-09[1] 14 days 147 2.09±0.03 au −0.77±0.03 au 3.70±0.12 (JPL)3.54±0.10 (Gray)[2]2–4 (Scout)[3] 43.4°±0.2° 308.8°±0.2° 207.4°±0.5° ≈1.16 au[1] ≈2–16 km[4] ≈6 December 2019[1]

C/2019 Q4 (Borisov) (internal name gb00234) is an interstellar comet with a heliocentric orbital eccentricity of ≈3 and is not bound to the Sun.[1][5][6][7] The hyperbolic excess velocity (${\displaystyle v_{\infty }}$) of about 34 km/s is an important indicator that it is interstellar[8][9] as a ${\displaystyle v_{\infty }}$ under 3 km/s can be explained by perturbations.

## Discovery

The object was discovered on 30 August 2019 at MARGO, Nauchnij by Ukrainian amateur astronomer Gennady Borisov using his custom-built 0.65-meter telescope.[10] At discovery, it was inbound 3±0.1 au from the Sun, 3.8±0.1 au from Earth, and had a solar elongation of 38°.[11] It came from the direction of Perseus near the border with Cassiopeia and very close to the galactic plane. It will come to perihelion (closest approach to the Sun) around 6 December 2019.[1]

## NEOCP

The comet was listed on the near-Earth object confirmation page (NEOCP) as gb00234 because orbit solutions had the possibility of it making notable approaches to Earth. Before the uncertainties were reduced enough to know the comet was hyperbolic (e>1) and 3 au from the Sun, orbit solutions suggested it could be 1.4 au from the Sun, have an aphelion (furthest distance from the Sun) of 1.6 au, and orbit the Sun in less than 1 year.[12] Such a solution came from exchanging eccentricity for inclination, ie: higher inclination of 75° with a lower eccentricity of 0.7. Such an orbit is now known to be invalid.

## Eccentricity

The smaller the perihelion point, the smaller the eccentricity will be.[13] Interstellar flybys can have very high eccentricities such as e > 3 because the objects were never bound to the Sun and a small change in velocity will result in a large change in the eccentricity.

With a 13-day observation arc, a best-fit for the hyperbolic orbit has an eccentricity of about 3.5, with perihelion at 2.0 au around 7 December 2019.[2] Using 151 observations, JPL's Scout gave an eccentricity range of 2.9–4.5.[3]

With an observation arc of only 12 days, there was still some doubt to if it was interstellar. But the orbit could only be parabolic if it is significantly affected by non-gravitational forces (outgassing thrust) more than any other known comets.[9] Using large non-gravitational forces on the highly eccentric orbit solution could generate an eccentricity of about 1, an Earth-MOID of 0.34 au (51 million km), with perihelion at 0.90 au around 30 December 2019.[14] But the orbit converged to the hyperbolic solution which indicated an interstellar origin and non-gravitational forces could not explain the motion.[5]

Interstellar velocity inbound
Object Velocity
C/2010 X1 (Elenin)
(For comparison when
200AU from the Sun)
2.96 km/s[15]
0.62 au/year
1I/2017 U1 (ʻOumuamua) 26.33 km/s[16]
5.55 au/year
C/2019 Q4 (Borisov) 30.7 km/s[9]
6.47 au/year
JPL Scout eccentricity ranges[17]
# of
observations
Observation
arc (hours)
Eccentricity
range
81 225 0.9 – 1.6
99 272 2.0 – 4.2
127 289 2.8 – 4.7
142 298 2.8 – 4.5
151 302 2.9 – 4.5

Currently it is a better northern hemisphere object.[2] Due to the 44 degree orbital inclination, C/2019 Q4 does not make any notable close approaches to the planets.[1] Around 6 December 2019 the comet will be an equal distance from the Sun and Earth.[2] In late December it will be about 2 au from Earth and have a solar elongation of about 80°.[2] By the new year it will be a better southern hemisphere object.[2]

Comet C/2019 Q4 (Borisov) – orbit diagrams
September 14, 2019
Trajectory
Trajectory comparison with Oumuamua.

## Reachability

The higher hyperbolic excess velocity of C/2019 Q4 of 30.7 km/s makes it harder to reach for a spacecraft than 1I/'Oumuamua (26.33 km/s). According to a team of the Initiative for Interstellar Studies, a two-ton spacecraft could theoretically have been sent in July 2018 to intercept with C/2019 Q4 using a Falcon Heavy-class launcher, but only if the object had been discovered much earlier than it was.[18] Launches after the actual discovery date would require a significantly large launcher such as the Space Launch System, a combined Jupiter flyby and an Oberth manoeuvre. And even a SLS-class launcher would now only be able to deliver a 3kg payload (such as a CubeSat) to a trajectory that intercepted C/2019 Q4. According to congressional testimony, NASA may need at least five years to launch such an intercepting mission.[19]

## Composition

On 13 September 2019, the Gran Telescopio Canarias obtained the visible (low-resolution) spectrum of C/2019 Q4 (Borisov) that revealed that this object has a surface composition not very different from that found in typical Oort Cloud comets.[20]

## References

1. "JPL Small-Body Database Browser: C/2019 Q4 (Borisov)". Jet Propulsion Laboratory. Archived from the original on 2019-09-11. Retrieved 2019-09-11.
2. Bill Gray. "Pseudo-MPEC for gb00234". Project Pluto. Archived from the original on 2019-09-11. Retrieved 2019-09-11.
3. ^ a b "Scout: gb00234". JPL CNEOS. Archived from the original on 2019-09-10. Retrieved 2019-09-10. (archive.is with 151 obs)
4. ^ Newly Discovered Comet Is Likely Interstellar Visitor NASA, September 12, 2019
5. ^ a b "COMET C/2019 Q4 (Borisov)". Minor Planet Center. Retrieved 2019-09-11.
6. ^ Guzik, Piotr; et al. (12 September 2019). "Interstellar comet 2I/Borisov". arxiv. arXiv:1909.05851v1. Retrieved 13 September 2019.
7. ^ Overbye, Dennis (12 September 2019). "The Maybe Comet From Another Star - Now zinging through Cancer: a glob of light from interstellar space?". The New York Times. Retrieved 13 September 2019.
8. ^ "Interstellar Comet gb00234". Astronomer's Telegram. Archived from the original on 2019-09-12. Retrieved 2019-09-12.
9. ^ a b c Bill Gray. "Is gb00234 an Interstellar Comet or Asteroid". Minor Planet Mailing List. Retrieved 2019-09-10.
10. ^ King, Bob (11 September 2019). "Is Another Interstellar Visitor Headed Our Way?". Sky & Telescope. Retrieved 12 September 2019.
11. ^ Bill Gray. "Pseudo-MPEC for gb00234 (precovery-eph)". Project Pluto. Archived from the original on 2019-09-12. Retrieved 2019-09-11.
12. ^ Bill Gray. "Pseudo-MPEC for gb00234 (AutoNEOCP)". Project Pluto. Archived from the original on 2019-09-10. Retrieved 2019-09-13.
13. ^ eccentricity = (a-q)/a so the smaller perihelion (q), the smaller the eccentricity.
14. ^ Bill Gray. "Pseudo-MPEC for gb00234 (non-grav A1+A2)". Project Pluto. Archived from the original on 2019-09-11. Retrieved 2019-09-11.
15. ^ Comet Elenin was inbound 200 AU from the Sun on 1798-Sep-29. Computed using JPL Horizons Observer Location: "@sun" (deldot is relative motion in km/s and a negative deldot means the target is moving toward the observer.)
16. ^ "Pseudo-MPEC for A/2017 U1 (FAQ File)". Bill Gray of Project Pluto. 26 October 2017. Retrieved 26 October 2017.
17. ^ Scout: gb00234 at Archive.is: (81 obs / 225 hours) (99 obs / 272 hours) (127 obs / 289 hours) (142 obs / 298 hours) (151 obs / 302 hours)
18. ^ Hibberd, Adam; et al. (12 September 2019). "Sending a Spacecraft to Interstellar Comet C/2019 Q4 (Borisov)". arxiv. Retrieved 13 September 2019.
19. ^ U.S.Congress (19 March 2013). "Threats From Space: a Review of U.S. Government Efforts to Track and mitigate Asteroids and Meteors (Part I and Part II) – Hearing Before the Committee on Science, Space, and Technology House of Representatives One Hundred Thirteenth Congress First Session" (PDF). United States Congress. p. 147. Retrieved 14 September 2019.
20. ^ "The Gran Telescopio Canarias (GTC) obtains the visible spectrum of C/2019 Q4 (Borisov), the first confirmed interstellar comet". Instituto Astrofisico de Canarias. Retrieved 2019-09-14.