Spectroscopic investigation of the large Potentially Hazardous Asteroid (52768) 1998OR2 within NEOROCKS EU project

With an estimated diameter of about 2200m (http://neo.ssa.esa.int/), and a MOID (minimum orbital intersection distance) of 0.0154 au (6 Lunar Distances LD), (52768) 1998 OR2 is one of the largest known Potentially Hazardous Asteroid. On 29 April 2020 at 09:56 UTC 1998 OR2 had a very close passage to Earth at a distance of 0.042 au (16 LD). Close approaches by large asteroids like 1998 OR2 are a quite rare event.

This asteroid has a highly eccentric orbit (e=0.57) with minor perturbations: this causes it to swap continuously. Moreover it is classified as Amor or Apollo asteroid  depending on the orbital phase.

Within the NEOROCKS EU project (“The NEO Rapid Observation, Characterization and Key Simulations” - SU-SPACE-23-SEC-2019 from the Horizon 2020) - WP3-Task3.2 (Reflectance Spectroscopy) we observed 1998OR2 through the 120 cm “Galileo” telescope in Asiago using Boller & Chivens spectrograph instrument on 15 April 2020 when it was at 1.01 au heliocentric distance and 0.078 au distance from Earth.

 1998 OR2, discovered on 24 July 1998 by NEAT program, is a fast rotator in the NEO population with a rotational period of 4.11 h  (Koehn et al, 2014; Skiff et al., 2019, and Warner and Stephens, 2020) and shows a large crater-like concavity through radar images (Virkki, A. K. 2020).

Due to its rapid rotation, we were able to monitor the reflectance spectroscopy of 1998 OR2 for one nearly complete rotation during the night of 15 April 2020. We acquired 11 spectra, one every 20 minutes, spanning from 19:22 to 23.26 UTC. This allowed to investigate the possible variegation of the object across its surface and potentially connected with its big crater.

It is unlikely that one of these large asteroids  could  impact the Earth over the next century, in fact also this asteroid poses no possibility of impact for at least the next 200 years, even if in its next close approach to Earth in 2079,  it will pass by close ,  about four times the lunar distance. It is however extremely important to keep these objects monitored and to investigate their physical and compositional properties to implement mitigation techniques.

In this work we will present optical spectroscopic characterization of 1998 OR2 and the comparison of the taxonomic classification resulting from these spectra with the Xk obtained by Binzel et al. (2019). Additionally we will investigate its possible surface variegation according to the geometry of observation and the asteroid shape.

Acknowledgement: This work has been performed within grant agreement No 870403 (project NEOROCKS) funded by the European Union’s Horizon 2020 research and innovation programme.

References

Koehn, Bruce W.; Bowell, Edward G.; Skiff, Brian A.; Sanborn, Jason J.; McLelland, Kyle P.; Pravec, Petr; et al. (October 2014). "Lowell Observatory Near-Earth Asteroid Photometric Survey (NEAPS) - 2009 January through 2009 June". The Minor Planet Bulletin. 41 (4): 286–300

Virkki, A. K. (23/04/2020) Planetary Radar Science Group. NAIC-Arecibo Observatory (http://www.naic.edu/~pradar/press/1998OR2.php)

R.P.Binzel, F.E.DeMeo, E.V.Turtelboom, S.J.Bus, A.Tokunaga, T.H.Burbine, C.Lantz, D.Polishook, B.Carry, A.Morbidelli, M.Birlan, P.Vernazza, B.J.Burt, N.Moskovitz, S.M.Slivan, C.A.Thomas, A.S.Rivkin, M.D.Hicks, T.Dunn, V.Reddy, J.A.Sanchez, M.Granvik, T.Kohout, 2019, Compositional distributions and evolutionary processes for the near-Earth object population: Results from the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS), Icarus, 324, 41.

Warner, Brian D., Stephens, Robert D., Near-Earth Asteroid Lightcurve Analysis at the Center for Solar System Studies: 2019 December - 2020 April, 2020,  The Minor Planet Bulletin (ISSN 1052-8091). Bulletin of the Minor Planets Section of the Association of Lunar and Planetary Observers, Vol. 47, No. 3, pp. 200-213.

Brian A. Skiff, Kyle P. McLelland, Jason J. Sanborn, Petr Pravec, Bruce W. Koehn, 2019,  Lowell observatory near-earth asteroid photometric survey (NEAPS): paper 4, Minor Planet Bulletin 46.