MMT/Binospec spectroscopy of near earth object 2020 SO distinguishes it from common natural asteroids
ATel #14241; B. Weiner (MMT Observatory), E. Pearce, H. Krantz, A. Block (Steward Observatory), R. Howie, S. Kattner, S. Self, G. Williams (MMT Observatory)
on 3 Dec 2020; 01:46 UT
Credential Certification: Benjamin Weiner (bjw@mmto.org)
Subjects: Optical, Asteroid, Near-Earth Object
The near Earth object 2020 SO, discovered by Pan-STARRS1 in September 2020, has been temporarily captured into Earth orbit. P. Chodas (JPL) has suggested that it is an artificial object, possibly a Centaur rocket booster launched in 1966. On UT 2020 November 16, we observed 2020 SO with the Binospec spectrograph at the MMT Observatory with 20x1 minute exposures, covering 3700-8600 A at R=1300, and a solar analog G2V star for calibration. On UT 2020 November 20 and 21, we reobserved 2020 SO and the S-type asteroid (15) Eunomia with the same spectrograph, and G2V and standard stars.
Normalized by a G2V stellar spectrum, 2020 SO has a red slope of reflectance while Eunomia has a near-constant slope: logarithmic slopes of reflectance on wavelength of +0.8 vs. +0.1 dex/dex. In relative SDSS colors synthesized from the spectra, 2020 SO is redder than Eunomia by 0.18 mag in g-r and 0.17 mag in r-i (errors ~ 0.03 mag). These colors place it well to the red of the color-color distribution of S-type asteroids (Ivezic et al 2001), and of C-type asteroids, which are bluer than S-types.
The properties of 2020 SO are similar to 2010 KQ, a near Earth object also suggested to be a rocket booster stage, which exhibited red color versus an S-type asteroid, and orbit deviations suggestive of a high area/mass ratio (R. Miles, 2011, JBAA, 121, 350). The red colors of 2010 KQ were consistent with space weathered paint on NASA's LDEF (Miles 2011). We encourage further spectroscopy and photometry to measure the phase curve and orbit of 2020 SO during its close approach to Earth.
