Vishnu Reddy, University of Arizona; Adam Battle, University of Arizona; Tanner Campbell, University of Arizona; Paul Chodas, Jet Propulsion Laboratory; Al Conrad, University of Arizona; Dan Engelhart, University of New Mexico; James Frith, AFRL Space Vehicles Directorate; Roberto Furfaro, University of Arizona; Davide Farnocchia, Jet Propulsion Laboratory; Ryan Hoffmann, AFRL Space Vehicles Directorate; Olga Kuhn, University of Arizona; David Monet, AFRL Space Vehicles Directorate; Neil Pearson, Planetary Science Institute; Elena Plis, AFRL and Georgia Tech; Jacqueline Reyes, The University of Texas at El Paso; Barry Rothberg, LBTO; Benjamin Sharkey, University of Arizona; Juan Sanchez, Planetary Science Institute; Christian Veillet, University of Arizona; Richard Wainscoat, University of Hawaii
Keywords: Near-IR Spectroscopy, Planetary Defense, Cis-Lunar SSA, XDA
Abstract:
2020 SO was discovered by the Pan-STARRS survey on September 17, 2020. Originally classified as a near-Earth object, the object’s artificial nature became evident due to its low velocity relative to Earth and changes to its orbit about the Sun. 2020 SO is thought to be a Centaur rocket body (R/B) from the launch of the Surveyor 2 mission to the Moon based on a backward propagation of its orbit. We characterized 2020 SO using a range of ground-based optical and near-infrared telescopes to constrain its true nature. Due to the relative faintness of the target (V~21.5), initial characterization observations following its discovery were made with the twin 8.4-meter Large Binocular Telescope (LBT). We obtained Sloan (g’r’i’z’) broadband colors of 2020 SO using the Large Binocular Camera to constrain its rotational properties and visible spectral slope. The color ‘spectrum’ shows a red spectral slope distinct from those of S- and C-type asteroids. We compared the color spectrum of 2020 SO with low resolution (R~30) visible wavelength (0.45-0.95 µm) spectra of two Centaur R/Bs (NORAD IDs 3598 and 6155) obtained using the RAPTORS 0.6-meter telescope. The two datasets are consistent with slight differences in spectra slope. 2020 SO is redder than the Centaur R/Bs. These spectral slope differences could be due to phase angle difference between the two observations, the different orbital environments to which they have been exposed, time on orbit, or differences of their physical characteristics. Diagnostic absorption bands in the near-infrared (0.75-2.5 µm) have traditionally been used to characterize surface properties of solid surfaces. The SpeX instrument on the NASA Infrared Telescope Facility (IRTF) was used to obtain a low-resolution (R~100) near-IR spectrum (0.70-2.5 µm) of 2020 SO. The object was observed on three dates as it moved closer to the Earth. The spectra show a general rise in reflectance in the range of ~0.70-1.63 µm and a neutral spectral slope beyond that. The visible colors obtained by the LBT are consistent with the near-IR data. Three spectrally dominant materials are identified on the Centaur R/B consistent with those used for the Surveyor 2 mission. These include: a stainless steel R/B body; white polyvinyl fluoride (PVF) which covered the aft bulkhead radiation shield; and aluminized mylar which insulated the forward bulkhead of the R/B. The red spectral slope between 0.69-1.63 µm is consistent with the spectrum of stainless steel. Also detected were three absorption features in the near-IR spectrum of 2020 SO centered at 1.43±0.02 µm, 1.72±0.01 µm, and 2.29±0.01 µm. The laboratory spectrum of pure PVF obtained by the USGS was used to verify its presence on 2020 SO. The PVF lab spectrum shows a sharp rise in reflectance ±0.02 µm, 1.71±0.01 µm, and 2.30±0.01 µm, consistent with those seen on 2020 SO. The lab spectra of aluminized mylar are still under investigation to look for affinities to 2020 SO. Our goal is to create a mixing model using these three spectrally significant components as a next step. As part of our final characterization efforts, we observed Centaur R/B (NORAD ID: 04882) with the NASA IRTF, which is broadly consistent with 2020 SO.
Date of Conference: September 14-17, 2021
Track: Non-Resolved Object Characterization