Rotationally Resolved Spectroscopy of (93) Minerva with the Lowell Discovery Telescope + Near-Infrared High Throughput Spectrograph: more evidence for widespread primitive materials

We present new rotationally resolved observations of asteroid (93) Minerva with the Lowell Discovery Telescope, investigating potential heterogeneity of Minerva’s surface mineralogy. McAdam et al., (2018, Icarus, 306, pp.32-49) identify the presence of amorphous materials on the surface of Minerva from an IRTF+SPeX spectrum taken in 2003. Marchis et al., (2013 Icarus, 224(1), pp.178-191) also observed Minerva with SPeX but did not identify such a feature. Minerva’s spectrum had a significant red slope in the Marchis observations. These observations were taken at 87% difference in rotation phase. This suggests that there is surface heterogeneity on Minerva. We collected near-infrared spectra of (93) Minerva on NIHTS using the 1.34×12” slit covering the wavelength range from 0.86-2.46 microns. Results: Using LDT+NIHTS, we observed ~55% of Minerva’s surface with some overlap with previous IRTF+SpeX observations. We find that (93) Minerva shows evidence for widespread amorphous materials, similar to the least-processed meteorites presented in McAdam et al., 2018. Implications: The implications of these results are that (1) the surface of Minerva, that we observed, appears to have abundant amorphous materials, (2) these materials seem to be wide-spread, appearing in all the usable data, spanning at least 30-40% of the surface, (3) more data are needed to determine if Minerva has a homogeneous or heterogeneous surface. With future observations we can potentially constrain the timing of accretion of this asteroid.