Observations of Phobos and Deimos with SpeX at NASA infrared telescope facility

We measured near-infrared (NIR) reflectance spectra of Phobos and Deimos, using the prism (0.7-2.52 mu m) and long-wavelength cross dispersed (LXD: 1.9-4.2 mu m) modes of NASA Infrared Telescope Facility (IRTF)'s SpeX instrument. The goal of this study is to investigate the surface composition of Phobos and Deimos and search for any mineralogical absorption signatures that may be present on their surfaces, especially in the LXD spectral range. Prism spectra of Phobos showed significant slope variation at shorter wavelengths (lambda < 1.3 mu m), which indicates surface heterogeneity possibly due to regolith's composition and grain size, and/or space weathering. Deimos' prism spectra were found to be consistent with the more red-sloped prism spectra of Phobos. The measured LXD spectra of Deimos revealed evidence of hydration with 3-mu m band depths at 2.90 mu m of 4-5%. The 3-mu m band in Deimos could be attributed to exogenic sources such as solar wind implantation or OH-bearing impactors, or to an endogenic source and the presence of carbonaceous material on its surface. Phobos' and Deimos' prism and LXD spectra, however, show no indications for absorption signatures of mafic silicates (i.e., pyroxene, olivine), organics nor carbonates.

Automated summary

By measuring the near-infrared reflectance spectra of Phobos and Deimos, this study aims to investigate their surface composition and mineralogical absorption signatures. Evidence of hydration was found in Deimos' LXD spectra, possibly attributed to exogenic or endogenic sources. However, no absorption signatures of mafic silicates, organics, or carbonates were observed in the prism and LXD spectra of Phobos and Deimos.