Work

Infrared-to-visible albedo ratio of Phobos

Year: 2026

Type: article

Abstract: Aims . The ratio between infrared and visible albedo, p IR / p V , provides a simple proxy for the spectral slope of asteroid surfaces between the visible and near-infrared wavelength ranges. The aim of this work is to assess whether the different spectral units of Phobos occupy the same spectral parameter space as primitive asteroid populations in order to confirm, or not, its possible asteroidal origin. Methods . For each of the three spectral units of Phobos (red, transitional, and blue), we extracted averaged, normalised reflectance spectra by comparing normalised reflectance in the visible (0.50–0.60 m) and near-infrared (3.1–3.8 m) wavelength ranges from the Mars Express OMEGA instrument to compute a proxy for the infrared-visible albedo ratio ( R P ). Then, using the database of visible and infrared albedos compiled in the Minor Planet Physical Properties Catalogue (MP3C), we computed asteroid p IR / p V values ( R A ) for comparison with those of Phobos. Results . The R P values for the red, transitional, and blue regions vary between 2.90 and 3.12, 2.32 and 2.35, 1.64 and 1.85, respectively. These values span a range occupied by primitive asteroid populations, with the transitional and red regions coinciding with the high ratio regime within the p IR / p V domain, commonly associated with red-sloped primitive asteroids, including D- and T-type objects as well as Jupiter trojans.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202661534