Martian moon Deimos captured by the Thermal Infrared Imager (TIRI)
Martian moon Deimos captured by the Thermal Infrared Imager (TIRI)
Martian moon Deimos shines much brighter than the red planet beneath it in this Thermal Infrared Imager image acquired during the Hera mission's 12 March 2025 gravity-assist flyby of Mars. For visible light, the opposite is true: Deimos is much less reflective than the Martian surface.
Hera's TIRI – supplied to the mission by the Japan Aerospace Exploration Agency, JAXA – sees in mid-infrared spectral bands to chart surface temperature. Because Deimos lacks an atmosphere, the side of the moon being illuminated by the Sun is considerably warmer than the planet beneath it.
To the bottom right of the Martian disc, in blue, is the Hellas basin, among the largest known impact craters in the Solar System with a diameter of 2300 kilometres and a depth of more than seven kilometres – relatively cool at such a high southern latitude during this time of the Martian year.
By revealing surface temperature in this way, TIRI imaging serves to reveal physical properties such as roughness, particle size distribution and porosity.
