21-EPN-FT1-030: Laboratory simulation of the Martian surface brightness temperature response to Phobos eclipses
Visit by Nils Mueller of Freie Universität Berlin (Germany) and Joerg Knollenberg of DLR (Germany) to TA2 Facility 25 – Swedish Planetary Ices Laboratory.
Dates of visit: 10-19 April 2024
Report Summary: The objective of this series of experiments was to support the data interpretation of short changes in insolation of planetary bodies as they happen during solar eclipses or transits. The temperature response of Martian regolith to the transit of Phobos has been observed by NASA’s InSight mission and interpreted in terms of layering in the near-surface. The Planetary Ices Laboratory is capable of simulating such events on Earth using a thermal vacuum chamber that is tolerant to dust and a solar simulator. The chamber was evacuted, either refilled with 5.5 mbar CO2 or left at <1e-4 mbar (simulating Mars and space, respectively), cooled below -60 °C, then the contained regolith analogue material was illuminated until the temperature approached an equilibrium.
During our time in the planetary ices lab we conducted tests with different materials configurations. The first consists of 2-4 mm Mojave Mars Simulant (MMS) filling the tray to a depth of 2 cm. The second adds 2 or 3 monolayers of <100 μm MMS. The third extends the dust layer to approximately 3 mm. The fourth adds cm sized clasts to recreate a typical planetary scene. The eclipses consisted of closing the shutter of the solar simulator for various durations. The corresponding temperature response of the material extends to different depths an therefore may sense different layers. The surface temperature was measured using a radiometer comparable to those on past Mars and future Phobos missions.
