Mueller N, Piqueux S, Lemmon M, Maki J, Lorenz RD, Grott M, Spohn T, Smrekar SE, Knollenberg J, Hudson TL, Krause C, Millour E, Forget F, Golombek M & Attree N (2021) Near Surface Properties of Martian Regolith Derived From InSight HP3-RAD Temperature Observations During Phobos Transits. Geophysical Research Letters, 48 (15), Art. No.: e2021GL093542. https://doi.org/10.1029/2021GL093542
The Mars moon Phobos passed in front of the Sun from the perspective of the InSight lander on several occasions. The Mars surface temperatures measured by the lander became slightly colder during these transits due to the lower amount of sunlight the surface received at this time. The transits only last 20–35 s and therefore only the very top layer, about 0.3–0.8 mm, of the ground has time to cool significantly. The top layer cools and heats up faster than we expected based on the temperature changes of the day-night cycle, which affects about 4 cm of the ground. Based on this observation we conclude that the material in the top mm of the ground is different from that below. A possible explanation would be an increase of density with depth, a larger fraction of smaller particles such as dust at the top, or a layer where particles are slightly cemented together beginning at 0.2–4 mm below the surface.
phobos transit; thermal inertia; thermal conductivity
Additional co-authors: Axel Hagermann, Matthew Siegler, and W Bruce Banerdt
Geophysical Research Letters: Volume 48, Issue 15