Soil Thermophysical Properties Near the InSight Lander Derived From 50 Sols of Radiometer Measurements.

Area of Science:

• Planetary Science
• Geophysics
• Remote Sensing

Background:

• The InSight lander's radiometer collected unique, high-cadence measurements of Martian soil thermophysical properties.
• Data was acquired in Homestead hollow, focusing on a surface minimally impacted by the lander and landing.
• Environmental data from other InSight instruments provided context for the soil analysis.

Purpose of the Study:

• To characterize the thermophysical properties of Martian soil using InSight lander data.
• To determine the soil's composition and layering based on temperature cycles.
• To compare ground-based measurements with pre-landing orbital data.

Main Methods:

• Analyzing diurnal temperature cycles from the InSight lander's radiometer.
• Fitting temperature data using a homogenous soil model to derive thermal inertia and albedo.
• Comparing ground-based thermal inertia results with orbital thermal infrared data.

Main Results:

• Martian soil exhibits a thermal inertia of 183 ± 25 J m⁻² K⁻¹ s⁻¹/² and an albedo of 0.16.
• This corresponds to very fine to fine sand, with most particles <140 μm.
• Analysis indicates thin near-surface layers (top few mm) and deeper layers (below ~4 cm) with distinct thermophysical properties.

Conclusions:

• The low thermal inertia suggests limited soil cementation in the upper layers (4-8 cm), with cement volumes <1%.
• This finding presents a challenge when reconciling with visible evidence of overhangs in Martian pits.
• Ground-based measurements provide a more detailed understanding of Martian soil properties than orbital data alone.