Upper crustal stratigraphy beneath the InSight lander on Mars and implications for its formation
On November 2018, InSight landed at 4.502°N/135.623°E on the NW floor of ~27m-in-diameter Homestead hollow in the western Elysium Planitia, composed of ~60m thick, Early Amazonian degraded lava floods overlapping >500m thick Late Hesperian layered magmatic material. Around the lander, the landscape appeared as a relatively flat rock-strewn cratered plain with dunes far away. After the dust cleaning by retrorockets during the landing, the interior of the hollow, bounded by a gently darker slope,
... showed a surface covered by a clastic material, ranging from cobbles to sand, dominated by sand without aeolian bedforms. A majority of rocks showing a dark, aphanitic texture with a probable volcanic composition are interpreted to be impact ejected rocks due to their random spatial distribution, with a greater number of rocks in the western side of hollow. Thanks to pits formed by retrorockets and HP3 mole penetration, the stratigraphy of hollow could be investigated, showing a meter-scale long, ~10 cm thick lens-shaped interlayered deposits, with a pebble lens underneath the lander and a sandy lens at HP3 location, composed of multi-layered very fine sand mixed locally to coarse sand and granules poorly sorted, suggesting that the fine-grained material has been deposited and homogenized by wind transport. Although this material shows a weak cohesion near HP3 after hammering tests, it would not be cemented by aqueous fluids. The ~3 m thick surficial unit would be composed of superimposition of lens-shaped deposits mixing ejected rocks and finer aeolian clasts, overlying the fractured Early Amazonian volcanic bedrock.