# Radar sounding of Lucus Planum, Mars, by MARSIS

## TL;DR

This study uses MARSIS radar data to investigate the internal structure of Lucus Planum on Mars, supporting its pyroclastic origin and providing insights into its dielectric properties and subsurface composition.

## Contribution

The paper presents the first detailed radar analysis of Lucus Planum's internal structure, supporting its pyroclastic origin and characterizing its dielectric properties.

## Key findings

- Subsurface reflections found in three areas with distinctive surface morphology.
- East Lucus Planum's properties support a pyroclastic material hypothesis.
- Central Lucus Planum appears to be made of radar-attenuating material.

## Abstract

Lucus Planum, extending for a radius of approximately 500 km around 181{\deg} E, 5{\deg} S, is part of the Medusae Fossae Formation (MFF), a set of several discontinuous deposits of fine-grained, friable material straddling across the Martian highland-lowland boundary. The MFF has been variously hypothesized to consist of pyroclastic flows, pyroclastic airfall, paleopolar deposits, or atmospherically-deposited icy dust driven by climate cycles. MARSIS, a low-frequency subsurface-sounding radar carried by ESA's Mars Express, acquired 238 radar swaths across Lucus Planum, providing sufficient coverage for the study of its internal structure and dielectric properties. Subsurface reflections were found only in three areas, marked by a distinctive surface morphology, while the central part of Lucus Planum appears to be made of radar-attenuating material preventing the detection of basal echoes. The bulk dielectric properties of these areas were estimated and compared with those of volcanic rocks and ice-dust mixtures. Previous interpretations that east Lucus Planum and the deposits on the north-western flanks of Apollinaris Patera consist of high-porosity pyroclastic material are strongly supported by the new results. The north-western part of Lucus Planum is likely to be much less porous, although interpretations about the nature of the subsurface materials are not conclusive. The exact origin of the deposits cannot be constrained by radar data alone, but our results for east Lucus Planum are consistent with an overall pyroclastic origin, likely linked to Tharsis Hesperian and Amazonian activity.