We present LunarLeaper, a robotic explorer concept in response to the ESA 2023 Small Missions call. Pits, volcanic collapse features with near-vertical walls, have been identified across the lunar and Martian surface. These pits are high priority exploration destinations because some, referred to as skylights, might provide access to subsurface lava tube systems. Lava tubes are of particular interest for future human exploration as they offer protection from harmful radiation, micrometeorites and provide temperate and more stable thermal environments compared to the lunar surface. We propose to use a small legged robot (ETH SpaceHopper, <10 kg, 12U), to access and investigate the pit edge, using its ability to access complex and steep terrain more safely than a wheeled rover. LunarLeaper will be deployed in Marius Hills near the pit and traverse across the lateral extent of the hypothesized subsurface lava tube. On its traverse it will take measurements with a ground penetrating radar and a gravimeter, measurements that will allow us to survey the subsurface structure and detect and map lava tube geometry if present. The robot will approach the pit edges and acquire high resolution images of the pit walls containing uniquely exposed layers of the lava flows and regolith layers. These images will allow not only scientific advances of lunar volcanism and regolith formation, but also enable assessment of the stability of the pit structure and its use as a possible lunar base. The mission is expected to last 1 lunar day. The robot could be delivered to the surface by a small lander, as they are currently developed and planned by various national and commercial agencies and hop off the landing platform without the need for a robotic arm. It is highly flexible in accommodation and can thus make full use of the new international lunar ecosystem.

Mars is the first planet on which earthquakes (“marsquakes”) were observed in situ and clearly connected to active tectonic units on the surface^1-3. Mars shows no traces of plate tectonics, so pre-InSight the dominant tectonic process was assumed to be secular cooling and thus contraction of the lithosphere. Geological mapping of the surface had indicated many traces of recent volcanic activity and significant parts are covered by volcanic units⁴. The InSight seismic dataset localizes more than half of the observed seismic activity in Cerberus Fossae², a young (<10 Ma⁵) graben structure in Elysium Planitia, previously interpreted as a result of dyke intrusion⁶ or large-scale tectonic stress⁵. Spectral analysis of marsquakes observed in this region show a warm, elastically weakened source region⁷, e.g. due to partial melting at lithospheric depths⁸ or deformation due to a mantle plume⁹. The significant contribution of this small region to Mars’ global seismic budget means that volcanism shapes the planet’s surface at a higher rate than contraction. We discuss the mechanisms of Martian seismicity as they are currently understood and their relation to orbitally observed tectonics. References: ¹W. B. Banerdt et al., Nat. Geosci. 13, 183–189 (2020). ²D. Giardini et al., Nat. Geosci. 13, 205–212 (2020). ³P. Lognonné et al., Nat. Geosci. 13, 213–220 (2020). ⁴K. L. Tanaka et al., US Geol. Surv. Geol. Investig., 3292–3292 (2014). ⁵J. Vetterlein, G. P. Roberts, J. Struct. Geol. 32, 394–406 (2010). ⁶R. Ernst et al., Annu. Rev. Earth Planet. Sci. 29, 489–534 (2001). ⁷S. C. Stähler et al., Nat. Astron. 6, 1376–1386 (2022). ⁸A.-C. Plesa et al., in Advances in Geophysics, vol. 63, pp. 179–230 (2022). ⁹A. Broquet, J. C. Andrews-Hanna, Nat. Astron., 1–10 (2022).

During its over four years of Mars surface operations, NASA's InSight mission has seismically detected eight meteoroid impact events associated with craters identified in orbital images, ranging from a few meters to 150 meters in diameter. However, these events were either at epicentral distances closer than 5 degrees (~300 km), localized through seismo-acoustic signals, or further than 60 degrees (~3500 km). It is unlikely that seismically detectable impacts have not occurred at intermediate distances, but until now it has not been possible to associate a seismic event with craters that have been observed to form during the mission. We can now report the identification of a seismic signature associated with an impact crater >10 m in diameter confirmed by orbital imaging. Using the event azimuth determined from the S-wave arrival, we associate a new crater with formation dates consistent with this event. The seismic signal also indicates the presence of candidate surface waves, as seen for two other confirmed teleseismic impact events and some nearby impacts. The intermediate size and distance of this event serves as a crucial anchor point, bridging the gap between recent nearby and distant impacts. This event re-calibrates earlier estimates of Very-High Frequency (VF) event locations, redefining the search area to identify other seismic events associated with impacts formed within InSight's lifetime. The event also presents a rare opportunity to study differences in seismic wave behavior between events with shallow and deeper sources, facilitating comparisons in source geometry and dynamics. The acquired data not only enhances understanding of the local geological context but also establishes a crucial reference point for exploring seismic wave propagation in intermediate epicentral distances, paving the way for comprehensive planetary seismology studies.