THE GEOMORPHIC EVOLUTION OF LAVA PLAINS AT THE INSIGHT AND SPIRIT LANDING SITES: COMPARISION OF CRATER RETENTION AGES AND MORPHOMETRY

The InSight mission landed in a ~27 meter-diameter (D) degraded crater, informally named Homestead hollow, on a Hesperian- to Early Amazonian-aged basaltic lava plain in Elysium Planitia. Nearly 15 years prior, the Mars Exploration Rover Spirit landed on Late Hesperian- to Amazonian-aged basaltic lava plains in Gusev crater. Along its traverse, Spirit investigated sediment-filled hollows that are comparable in size and appearance to Homestead hollow, yet many appear to retain better-preserved rims (e.g., less degraded).

Previous work using HiRISE images established a crater classification system and degradational continuum across the InSight landing ellipse covering an area of 21 km². The estimated crater degradation rates and rim erosion rates were based on 10-100 m-scale craters using morphometric parameters. Given the broad similarities between the Spirit and InSight landing sites, we use comparable datasets and methods to examine if the populations of degraded craters and quasi-circular depressions on the floor of Gusev follow the same degradation continuum as observed at the InSight landing site.

In the ~2,500 km² area encompassing the volcanic plains in the vicinity of the Spirit landing site, a preliminary population of all impact craters (D~0.2-1 km) using CTX images is consistent with the expected population production function, yielding an Early Amazonian age. This estimated absolute age of ~2.2 Ga is similar to the InSight landing site based on the size frequency distribution of craters for the same D range. In a detailed look at the 21 km² area around the Spirit landing site, we mapped 9,000+ craters using HiRISE data (D range: ~1.6 to 282 m). Preliminary results indicate morphologically distinct populations of craters are present on the Gusev plains, ranging from bowl shaped to degraded quasi-circular depressions. Morphometric characteristics for each crater (e.g., depth, rim height, rim and floor slope) within like classes were calculated and will be used to estimate degradation rates and rim erosion rates. Comparison between Gusev and Elysium will further our understanding of the degradation history of craters on Hesperian to Early Amazonian volcanic surfaces, and may provide clues about the timing and extent of burial and exhumation events they have experienced.