Rock size‐frequency distributions on Mars and implications for Mars Exploration Rover landing safety and operations

Abstract

[1] The cumulative fractional area covered by rocks versus diameter measured at the Pathfinder site was predicted by a rock distribution model that follows simple exponential functions that approach the total measured rock abundance (19%), with a steep decrease in rocks with increasing diameter. The distribution of rocks >1.5 m diameter visible in rare boulder fields also follows this steep decrease with increasing diameter. The effective thermal inertia of rock populations calculated from a simple empirical model of the effective inertia of rocks versus diameter shows that most natural rock populations have cumulative effective thermal inertias of 1700-2100 J m À2 s À0.5 K À1 and are consistent with the model rock distributions applied to total rock abundance estimates. The Mars Exploration Rover (MER) airbags have been successfully tested against extreme rock distributions with a higher percentage of potentially hazardous triangular buried rocks than observed at the Pathfinder and Viking landing sites. The probability of the lander impacting a >1 m diameter rock in the first 2 bounces is <3% and <5% for the Meridiani and Gusev landing sites, respectively, and is <0.14% and <0.03% for rocks >1.5 m and >2 m diameter, respectively. Finally, the model rock size-frequency distributions indicate that rocks >0.1 m and >0.3 m in diameter, large enough to place contact sensor instruments against and abrade, respectively, should be plentiful within a single sol's drive at the Meridiani and Gusev landing sites.

Selection of the InSight Landing Site

“…The lander is tolerant of rocks up to 45 cm high underneath a footpad, rocks up to 45 cm high underneath the lander bottom deck, and rocks up to 55 cm high underneath the deployed solar arrays and 10 cm less in all cases if excess energy is absorbed by crushable material inside the lander legs. If the rock sizefrequency distribution (SFD) is similar to models based on measured distributions at existing landing sites (e.g., Golombek and Rapp 1997;Golombek et al 2003bGolombek et al , 2008bGolombek et al , 2012b, then this translates to an overall rock-induced failure rate of ∼0.35 % in regions with a 5 % cumulative fractional area (CFA) and a failure rate of ∼2.5 % in regions with a 10 % CFA.…”

“…Results indicated that for the landing constraint of 10 % rock abundance, there should be multiple SEIS/WTS (3)(4)(5)(6)(7)(8)(9)(10)(11) and HP 3 (6-15) deployment sites that are free from 6 cm diameter (3 cm high) rocks. The second technique used Poisson statistics to evaluate the probability that a rock of a given diameter or larger would be present in a single random sample of a given area for a given rock abundance, which has been used to evaluate the probability of failure for landing MER, PHX and MSL in observed and modeled rock abundances (Golombek et al 2003b(Golombek et al , 2008b(Golombek et al , 2012b. The placement probabilities were determined for multiple discrete placement options for each instrument and WTS in the workspace and then made conditional on finding locations that are free from rocks >6 cm diameter for both instruments for a 10 % model rock abundance.…”

Thermal Tomography of Asteroid Surface Structure

“…5 for bulk density values of ρ = 1000 and 3000 kg m -3 , assuming c = 680 J kg -1 K -1 (Chesley et al 2003;Čapek, & Vokrouhlický, 2004); the density would be expected to increase with depth from the lower value, which is representative of porous surface material. Superimposed on the plot of , Golombek et al 2003 and references therein, for Martian rocks with diameter > 20 cm) are reached some tens of centimeters to meters below the surface in the case of the MBAs (the median diameter in our dataset = 24 km). In the case of the much smaller (km-sized) NEOs our results indicate that the porous surface layer is thinner, and suggest that large pieces of solid rock exist just a meter or less below the surface.…”

Thermal Infrared Imaging Experiments of C-Type Asteroid 162173 Ryugu on Hayabusa2

“…Thermal inertia maps are often used to estimate rock or boulder populations (Golombek et al 2003). Prior to the descent and touchdown operation, it is important to assess whether the surface thermal environment and boulder distribution is hazardous for landing or not.…”