An assessment of the meteoritic contribution to the Martian soil

Abstract

The addition of meteoritic material to the Mars soils should perturb their chemical compositions, as has been detected for soils on the Moon [Anders et al., 1973] and sediments on Earth [Kyte and Wasson, 1986]. Using the measured mass influx at Earth and estimates of the Mars/Earth flux ratio, we estimate the continuous, planet‐wide meteoritic mass influx on Mars to be between 2700 and 59,000 t/yr. If distributed uniformly into a soil with a mean planetary production rate of 1 m/b.y., consistent with radar estimates of the soil depth overlaying a bouldered terrain in the Tharsis region [Christensen, 1986], our estimated mass influx would produce a meteoritic concentration in the Mars soil ranging from 2 to 29% by mass. Analysis of the Viking X ray fluorescence data indicates that the Mars soil composition is inconsistent with typical basaltic rock fragments but can be fit by a mixture of 60% basaltic rock fragments and 40% meteoritic material [Clark and Baird, 1979]. The meteoritic influx we calculate is sufficient to provide most or all of the material required by the Clark and Baird [1979] model. Particles in the mass range from 10−7 to 10−3 g, about 60–200 μm in diameter, contribute 80% of the total mass flux of meteoritic material in the 10−13 to 10 6 g mass range at Earth [Hughes, 1978]. On Earth atmospheric entry all but the smallest particles (generally ≤ 50 μm in diameter) in the 10−7 to 10−3 g mass range are heated sufficiently to melt or vaporize. Mars, because of its lower escape velocity and larger atmospheric scale height, is a much more favorable site for unmelted survival of micrometeorites on atmospheric deceleration. We calculate that a significant fraction of particles throughout the 60–1200 μm diameter range will survive Mars atmospheric entry unmelted. Thus returned Mars soils may offer a resource for sampling micrometeorites in a size range which is not collectable in unaltered form at Earth.