Did Mars Get an Isotopic Facelift?

Image credit: NASA/JPL-Caltech/UTA/UA/MSSS/ESA/DLR/JPL Solar System Visualization Project

Like Earth, Mars has a core, mantle, and crust, which separated due to density contrasts in a process known as differentiation. One anomalous feature of Mars is that its mantle is believed to contain high abundances of elements that like to bond and form compounds with iron. These siderophile (‘sidero-’ = iron, ‘-phile’ = loving) elements typically sequester themselves into the core of a planet early during its formation. Researchers have used this observation to propose that Mars experienced late-stage impact events that mixed additional siderophile elements into the mantle.

Scientists from the Southwest Research Institute and the University of Maryland completed a series of impact simulations designed to test how different collision scenarios affected the chemical and physical development of the martian mantle. Their simulation involved a large chondritic projectile colliding with Mars at a variety of angles and speeds, equivalent to the average adult being hit with a six-pound bowling ball. They concluded that up to three of these impacts could account for the estimated abundances of siderophile elements in the martian mantle. These results have implications for how scientists interpret martian history. For example, this study predicted that the impactors would not completely mix with the martian mantle, resulting in a heterogeneous distribution of isotopes. Some of these isotopes, like those of hafnium (Hf) and tungsten (W), are important because scientists use their abundances and signatures to hypothesize that Mars grew rapidly in a very young solar system in only 2 to 4 million years. However, if large collisions alter and potentially reset these isotopes, then Mars could have formed over a period as long as 20 million years. READ MORE