THE IMPORTANCE OF SAMPLES DELIVERED TO EARTH BY MARS SAMPLE RETURN FOR UNDERSTANDING THE MARTIAN MANTLE: A REPORT FROM THE IMOST TEAM

Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the iMOST team is to re-evaluate and update the sample-related science and engineering objectives of a Mars Sample Return (MSR) campaign. Here we will present a subset of these goals focusing on the importance of MSR to understanding the Martian interior.

The chemistry and mineralogy of the Martian interior is largely constrained by the type of samples we have of Mars – martian meteorites – with inputs from geophysics, surface rover analyses of igneous rocks, and orbital analyses of the crust. However, comparisons of martian meteorites and igneous rocks analyzed on the surface of Mars show that martian meteorites do not represent average martian crust or magmas. Young Martian meteorites and ancient igneous rocks analyzed in situ by rovers have different elemental compositions, suggesting different source regions – this could be confirmed by radiogenic isotope data and chronology on returned samples; these differences are attributable to a sampling bias inherent the process that delivered the meteorites to Earth. Therefore, a proposed iMOST objective would be to use samples of igneous rocks - either in place or transported - with a range of compositions and an emphasis on older (>3.5 Ga) ages, to help reconstruct the processes that have affected the origin and modification of the interior. Understanding the petrogenesis of igneous rocks sampled from well-documented locations from a well-constrained igneous unit would provide novel insights into the physical properties of martian magmas; the composition(s) of their mantle sources including major, trace, and volatile elements, noble gases, and isotopic characteristics; the conditions of magma genesis; the timing and duration of igneous activity; and subsequent modification by secondary processes.