Aqueously altered igneous rocks sampled on the floor of Jezero crater, Mars

The Perseverance rover landed in Jezero crater, Mars, to investigate ancient lake and river deposits. We report observations of the crater floor, below the crater's sedimentary delta, finding the floor consists of igneous rocks altered by water. The lowest exposed unit, informally named Séítah, is a coarsely crystalline olivine-rich rock, which accumulated at the base of a magma body. Fe-Mg carbonates along grain boundaries indicate reactions with CO₂-rich water, under water-poor conditions. Overlying Séítah is a unit informally named Máaz, which we interpret as lava flows or the chemical complement to Séítah in a layered igneous body. Voids in these rocks contain sulfates and perchlorates, likely introduced by later near-surface brine evaporation. Core samples of these rocks were stored aboard Perseverance for potential return to Earth.

An olivine cumulate outcrop on the floor of Jezero crater, Mars

The geological units on the floor of Jezero crater, Mars, are part of a wider regional stratigraphy of olivine-rich rocks, which extends well beyond the crater. We investigate the petrology of olivine and carbonate-bearing rocks of the Séítah formation in the floor of Jezero. Using multispectral images and x-ray fluorescence data, acquired by the Perseverance rover, we performed a petrographic analysis of the Bastide and Brac outcrops within this unit. We find that these outcrops are composed of igneous rock, moderately altered by aqueous fluid. The igneous rocks are mainly made of coarse-grained olivine, similar to some Martian meteorites. We interpret them as an olivine cumulate, formed by settling and enrichment of olivine through multi-stage cooling of a thick magma body.

Thermoelastic Response of the Juno Spacecraft's Solar Array/Magnetometer Boom and Its Applicability to Improved Magnetic Field Investigation

Juno was inserted into a polar orbit about Jupiter on 4 July 2016. Juno's magnetic field investigation acquires vector measurements of the Jovian magnetic field using a pair of a triaxial Fluxgate Magnetometers (FGMs) colocated with four attitude-sensing star cameras on an optical bench. The optical bench is placed on a boom at the outer extremity of one of Juno's three solar arrays. The Magnetic Field investigation (MAG) uses measurements of the optical bench inertial attitude provided by the micro-Advanced Stellar Compass (μASC) to render accurate vector measurements of the planetary magnetic field. During periJoves, orientation of the MAG Optical Benches (MOB) is determined using the spacecraft (SC) attitude combined with transformations between SC and MOB coordinate frames. Substantial prelaunch effort was expended to maximize the thermomechanical stability of the Juno solar arrays and MAG boom. Nevertheless, the Juno flight experience demonstrates that the transformation between SC and MAG reference frames varies significantly in response to spacecraft thermal excursions associated with large attitude maneuvers and proximate encounters with Jupiter. This response is monitored by comparing attitudes provided by the MAG investigation's four Camera Head Units (CHUs) with those provided by the Stellar Reference Unit (SRU). These systematic variations in relative orientation are thought to be caused by the thermoelastic flexure of the Juno solar array in response to temperature excursions associated with maneuvers and heating during close passages of Jupiter. In this paper, we investigate these thermal effects and propose a model for compensation of the MAG boom flexure.