Nine samples, consisting of four pairs of rock cores and a tube of atmospheric gas, were collected from the floor of Jezero Crater, Mars.• In situ observations of crater floor outcrops, used as proxies for the samples, reveal aqueously altered igneous lithologies.• Perseverance will leave one sample from each pair at the Three Forks depot and retain a second to be cached with future samples.

Motivated by recent evidence for subduction in Europa's ice shell, we explore the geophysical feasibility of this process. Here we construct a simple model to track the evolution of porosity and temperature within a slab that is forced to subduct. We also vary the initial salt content in Europa's ice shell and determine the buoyancy of our simulated subducting slab. We find that porosity and salt content play a dominant role in determining whether the slab is nonbuoyant and subduction in Europa's ice shell is actually possible. Generally, we find that initially low porosities and high salt contents within the conductive lid are more conducive to subduction. If salt contents are laterally homogenous, and Europa has a reasonable surface porosity of ϕ0 = 0.1, the conductive portion of Europa's shell must have salt contents exceeding ~22% for subduction to occur. However, if salt contents are laterally heterogeneous, with salt contents varying by a few percent, subduction may occur for a surface porosity of ϕ0 = 0.1 and overall salt contents of ~5%. Thus, we argue that under plausible conditions, subduction in Europa's ice shell is possible. Moreover, assuming that subduction is actively occurring or has occurred in Europa's recent past provides important constraints on the structure and composition of the ice shell.

The presence and distribution of preserved organic matter on the surface of Mars can provide key information about the Martian carbon cycle and the potential of the planet to host life throughout its history. Several types of organic molecules have been previously detected in Martian meteorites1 and at Gale crater, Mars2–4. Evaluating the diversity and detectability of organic matter elsewhere on Mars is important for understanding the extent and diversity of Martian surface processes and the potential availability of carbon sources1,5,6. Here we report the detection of Raman and fluorescence spectra consistent with several species of aromatic organic molecules in the Máaz and Séítah formations within the Crater Floor sequences of Jezero crater, Mars. We report specific fluorescence-mineral associations consistent with many classes of organic molecules occurring in different spatial patterns within these compositionally distinct formations, potentially indicating different fates of carbon across environments. Our findings suggest there may be a diversity of aromatic molecules prevalent on the Martian surface, and these materials persist despite exposure to surface conditions. These potential organic molecules are largely found within minerals linked to aqueous processes, indicating that these processes may have had a key role in organic synthesis, transport or preservation.

Several mineralogically diverse regions across Mars are capped by dark‐toned rock formations emplaced during the Noachian‐Hesperian transition, an era encompassing a shift in volcanism from dominantly explosive to effusive. However, these caprocks' origins are uncertain, limiting insight into the nature of this shift. We explore the potential volcanic ash origin of a widespread (∼50,000 km2) mafic caprock in the Circum‐Isidis region via an integrated photogeologic and remote‐compositional analysis. We also investigate whether this unit is genetically equivalent to a mafic rock formation exposed in the floor of Jezero Crater. We find: (a) the Jezero Floor and Capping Units are morphologically, stratigraphically, and compositionally similar, suggesting a shared formation mechanism, and (b) the tonal layering and draping characteristics of the Capping Unit are most consistent with a volcanic ash origin atop the ultramafic Olivine‐Rich Unit, also an ash. Our hypotheses can be tested by the Perseverance rover and studies of returned samples.