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Located on the slopes of Jezero Crater, the Broom Point site has intrigued scientists since its orbital detection. Recent analyses reveal microscopic structures whose origin could challenge our understanding of Martian history.
This image from NASA's Perseverance Mars rover, a processed RMI (Remote Micro Imager) mosaic from SuperCam, shows part of the "St. Pauls Bay" target, acquired from the lower part of Witch Hazel Hill on the rim of Jezero Crater.
The image reveals hundreds of strange spherical objects composing the rock. Perseverance captured this image on March 11, 2025, the 1442nd Martian day of the Mars 2020 mission.
Image NASA/JPL-Caltech/LANL/CNES/IRAP.
A discovery with multiple mysteries
The rock named "St. Pauls Bay" features millimeter-sized spherules of varying shapes—some perfectly round, others oblong or fragmented. Their surfaces show textures with micro-cavities and striations that could reveal their formation process. These unusual characteristics clearly distinguish these structures from previously documented Martian concretions.
The arrangement of spherules in the rock matrix suggests multiple phases of geological development. Their random distribution contrasts with the typical alignments of sedimentary deposits, ruling out a purely stratigraphic origin. The rover's instruments have detected compositional variations between the spherules and their immediate surroundings, adding another layer of intrigue.
This discovery reignites the debate about the diversity of Martian geological processes. Scientists are now considering scenarios combining hydrological action, meteorite impacts, and secondary volcanic activity. Solving this mystery may require more advanced in-situ analyses or sample returns to Earth.
Three scenarios for a controversial origin
The first hypothesis involves formation by ancient water circulation. These spherules could have formed through concretion—a process where dissolved minerals gradually accumulate around a core, creating concentric spherical structures, as observed in some terrestrial sedimentary rocks. Their random distribution and polymorphism would suggest varying chemical conditions over time. However, certain features like micro-cavities remain difficult to explain by this mechanism alone.
NASA's Perseverance Mars rover captured this image of the "St. Pauls Bay" target (the dark floating block at the right of the view) using its Left Mastcam-Z, one of two cameras mounted high on the rover's remote sensing mast. Perseverance acquired this image on March 13, 2025, the 1444th Martian day of the Mars 2020 mission.
NASA/JPL-Caltech/ASU
A volcanic scenario is also considered, where these structures could correspond to lava droplets ejected during explosive eruptions. This origin would explain the perfectly spherical shapes and certain unique surface textures. Similar phenomena are documented in terrestrial volcanic regions, with basaltic lapilli. However, the isolated location of these spherules raises questions in this interpretive framework.
Finally, an impact-related genesis is proposed. The spherules could be condensates of vaporized rock from a cosmic collision or fragments of ejected material. This model would account for the angular shapes and some atypical mineral inclusions. The environment of Jezero Crater, itself formed by an impact, lends credibility to this hypothesis, though more direct evidence is still lacking.