As Americans enjoy fireworks and the holidays on the Fourth of July, NASA's Perseverance Mars rover is detecting tiny, perfectly round spheres on Mars that may hold secrets to the planet's fiery past. Unlike the hematite "blueberries" discovered years ago, these newly discovered spheroids are of volcanic or impact origin, possibly formed during violent meteoroid impacts or ancient volcanic eruptions. Their unique composition offers scientists an opportunity to understand Mars' dynamic history—whether it was shaped by the fires of its interior or the violent impacts of the universe.

NASA's "Perseverance" Mars rover took this photo of chondrule-containing regolith in Mount Russell using the WATSON camera mounted on its arm at 12:46:29 local time on July 5, 2025 (the 1555th Martian day of the Mars 2020 mission). WATSON (Wide-angle Terrain Sensor for Operations and Engineering) is a close-range color camera used in conjunction with the rover's SHERLOC instrument (which uses Raman and fluorescence to scan the habitable environment to detect organics and chemicals); both are located on a turret at the end of the rover's robotic arm. Image source: NASA/JPL-Caltech

Mysterious Mars Sphere

It is rare for a Mars rover to find a nearly perfect sphere on the surface of Mars. More than two decades ago, NASA's Opportunity Mars rover made headlines when it discovered hematite-rich spheroids (nicknamed "blueberries") near its landing site on Meridiani Plateau. Now, the Mars Perseverance rover has discovered a similar surprise: small globular structures, some embedded in bedrock and others scattered across an area informally known as "Witch Hazel Mountain."

In a previous update, the team highlighted Perseverance's close study of a rock formation containing spheroids at a site called Hare Bay, where it collected core samples. After incorporating the Belle Isle core into the sample, the science team turned their attention to loose spheroids in the surrounding terrain that appeared to have weathered away from nearby rock formations.

This image, a fused supercamera Remote Micro Imager (RMI) mosaic of images taken by NASA's Perseverance Mars rover, shows a portion of the St. Paul's Bay target, located in the lower area of ​​Witch Hazel Mountain on the rim of Jezero Crater. The images reveal hundreds of strange spherical objects that make up the rock. "Perseverance" took this photo on March 11, 2025, the 1,442nd Martian day of the Mars 2020 mission. Image source: NASA/JPL-Caltech/LANL/CNES/IRAP

On the 1555th Martian day, the Perseverance rover went to a target site called "Mount Russell" and conducted a survey of soil rich in spherical particles. The rover carefully surveyed the site using instruments on its robotic arm. SHERLOC's autofocus and environmental imagers and WATSON camera captured detailed, high-resolution images (shown at the top of the page), while PIXL analyzed the chemical elements in the spherical particles and the material surrounding them.

In September 2021, the 198th Martian day of the mission (i.e. Mars day), NASA's "Perseverance" Mars rover used its Watson camera to take this selfie on a rock named "Lochte". Two holes can be seen in the picture, which were left by the detector using a robotic arm to drill core samples. Image source: NASA/JPL-Caltech/MSSS

Although superficially similar to Opportunity's Blueberry, Mount Russell's spheroids have completely different compositions and possible origins. At Meridian Plateau, these spheroids are composed of the mineral hematite and are thought to have formed in groundwater-saturated sediments in Mars' distant past.

In contrast, the globules in Mount Russell are composed of basalt and were likely formed during meteoroid impacts or volcanic eruptions. When a meteoroid hits the Martian surface, it melts rock and ejects molten droplets into the air. These droplets then cool rapidly, solidify into spheres, and rain down on the surrounding area. Alternatively, the globules may have formed from lava during volcanic eruptions.

With this new data, the Perseverance science team will continue to search for the source of these pellets. If they formed from ancient impacts, they may reveal the composition of the meteoroids and the importance of impact craters in Mars' early history. If they were formed during volcanic eruptions, they may preserve clues about past volcanic activity in the area around Jezero Crater. Regardless, these pellets are remnants of a vibrant and vibrant period in Martian history!

Author: Andrew Shumway, postdoctoral researcher at the University of Washington