NASA’s Perseverance rover captured this image of
spherule-bearing regolith at Rowsell Hill using its arm-mounted WATSON camera
on July 5, 2025 — Sol 1555, or Martian day 1,555 of the Mars 2020 mission — at
the local mean solar time of 12:46:29. WATSON (Wide Angle Topographic Sensor
for Operations and eNgineering) is a close-range color camera that works with
the rover’s SHERLOC instrument (Scanning Habitable Environments with Raman and
Luminescence for Organics and Chemicals); both are located on the turret at the
end of the rover's robotic arm.
NASA/JPL-Caltech
Written by Andrew Shumway, Postdoctoral Researcher at the University of
Washington
It is not common for a rover to
spot nearly perfect spheres in the soil beneath its wheels. Over two decades
ago, the Opportunity rover famously discovered spherules made of hematite
(nicknamed “blueberries”) near its landing site in Meridiani Planum. More recently, the
Perseverance rover has similarly encountered spherules embedded in bedrock and
loosely scattered throughout the region informally called “Witch Hazel Hill.”
In a previous blog post, we described Perseverance’s investigations of a
spherule-bearing outcrop at the “Hare Bay” abrasion patch, where the team later
collected a core. With the “Bell Island” sample added to the rover’s
collection, the science team next decided to take a closer look at loose
spherules in the area, which appear to have eroded out of the nearby
bedrock.
On Sol 1555, while the United
States was celebrating the Fourth of July with hotdogs and fireworks,
Perseverance was hard at work studying spherule-rich regolith at the target
“Rowsell Hill” using the proximity instruments on its robotic arm. SHERLOC’s Autofocus
and Context Imager and WATSON camera both captured high resolution pictures of
the target (shown above), while PIXL measured the elemental makeup of the
spherules and surrounding grains.
Despite their superficial
similarity to Opportunity’s “blueberries”, the spherules at “Rowsell Hill” have
a very different composition and likely origin. In Meridiani Planum, the
spherules were composed of the mineral hematite and were interpreted to have
formed in groundwater-saturated sediments in Mars’ distant past. By comparison,
the spherules in “Rowsell Hill” have a basaltic composition and likely formed
during a meteoroid impact or volcanic eruption. When a meteoroid crashes into
the surface of Mars, it can melt rock and send molten droplets spraying into
the air. Those droplets can then rapidly cool, solidifying into spherules that
rain down on the surrounding area. Alternatively, the spherules may have
formed from molten lava during a volcanic eruption.
With these new data in hand, the Perseverance science team continues to search for answers about where these spherules came from. If they formed during an ancient impact, they may be able to tell us about the composition of the meteoroid and the importance of impact cratering in early Mars’s history. If they instead formed during a volcanic eruption, they could preserve clues about past volcanism in the region around Jezero crater. Either way, these spherules are a remnant of an energetic and dynamic period in Mars’ history!
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