Reanalyzed data from NASA’s Spirit rover indicate that Martian soil in Gusev Crater contains iron-bearing minerals, including crystalline hematite and altered magnetite, that were too weak to identify during the mission’s original analyses.
“Beginning in early 2004, NASA’s Spirit rover explored Gusev Crater on Mars, using a suite of scientific instruments to study the geology and mineralogy of soils, rocks, meteorites and dust collected by onboard magnets,” said Professor Paulo de Souza, a researcher at Edith Cowan University.
“One of the rover’s key instruments was MIMOS II, a miniaturized Mössbauer spectrometer designed to identify iron-bearing minerals.”
“Over 2,062 Martian days, NASA’s Mars Exploration Rovers investigated the Red Planet’s surface to determine whether Mars had once been a wetter world.”
For the new study, Professor de Souza reexamined measurements collected by Spirit’s MIMOS II spectrometer. The instrument identifies iron-rich minerals by measuring how iron atoms in a sample absorb gamma rays.
However, Spirit had to divide its limited operating time, power and memory among numerous scientific instruments. As a result, many Mössbauer measurements were relatively short and produced spectra with limited statistical quality.
That limitation made it challenging to detect minor iron-bearing mineral phases that represented only a small portion of the Martian soil’s overall mineral composition.
To improve the signal, Professor de Souza combined measurements from 32 undisturbed soil targets studied by Spirit in Gusev Crater over 2,062 Martian days. The observations covered temperatures ranging from 180 to 300 K.
Temperature variations of approximately 10 K do not significantly change the spectra of basaltic materials. The researcher therefore combined measurements within these temperature ranges before merging them into a single composite spectrum.
The resulting dataset represented approximately six days of equivalent measurement time, providing a much clearer view of the minerals present in Martian soil.
The consolidated Mössbauer spectrum confirmed common Martian soil minerals, including olivine and pyroxene, as well as a poorly crystalline, paramagnetic iron-bearing phase.
It also revealed stronger signatures of magnetite and crystalline hematite than had been detected in earlier analyses of individual experiments.
“One of the most significant findings was the identification of crystalline hematite in ordinary Martian soil,” Professor de Souza said.
“The widespread occurrence of this mineral suggests that water was present on Mars and that substantial regions of the planet may once have been covered by water.”
The study was published in the journal Interactions.
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P. de Souza. 2026. A consolidated Mössbauer spectrum for undisturbed soils from Gusev Crater, Mars. Interactions 247, 278; doi: 10.1007/s10751-026-02625-4
Source: www.sci.news