More than two decades after NASA's Spirit rover fell silent on Mars, its data still has secrets to give up. Professor Paulo de Souza of Edith Cowan University has reanalyzed archived measurements from the rover's miniaturized Mössbauer spectrometer, MIMOS II, and found evidence of water-related minerals that were too faint to spot during the mission itself.
From early 2004, Spirit explored the Gusev crater, using MIMOS II to identify iron-bearing minerals by measuring how iron atoms absorb gamma rays. The rover had to share limited time, power and memory among a full suite of instruments, so individual measurements were often brief, producing spectra with poor statistics that masked minor iron phases.
To overcome that limitation, de Souza combined readings from 32 undisturbed soil targets that Spirit examined over 2,062 Martian days, spanning temperatures from 180 to 300 K. Because temperature swings within about a 10-K range don't meaningfully distort the spectra of basaltic material, he merged data across those windows first, then combined all temperature ranges into a single composite spectrum — roughly six days of equivalent measurement time packed into one dataset.
The consolidated spectrum showed the expected common Martian minerals such as olivine and pyroxene, plus a poorly crystalline, paramagnetic iron-bearing phase. But it also revealed clearer signatures of magnetite and crystalline hematite than earlier single-experiment analyses could pick out.
"One of the most important discoveries was finding crystalline hematite in ordinary Martian soil," de Souza said. "This mineral's widespread presence suggests not only that water was present, but that significant areas of Mars may have once been covered by water."
The study was published in the journal Interactions.
