Martian gullies as seen in the top image from HiRISE on NASA’s Mars Reconnaissance Orbiter resemble gullies on Earth that are carved by liquid water. However, when they are observed with the addition of mineralogical information from CRISM (bottom), no evidence for alteration by water appears. Photo: NASA/JPL-Caltech/UA/JHUAPL In 2014, scientists at NASA announced that the gullies on Mars’ surface — whose discovery in 2000 caused widespread excitement among many who perceived them as evidence of flowing water — were formed by the seasonal freezing of carbon dioxide. Now, two years later, further analysis of data gathered by the Mars Reconnaissance Orbiter (MRO) bolsters the case against the structures being formed by flowing liquid water.
Researchers from the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, examined high-resolution data gathered by the MRO from more than 100 gully sites throughout Mars, and found no mineralogical evidence for water or its by-products. These findings, detailed in a study published in the Geophysical Research Letters, would now allow scientists to narrow their theories about how the Martian gullies form.
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