This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists were shocked when they received the first images of Martian gullies. They were even more shocked as those gullies appeared to change over time.
Their similarities to gullies seen on Earth were uncanny, but all of Earth's gullies are formed by water runoff, and Mars is too cold and has too sparse an atmosphere to have liquid water on its surface. Whatever has been causing those changing gullies couldn't have been water, so what was it? A new paper from Apolline Leclef of the Institut d'Astrophysique Spatiale at Université Paris-Saclay and her colleagues, available on the arXiv preprint server, shows how they are likely caused by CO2 frost turning into a fluid.
To prove this idea, the authors turned to data from two of the longest-standing observers of Mars' environment—Mars Express and the Mars Reconnaissance Orbiter (MRO). They looked at data collected by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on MRO and the OMEGA spectrometer on Mars Express, but focused on a very specific location. Known as Sisyphi Cavi, this system of deep polar pits is situated near the polar ice cap at Mars' south pole.
Crucially, despite being known to have active gullies itself, it is well outside the more temperate latitudes where gullies on Mars usually form. Their first task was to completely disprove the theory that the gullies were driven by water. Water itself has a very specific spectral absorption band at 1.5 μm.
That band was completely absent during the spring, when the CO2 ice that blankets the planet's surface during the winter vanishes. There were some detections of salts and clays, which typically require water to form, but only on the high plateaus and crater rims of the area, not anywhere near where the gullies are located. So, clearly, liquid water was not the cause.
Which turned the researchers' attention to the next potential culprit—geysers. On Earth, we think of geysers as jets of hot water spewing up from inside the Earth's surface. But on Mars, they have a different mechanism, known as the Kieffer geyser mechanism.
Extract — continue reading at the source.
