It certainly leaves plenty of work available for the High-Resolution Imaging Science Experiment (HiRISE) camera on the MRO, both of which are in excellent health despite spending more than a decade at Mars.
Another new paper in the journal Icarus identifies 239 candidate and confirmed RSL sites within Valles Marineris alone, which is a large canyon that stretches across the equivalent distance of the United States. The valley hosts half of all globally known RSL locations, and given its vast size there are always at least some RSL growing within, "regardless of the season", the paper abstract reads.
"If RSL are caused by water, such a long active season at hundreds of [Valles Marineris] RSL sites suggests that an appreciable source of water must be recharging these RSL," says the paper, which is led by David Stillman at the Southwest Research Institute. The research team adds that modelling indicates a melting temperature of at least -16 degrees Fahrenheit would be needed to make the briny water flow.
"The mechanism(s) by which RSL are recharged annually remain uncertain. Overall, gaining a better understanding of how RSL form and recur can benefit the search for extant life on Mars and could provide details about an in situ water resource," the paper adds.
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Zurek said his team knows there is still a lot to learn about the water activity, especially how RSLs could form in a Martian environment (low pressure, very cold) as opposed to Earth. There are laboratory studies going on to try to get the temperature cycle exactly right; it's hard to replicate because the soil composition is difficult to forecast beyond the salt concentration, he said.
"We are arguing for more work there. Also, we should map out where we think these features might be," he added. While HiRISE has been imaging Mars for more than a decade, it has only mapped out 3 percent of the planet in high resolution. One of the spots it's keeping an eye on now is Gale Crater to see if those streaks are RSLs, which should become clear within the next Martian year (the equivalent of two years).
Zurek added there still is time for MRO to collect much more data, as the orbiter is forecast to work at Mars until at least 2023. This would allow MRO to also act as a communications relay for the Mars 2020 rover, which is expected to land somewhere on Mars in 2021.
Image (top): A 3-D computer model of dark streaks, known as "recurring slope lieae", on the walls of Garni Crater on Mars. Data came from the NASA Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment (HiRISE) camera. Credit: NASA/JPL-Caltech/Univ. of Arizona WATCH VIDEO: Why Can't We Livestream From Mars?