The dark, fingerlike features that creep down steep Martian slopes in warm weather continue to puzzle scientists.
These "recurring slope lineae" (RSL), which have been spotted by NASA's Mars Reconnaissance Orbiter (MRO) at low and middle latitudes on the Red Planet, fade during cooler months but come back again annually at nearly the same locations over multiple Martian years.
Scientists continue to debate the true nature of the RSL phenomenon; no guess as to what they are and why they occur yet satisfies all observations. And just how RSL sites should be explored generates spirited debate, as evidenced by the discussions that emerged during the second Mars 2020 Landing Site Workshop, which was held last month in Monrovia, California. [Photos: The Search for Water on Mars]
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