On August 28th, 2016 we learned about

Seasonal streaks on Mars don’t show expected shifts in temperature

For the past few summers, we’ve detected seasonal changes on Mars that may be linked to the presence of water. Nobody is suggesting that this summer will eventually be swimsuit season on the Red Planet though, as we’re only finding possible traces of moisture, rather than anything deep enough to even dip your toes into. That said, the past few Martian summers have included the appearance of strange, dark streaks along some sandy hillsides, which may be tied to the presence of H2O in the soil. Newer measurements suggest that the amount of water involved in these sandy streaks is minimal to say the least, being just shy of being completely arid.

Not wet enough for warmth

We don’t have a rover at the site of the seasonal streaking, but the Mars Odyssey Orbiter was still able to measure some of the activity from space. If these streaks, also known as recurring slope lineae (RSL) contained more water than the nearby soil, they would absorb heat from the sun differently than drier dirt. With that model in mind, the spacecraft used its Thermal Emission Imaging System (THEMIS) to take measurements of various streaking locations and their immediate surroundings.

While the streaks were still turning up in the sand as usual, their expected shifts in temperature turned out to be more elusive. The THEMIS measurements found next to no differences at all, meaning that while some water may be present, there is hardly anything there. Researchers calculated that there could be no more than an ounce of water per two pounds of soil, which is comparable to the driest deserts on Earth. The team suspects that this water may be in the form of hydrated salts, with tiny amounts of water being absorbed from the atmosphere, rather than anything resembling a droplet anywhere.

Long-retired rivers

Even if Mars isn’t looking too wet this summer, a separate study has found that we may just be a few billion years too late for some really lovely shores. High resolution images of geographic features in a region known as Arabia Terra look like perfect matches for dried and buried riverbeds. These inverted channels are now filled with sand and gravel, matching features on Earth known to have once been flowing rivers. While things are unfortunately parched now, it appears that Mars was once home to oceans, rivers, and even flood plains.

Source: Test for Damp Ground at Mars' Seasonal Streaks Finds None by Tony Greicius, NASA

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