Mars Had Big Rivers For Billions of Years, Study Suggests (space.com)

A new study suggests that Mars once had giant rivers larger than anything on Earth after the planet lost most of its atmosphere to space. "That great thinning, which was driven by air-stripping solar particles, was mostly complete by 3.7 billion years ago, leaving Mars with an atmosphere far wispier than Earth's," reports Space.com. "But Martian rivers likely didn't totally dry out until less than 1 billion years ago, the new study found." From the report: "We can start to see that Mars didn't just have one wet period early in its history and then dried out," study lead author Edwin Kite, an assistant professor of geophysical sciences at the University of Chicago, told Space.com. "It's more complicated than that; there were multiple wet periods." The team's work suggests that Martian rivers flowed intermittently but intensely over much of the planet's 4.5-billion-year history, driven by precipitation-fed runoff. The rivers' impressive width -- in many cases, more than twice that of comparable Earth catchments -- is a testament to that intensity.

It's unclear how much water Martian rivers carried, because their depth is hard to estimate. Determining depth generally requires up-close analysis of riverbed rocks and pebbles, Kite said, and such work has only been done in a few locations on Mars, such as Gale Crater, which NASA's Curiosity rover has been exploring since 2012. The ancient Mars rivers didn't flow in just a few favored spots; rather, they were distributed widely around the planet, Kite and his colleagues found.

Comments

No rain?

[MS]

Without atmosphere, there's no rain.
And without rain, how can rivers be fuill of water for billions of years?!?

Re:No rain?

[RockDoctor]

I haven't read the full study, so I'm not sure what they're positing.

I just did RTFP, and it is a lot more tentative than the press blurb makes out. As normal.

Could have been large impact-driven vaporization events that temporarily create a denser, water-rich atmosphere, perhaps?

They don't much discuss that, but throughout they emphasis that they're examining peak flow rates, not average (mean), median or modal flow rates. That is certainly compatible with thee flows only occurring in the period following large impacts releasing a substantial temporary increase in atmospheric pressure. Then, the water would rain out (over a period) as the atmosphere and planet surface cools, producing large if temporary run-offs. Then the CO2 would freeze out onto the ice caps and into the soil before being buried again by dust. Lather, rinse, repeat, with a caveat that when you put water high into the atmosphere, some of it gets photolytically stripped to release hydrogen to space and oxygen (which goes into the sol as iron-3 oxide). Much as has been modelled previously.

Their synthetic figure 5 certainly shows that sporadic precipitation events their vision, not continuous precipitation through the Amazonian, Noachian &/or Hesperian.

though I'm not sure how you'd sustain huge brine-filled rivers for billions of years;

That is certainly the image that many commentators here have. Possibly also the writers of the press blurb.

It's not in the paper.

It's not in their model.

It's not in their text.

It's not in their figures.

This is why reading the "puff" press releases is normally a complete waste of time. Just go get the paper - it's quicker than building up a idea which the scientists involved are simply not discussing, then having to tear down that misconception and start again from scratch.

Personally I'm more curious about Venus's rivers,[...] but most likely is that it's thermal erosion by rare (by Earth standards) types of low-temperature lavas, such as carbonatites or similar.

With a surface temperature in the region of 450degC, the cooling rates of lavas are going to be very different to what we're familiar with on Earth. Compounding that, the high ppCO2 in the atmosphere is going to reduce devolatilisation of the lavas, retaining their initial low viscosity for ... a hard to calculate amount. Don't get me wrong, carbonatites are fascinating (one of my friends while doing my degree was doing his PhD in UK carbonatites- fascinating rocks!), but such exotic melts are probably not necessary to postulate for these long Venusian channels (NB : Schiaparelli's warning : "channels" without implication about the origin of the structure). These magma types are "exotic" on Earth because they're at the end of a differentiation process - to form a cubic km of carbonatite melt you'd need to start with a couple of hundred cubic km of regular basalt, and you get that by processing around 10000 cubic km of mantle-like material (which is, unsurprisingly, close to the average of non-ice, non-H/He material in the solar system). Those many cubic km of other materials processed to produce your carbonatites will be somewhere, and you'll see the structures they generate far more often.

and rapidly oxidize to bright white after cooling.

That's probably materials like sodium carbonate and sodium hydrogen carbonate weathering out very rapidly as the rocks self-metamorphose on their own residual liquors. And it's the case for carbonatite lavas. Far larger volumes of carbonatites solidify below ground as relatively small bosses and cupolas on the margins of per-alkaline igneous intrusions.

Also tend to be very rich in valuable minerals)

They ca

Re: Erosion

[Anonymous Coward]

It tells us the atmosphere is so thin that it can't lift enough abrasive material in million of years to abrade old river beds.