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

They need to dig more

[hcs_$reboot]

and expect an awful shock when they discover the broken remains of the Statue of Liberty.

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?

[TheSync]

Meteorite data show that Mars had a much denser atmosphere billions of years ago, perhaps as dense as half that of the Earth (now it is only 0.06 times as dense as the Earth's). Back then it had a magnetic field to avoid atmosphere stripping by the solar wind.

Re:No rain?

[Anonymous Coward]

That seems implausible. If the solar wind was strong enough to strip away CO2 and CH4, it would have also been strong enough to strip away water vapor.

The stripping wasn't exactly instant, it would take millions of years for the solar winds to get rid of the atmosphere.
Water vapor would probably one be in the atmosphere for a couple of weeks until it fell down again. Nowhere close to the time needed for solar winds to carry it away.

Also, with "most of the atmosphere" I assume we are meaning just above 50% of it because without atmosphere the water vapor will be the gas with the highest density around and will stay at the bottom.

Re:No rain?

[Rei]

Could have been large impact-driven vaporization events that temporarily create a denser, water-rich atmosphere, perhaps? I haven't read the full study, so I'm not sure what they're positing. Water does need a certain minimum pressure to be able exist as a liquid at all. Hygroscopic salts at high concentrations can let it exist as a liquid at much lower pressures, though I'm not sure how you'd sustain huge brine-filled rivers for billions of years; you'd expect the source of said salts to be quickly exhausted by such flows.

Personally I'm more curious about Venus's rivers, like Baltis Vallis, the longest riverbed in the solar system. We don't even know what fluid carved them, let alone where it came from or where it went. Theories cover everything from liquid sulfur to supercritical CO2, but most likely is that it's thermal erosion by rare (by Earth standards) types of low-temperature lavas, such as carbonatites or similar.

(Love carbonatites... look like crude oil during the day, glow maroon in the dark, flow like water, and rapidly oxidize to bright white after cooling. Also tend to be very rich in valuable minerals)

Re:No rain?

[Gavagai80]

It snows on Mars even today. Not very much, and it's uncertain whether the H2O snow ever reaches the ground (probably only in unusual downdraft events), but it happens. And overnight frosts are common. Go back a billion years and you have enough atmosphere for rain -- especially during a warm period where the CO2 currently frozen into the polar cap was in the air.

Re:No rain?

[Dunbal]

It had a magnetosphere. Then the core cooled and stopped rotating, causing the loss of the magnetic field. The magnetic field of a planet is not some innate property of planetary material - it's caused by movement, rotation, eddies, and whirlpools of liquid iron. The massive volcanoes on Mars point to a past where Mars did have a liquid layer. However the planet has since cooled down, unlike Earth which being much bigger will take more time to cool.

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:No rain?

[RockDoctor]

The atmospheric pressure of Mars obviously varies with altitude (distance from the planet centre). The "zero" for altitude, since there is no sea level to work from, is taken as the point where it has a pressure of 600 Pa (kg/m^2), which is near the middle of the range. That is 0.006 of the atmosphere of Earth. This pressure is below the triple point of water and water ice would directly sublime to the vapour without going through a liquid phase. In the deeper basins of Mars (equivalent to the Dead Sea, Caspian Sea, and Death Valley, but several kilometres deeper) you might be able to get liquid water to be stable, but you'd have to heat it to around 10degC (70 or 80 deg hotter than the general surface) and seal it into a plastic bag to actually get the water to condense again, as the ppH2O (Partial Pressure of water) would be in the bag along with a significant amount of CO2, which would dilute the water vapour, making it harder for "rain" to form.

it'd rain "earlier" than it would in equivalent conditions on Earth.

It'd rain later. Sorry, but Kim Stanley Robinson knew he was playing fast and loose with the gas laws in his fiction, even if some people (Elon Musk, I'm looking at you!) have taken the fiction as fact.

Re:No rain?

[Rei]

With a surface temperature in the region of 450degC,

Venus's surface conditions vary greatly with altitude, and are believed to have varied greatly with time; it's atmosphere is believed to being pushed over tipping points than Earth's. Using today's surface conditions, and a global average at that, to draw conclusions about specific features that formed long ago, isn't really helpful.

But yes, cooling rates on Venus even of regular basaltic lavas (apparently rather MORB-like in most locations, although not all) appear to be much slower than on Earth. Melt also is much more prolific after energetic events; for example, melt pools from large impactors often overflow their craters and flow for significant distances (example).

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.

A river as long as Baltis Vallis - nearly 7000km - is going to have more than ample time for gas exchange during its flow. Also remember that Venus's crust is depleted in water, which reduces viscosity.

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

You're disagreeing with peer-review (note: I did not say carbonatites specifically, but "carbonatites or similar" - carbonatites are one of a few types of low-temperature postulated flows that could have realistically formed such rivers). Higher-temperature magmas simply are not believed to have been capable of flowing such distances with such low viscosities - even in the exotic environment of Venus's surface.

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.

Thankfully for Venus, volcanism isn't exactly rare ;) Venus is exceedingly volcanically active. Most of its surface is basaltic flows. And there are ample signs of secondary differentiation, such as the pancake domes (the leading theory is that they're equivalent to rhyolite domes on Earth). Indeed, we have direct measured evidence of the differentiation from the Soviet landers (Venera+Vega), which measured some basalts so abnormally high in incompatible elements that they were initially thought to have been granite. A number of the studied rock types appear to be various enrichment end-members.

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

They erupt containing large amounts of hygroscopic anhydrides (primarily gregoryite and nyerereite), which quickly absorb water from the air.

They're not panaceas.

"Carbonatites are panaceas" said nobody ever. ;)

Re: No rain?

[drinkypoo]

If only they had listened to the experts!

Perhaps they did, and colonized this planet :p

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.

Re:OK, cool.

[Dunbal]

Any Mars colony would need to be mainly underground - no atmosphere or magnetic field means full exposure to cosmic radiation. That's not healthy for humans. Underground also makes it easier to contain an artificial atmosphere. A sustainable colony would not be possible though. Water or some other source of oxygen would have to be consumed, and waste CO2 dealt with effectively as well. All highly energy intensive. You'd need massive solar arrays, I doubt the atmosphere is dense enough for wind turbines. Or you'd have to bring your own nuclear power plant. Yeah it would be complicated. Not impossible, but very very complicated.

Re:Funny

[johnsie]

Those rovers just evolved over billions of years. They were orginally single cell organisms, and then dogs and then monkeys and then robots. A true product of natural selection and evolution. They were never designed by anyone, they just got there through mutations.

White martians?

[whitroth]

So, unless John Carter really did get back, the White Martians wound up controlling all the others, the green, the red....