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Mars Earth Space

Mars Had Big Rivers For Billions of Years, Study Suggests (space.com) 77

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.

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Mars Had Big Rivers For Billions of Years, Study Suggests

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  • by hcs_$reboot ( 1536101 ) on Friday March 29, 2019 @02:14AM (#58352308)
    and expect an awful shock when they discover the broken remains of the Statue of Liberty.
  • No rain? (Score:5, Insightful)

    by MS ( 18681 ) on Friday March 29, 2019 @02:24AM (#58352324)

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

    • Re:No rain? (Score:5, Interesting)

      by TheSync ( 5291 ) on Friday March 29, 2019 @02:45AM (#58352354) Journal

      Meteorite data [sciencedaily.com] 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.

      • But the summary says that the rivers continued to flow after most of the atmosphere had been stripped away.

        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.

        • Re: (Score:2, Interesting)

          by 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.

          • Which begs the question how, without magnetosphere, an atmosphere formed in the first place - or equally how microbial life established here so rapidly, with water present on both bodies. No mention of the rovers picking up traces of Melange either, hmmm....
            • Re:No rain? (Score:5, Informative)

              by Dunbal ( 464142 ) * on Friday March 29, 2019 @08:37AM (#58353000)
              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.
              • Earth also likely has a lot more radioactive materials in its core that are decaying and producing heat . . . possibly an even higher percentage than our planet's size would indicate due to the probable nature of the collision that created the Moon (it got the light stuff, we kept the heavier stuff). The Moon also creates a tide (even in the Earth's core) which probably helps keep things moving to produce the magnetosphere.
          • by Dunbal ( 464142 ) *
            I'm guessing the magnetic field didn't just disappear overnight either. These are obviously processes that occurred over geological time.
          • it would take millions of years for the solar winds to get rid of the atmosphere.

            On geological time scales, a million years is the blink of an eye. The summary claims that liquid water persisted for billions of years after the atmosphere was mostly gone.

            I don't see how that is plausible. Even near freezing, water has a vapor pressure over 600 pascals, or 0.006 atm.

        • Re:No rain? (Score:4, Interesting)

          by Rei ( 128717 ) on Friday March 29, 2019 @05:22AM (#58352554) Homepage

          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 [google.is], 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 [youtube.com] during the day, glow maroon [google.is] 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? (Score:5, Insightful)

            by RockDoctor ( 15477 ) on Friday March 29, 2019 @10:25AM (#58353500) Journal

            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 [wikipedia.org] 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

            • by Rei ( 128717 )

              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

        • 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.

        • by phayes ( 202222 )

          The word "Most" in this context only means over 50%, not 99%.

          The top of Mt Everest has less than a third of the atmospheric pressure at sea level and liquid water can be present if warm enough.

          Thus it is entirely plausible for water to have flowed on Mars after it had lost most of it's atmosphere (but before it lost to the point it is presently).

        • 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.

          Correct! Now, how long does it take for water to sublimate into vapor to be stripped away? Does it happen all at one time?

    • Comment removed based on user account deletion
      • Re:No rain? (Score:4, Informative)

        by RockDoctor ( 15477 ) on Friday March 29, 2019 @10:39AM (#58353576) Journal
        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 [wikipedia.org] 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.

  • Years after the rivers dried up followed by countless millennia of wind erosion we can still see them as if it was relatively recent. Not filled with sands, not eroded away, perhaps even enhanced with the edges smoothed a bit. What does that tell us? It would be neat to have a computer simulation to reverse the erosion to see what it may have looked like before.
    • Re: Erosion (Score:2, Insightful)

      by 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.

      • Yet it still managed to blot out the mars rover in short order.
        • by Anonymous Coward

          Because it has no water anymore that washes ultrafine particles from the atmosphere and binds them in sediments.

    • What does that tell us

      That is very definitely not the methodology or data sets that the paper describes. Did you actually read it? It's perfectly comprehensible, doesn't use too many long words, and only takes about 3/4 hours.

  • OK, cool. So what?
  • This article [sciencealert.com] includes several references on giving Mars an artificial magnetosphere with machine(s) that are within existing human capability to build. With a functional BFR [wikipedia.org] class rocket, we would have the capability to actually deploy such a system.

    Once such a machine were turned on the atmospheric pressure and temperature on Mars would rise sufficiently within a handful of years to remove the need to wear a space suit. Liquid water could (and would) exist in lakes, rivers, and rain. The people who depl

    • by Dunbal ( 464142 ) *
      Drivel. I'm guessing once you manage to create a planet sized magnetic field (powered by magic and faerie dust), the atmosphere would just appear out of nowhere.
      • by DanDD ( 1857066 )

        Pretty much, yes, Martian atmosphere would appear from the melting of existing CO2 and water ice which would no longer be driven off into space. Global warming would speed the process.

        I freely admit to being an optimist.

        Our own experiments on Earth with greenhouse gasses and global warming might provide some useful data, although I'd rather experiment on Mars.

        https://www.sciencedirect.com/... [sciencedirect.com]

    • Once such a machine were turned on the atmospheric pressure and temperature on Mars would rise sufficiently within a handful of years to remove the need to wear a space suit.

      "a handful of years" - well, a handful of millennia, unless someone provides some energy from somewhere. Quite a lot of energy - I really should work out how much one day.

      Oh, and that would be if you moved most of the mass of the Asteroid Belt - the icy bits - from flying through a few hundred cubic.AU of space onto the planet's surfac

      • by DanDD ( 1857066 )

        Stop the current Mars atmospheric loss due to solar winds and atmospheric density and temperature will rise. The Sun provides the significant energy needed to create a runaway greenhouse effect on Mars, which really isn't that far away from an energy standpoint. Mars is, after all, in the habitable zone [wikipedia.org]. The energy needed to power the artificial magnetosphere is not insignificant, but on the scale of existing human ability.

        Around 600 BC some folks thought it would be fun to dig a 4 mile long canal across

  • The very first telescopes trained on Mars detected the "canals".
  • I read that as "Mars Had Big Rovers For Billions of Years".
    • 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.
  • Wow, this information is COMPLETELY USELESS.
  • by whitroth ( 9367 ) <whitroth@@@5-cent...us> on Friday March 29, 2019 @11:30AM (#58353826) Homepage

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

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