Oct 282017
 

Here’s an odd thought:

Did Ceres once have an ocean?

The dawn spacecraft has detected minerals that seem to indicate that there was once liquid water on the surface. By “once,” that means “4 billion years ago.” The evidence indicates that there is still substantial water bound upon the surface “rock” of Ceres, with the possibility of meaningful amounts of liquid water still existing under the surface.

But with a surface gravity of only 0.029 g, back when it had an ocean it must have been a bizarre place. That’s far too low a surface gravity (more specifically, far too low of an escape velocity) for Ceres to have retained any sort of atmosphere. Air would quickly just… drift away to space. So the ocean must have been in a constant state of near-boiling, with an astonishing evaporation rate. The atmosphere must have been largely water vapor; the atmosphere would blow away, forming a cometary tail likely to have been pretty impressive. This would have been while planets like Earth were still in the process of being formed, so the entire solar system would likely have been a busy place, with *lots* of giant comet-like objects like Ceres.

 

 Posted by at 8:44 am
  • Bob

    Everybody goes on and on about Mars having life. I think a more likely candidate is (or was) Venus. Billions of years ago when the Sun was cooler Venus probably had oceans. Then the Sun got hotter and the Greenhouse Effect set in and Venus became too hot for life (something similar is in store for Earth). I guess we’ll never know.

    • Scottlowther

      Depends how you define “we.” You and I and other schmoes currently alive, almost certainly not. But future folk could well terraform Venus to where paleontologists could find native fossils.

      • se jones

        find native Venus fossils? Very very unlikely, the Venusian periodic magma oceans would erase anything from the planet’s early history. However, if -somehow- life evolved multi-cellular forms on Venus before things went to heck, fossils may have been blasted into space by big impacts, left to wander until the naked monkeys on the third rock find them.

    • Paul451

      Venus underwent a resurfacing event around half a billion years ago. That would be the main source of the current atmosphere, and hence responsible for the current conditions. It’s not due to the increase in solar output.

      • se jones

        “…resurfacing event …the main source of the current atmosphere, and hence responsible for the current conditions”

        au con·traire.
        The global volcanic events are made possible by the atmosphere, not the other way around. Venus’s global ocean of searing hot super-critical CO2 (aka atmosphere) has a profound effect on the planet’s geophysics. The hydration of the Earth’s oceanic plates, lowers their melting point and causes them to be more ductile, this enables our style of plate tectonics. Plate tectonics enables the Earth’s interior to shed heat through the steady creation (and subsequent subduction) of new ocean crust along the plate boundaries.

        Venus’s “style” of tectonics is to produce massive, global, short lived “resurfacing events” every few hundred million years. The hyper dry hot crust is brittle and (mostly) uniformly buoyant all over the planet thanks to the super hot atmosphere, this locks that thin, tough crust in place, essentially creating one solid tectonic plate all over the planet. With no mechanism to create mobile plates, the Venusian crust just sits there trapping the interior heat until a critical temperature is reached, at that point the tensile strength of the crust drops to the point where is just falls apart and allows the magma from Venus’s interior to poor out -sort of everywhere all at once.

        This periodic global magma ocean, doesn’t significantly alter the composition or pressure of the super-critical CO2 ocean, but the excess heat released from the planet’s interior should have a surprising side effect on Venus’s atmosphere -during the global resurfacing events, the sulfur droplets that hide our view of the surface during the present epoch will undergo a phase change, causing the atmosphere to become transparent! That transparent atmosphere will help the global magma ocean to radiate its heat to space, thus ending the resurfacing event and leading to a new cycle.

        “It’s not due to the increase in solar output”. This is true.

        so there ya go

  • Herp McDerp

    That furious evaporation rate might have helped to preserve the ocean. Evaporative cooling would have created a layer of ice at the surface that sealed off the water from the surrounding near-vacuum.

    • se jones

      Herp, just cause water is frozen, it doesn’t just sit there, ice sublimates (you know – Aw).
      Out in the outer solar system the vapor pressure of ice is low enough to ignore (mostly) but at Ceres solar Insolation would probably make an exposed ocean sublimate away over a short (geologic) time period.

  • Bob

    I can’t see us ever Terra forming Venus. Too far Sunward from the habitable zone. Mars maybe but it will take heroic efforts and might not be worth the trouble. What we really need is a FTL drive so we can go find habitable planets around other stars (if there are any).

    • Scottlowther

      Terraforming Venus is doable in several ways. Easiest would be to simply build cities that float above the clouds suspended from vast hydrogen balloons. The air is cool and dense above the clouds. Over the millenia the clouds below would be mined and processed and thinned, terraforming would be a byproduct of the floating arcologies above. Another approach would be to build a ring system . My preference would be a ring made of sulfur chunks shot up from below and rock dust from water bearing comets parked in Venus orbit, the water dropped down.

      • publiusr

        This is what I thought interesting

        “The experiments, performed using the Vertical Gun Range at NASA’s Ames Research Center, suggest that when asteroids and other impactors hit Ceres, much of the impact material remains on the surface instead of bouncing off into space. The findings suggest the surface of Ceres could consist largely of a mish-mash of meteoritic material collected over billions of years of bombardment.”

        http://www.spacedaily.com/reports/What_smacks_into_Ceres_stays_on_Ceres_999.html

        The best place to mine–lower gravity than the Moon–but there is a down–so things don’t float off.

        This also interests me
        https://phys.org/news/2017-09-hubble-unique-solar.html

        Tie a tether to these things (bag the best parts of them first–then pull together until you have artificial gravity.

      • Bob

        I don’t doubt there are ways to make Venus habitable. But would it stay habitable? It’s still inside the Venus Zone https://www.centauri-dreams.org/?p=31533

      • se jones

        The most interesting terraforming method to my mind, is putting a huge sun shade at the Solar/Venus L1 point. Cut off solar insolation and the Venusian CO2 ocean (aka atmosphere) will collapse into a global frozen ocean of “dry ice” in only a hundred years or so.

        Yeah…I always assumed it would take thousands of years for the planet to cool enough for this to happen, but McKay et al. ran the numbers and showed it will happen rather quickly. The tiny surfer dioxide droplets in the CO2 ocean are fantastically good radiators (https://arc.aiaa.org/doi/abs/10.2514/3.25077). Once the super-critical CO2 has radiated most of its heat to space, the hot surface rocks will cool very rapidly. The Venus interior produces a surface flux of only ~100mW/m^2, so the rock being a tremendously good insulator, will not pass on enough interior heat to keep the CO2 from freezing out.

        Once the global frozen CO2 ocean forms, the solar shade can be adjusted so that the out-gassing from Venusian volcanic hot spots, plus a small solar input will keep the new CO2 atmosphere at about one bar.

        The humans can then build domed cities up on the solid ground of the mountains of the Ishtar and Aphrodite Terra highlands.

        The air will have to be kept at -109.3 F to maintain the frozen ocean, but with a breathing mask and really good winter gear, humans can walk around outside the domes with ease. Good winter gear on Venus…irony of irony.

        The 1bar atmosphere is plenty to shield from GCRs, and I wouldn’t worry about solar wind erosion of the “air”, there will be plenty to spare from the frozen CO2 ocean.

        A 24hr day/night cycle would be nice, but I recon the sun shade could be engineered to simulate an earthly cycle.

        • se jones

          A 24hr day/night cycle would be nice, but I recon the sun shade could be engineered to simulate an earthly cycle

          addendum: obviously you’ll need huge reflectors on the night side to beam sunlight to the dome cites for the 24hr circadian cycle. Easy as cake right?