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posted by martyb on Friday February 02 2018, @03:30PM   Printer-friendly
from the 'All-these-worlds-are-yours,-except-Europa.-Attempt-no-landing-there." dept.

Future Europa landers may be in danger of sinking into a surface less dense than freshly fallen snow:

Space scientists have every reason to be fascinated with Jupiter's moon Europa, and, in 2017, NASA and the European Space Agency (ESA) announced they are planning a joint mission to land there. As the video above explains, this little moon is thought to have a liquid ocean submerged beneath an icy crust. Scientists believe it could host extraterrestrial life. But Europa's surface is much more alien than any we've ever visited. With its extremely thin atmosphere, low gravity – and a surface temperature of some -350 degrees F. (–176 °C.) – Europa might not be kind to a landing spacecraft. The moon's surface might be unexpectedly hard. Or – as evidenced by a study from the Planetary Science Institute announced on January 24, 2018 – Europa's surface might be so porous that any craft trying to land would simply sink.

The study – published in the peer-reviewed journal Icarus – comes from scientist Robert Nelson. If you're a student of space history, its results might sound familiar. Nelson pointed out in his statement:

Of course, before the landing of the Luna 2 robotic spacecraft in 1959, there was concern that the moon might be covered in low density dust into which any future astronauts might sink.

Now Europa is the source of a similar scariness, with Nelson's study showing that Europa's surface could be as much as 95 percent porous.

Laboratory simulations of planetary surfaces: Understanding regolith physical properties from remote photopolarimetric observations (DOI: 10.1016/j.icarus.2017.11.021) (DX)


Original Submission

Related Stories

Amino Acids Could Exist Just Centimeters Under Europa's Surface 15 comments

Europa Lander May Not Have to Dig Deep to Find Signs of Life

If signs of life exist on Jupiter's icy moon Europa, they might not be as hard to find as scientists had thought, a new study reports. [...] NASA aims to hunt for such samples in the not-too-distant future. The agency is developing a flyby mission called Europa Clipper, which is scheduled to launch in the early 2020s. Clipper will study Europa up close during dozens of flybys, some of which might be able to zoom through the moon's suspected water-vapor plumes. And NASA is also working on a possible post-Clipper lander mission that would search for evidence of life at or near the Europan surface.

It's unclear, however, just how deep a Europa lander would need to dig to have a chance of finding anything. That's because Europa orbits within Jupiter's radiation belts and is bombarded by fast-moving charged particles, which can turn amino acids and other possible biosignatures into mush.

That's where the new study comes in. NASA scientist Tom Nordheim and his colleagues modeled Europa's radiation environment in detail, laying out just how bad things get from place to place. They then combined these results with data from laboratory experiments documenting how quickly various radiation doses carve up amino acids (a stand-in here for complex biomolecules in general).

The researchers found significant variation, with some Europan locales (equatorial regions) getting about 10 times the radiation pounding of others (middle and high latitudes). At the most benign spots, the team determined, a lander would likely have to dig just 0.4 inches (1 centimeter) or so into the ice to find recognizable amino acids. In the high-blast zones, the target depth would be on the order of 4 to 8 inches (10 to 20 cm). (This is not to imply that potential Europan organisms would still be alive at such depths, however; doses there are high enough to cook even the hardiest Earth microbes, study team members said.)

Also at Motherboard and Gizmodo.

Preservation of potential biosignatures in the shallow subsurface of Europa (DOI: 10.1038/s41550-018-0499-8) (DX)

Biosignature hide and seek (DOI: 10.1038/s41550-018-0542-9) (DX)

Ice Spikes Could Complicate Europa Landings 11 comments

Fields of five-story-high ice blades could complicate landing on Jupiter moon

Probes have shown that Europa's ice-bound surface is riven with fractures and ridges, and new work published today in Nature Geosciences suggests any robotic lander could face a nasty surprise [DOI: 10.1038/s41561-018-0235-0] [DX], in the form of vast fields of ice spikes, each standing as tall as a semitruck is long.

Such spikes are created on Earth in the frigid tropical peaks of the Andes Mountains, where they are called "pentinentes,"[sic] for their resemblance to devout white-clad monks. [...] Pentinentes[sic] have already been seen on Pluto. And by calculating other competing erosional processes on Europa, such as impacts and charged particle bombardment, the new work suggests the vaporization of ice would be dominant in its equatorial belt, forming pentitentes[sic] 15 meters tall spaced only 7 meters apart. Such formations could explain, the authors add, why radar observations of the planet dip in energy at its equator, the pentinentes[sic] scattering the response. But the ultimate proof of whether Europa's belly will be off limits to landing will come when the Clipper arrives in the mid-2020s.

[Update: It's penitentes. Ed.]

First it was slush. Now it's spikes. Attempt no landing there.

Europa.

Also at Science News and The Verge.

Related:
NASA Releases Europa Lander Study 2016 Report
Amino Acids Could Exist Just Centimeters Under Europa's Surface


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  • (Score: 0) by Anonymous Coward on Friday February 02 2018, @03:33PM

    by Anonymous Coward on Friday February 02 2018, @03:33PM (#632020)

    and if they still sink then, have it move around?

  • (Score: 0) by Anonymous Coward on Friday February 02 2018, @03:42PM (4 children)

    by Anonymous Coward on Friday February 02 2018, @03:42PM (#632025)

    ALL THESE WORLDS ARE YOURS EXCEPT EUROPA

    ATTEMPT NO LANDING THERE

    • (Score: 2) by bzipitidoo on Friday February 02 2018, @04:33PM (1 child)

      by bzipitidoo (4388) on Friday February 02 2018, @04:33PM (#632042) Journal

      The intelligent life forms who live on Europa purposely made the surface porous to keep curious Earthlings from landing any probes on their world.

      • (Score: 2) by All Your Lawn Are Belong To Us on Friday February 02 2018, @04:48PM

        by All Your Lawn Are Belong To Us (6553) on Friday February 02 2018, @04:48PM (#632047) Journal

        The monolith intelligent life forms who live on Europa purposely made the surface porous to keep curious Earthlings from landing any probes on their world.

        FTFY.

        And when I started reading the story I thought exactly of the similarity to the Moon quote. Hopefully we'll have better experimentation before dropping a multi-instrument probe there like the study indicates. (Or do you build a much less costly probe and piggy back it on some other project where the orbital mechanics work out to send it along...)

        --
        This sig for rent.
    • (Score: 5, Touché) by maxwell demon on Friday February 02 2018, @04:54PM

      by maxwell demon (1608) on Friday February 02 2018, @04:54PM (#632051) Journal

      All these lines are yours, except the dept. line. Attempt no reading there.

      --
      The Tao of math: The numbers you can count are not the real numbers.
    • (Score: 2) by krishnoid on Friday February 02 2018, @07:48PM

      by krishnoid (1156) on Friday February 02 2018, @07:48PM (#632126)

      ITS JUST REALLY SQUISHY

  • (Score: 2, Interesting) by Anonymous Coward on Friday February 02 2018, @03:59PM (6 children)

    by Anonymous Coward on Friday February 02 2018, @03:59PM (#632033)

    If it's going to sink anyway, make sure there is a suitable "buoy" that can stay on the surface[1]. Use it to keep an antenna on the surface and send back sensor readings through a very long cable as the probe sinks.

    [1] This might be a hollow sphere made of some material that is strong and tough, at those very low temperatures.

    • (Score: 2) by Immerman on Friday February 02 2018, @05:42PM (3 children)

      by Immerman (3985) on Friday February 02 2018, @05:42PM (#632066)

      You've just described, I think, most of the suggested Europa missions, which mostly plan to leave a tethered communications buoy on the surface and melt their way down to the ocean where the real interesting stuff might be. The real problem though is density - assuming the surface is water ice (0.9g/cm3), and 95% porous in vacuum, you're talking 0.045g/cm3, or about 1/4 as dense as helium gas on Earth. Of course any sort of inflatable "beach ball" can have near-vacuum pressure inside it, but you still have to contend with the average density of the of the skin, and more importantly the communication apparatus. to deal with.

      Not that it couldn't be done - a giant inflatable beach ball bigger than the expected landing rocket crater, with a metallic lower half acting as a communications dish is probably feasible. But almost certainly NOT the design you'd want if the surface was more durable. Nor if there's potential for shards of harder substances that could puncture the ball. There's also the problem of deploying such a ball in the time between touchdown and sinking too far beneath the surface to be useful - it's going to have to be a hell of a balloon to survive rapid inflation at -350F. And you probably can't warm it up or it'll just melt its way down into the surface as well.

      • (Score: 0) by Anonymous Coward on Friday February 02 2018, @07:42PM

        by Anonymous Coward on Friday February 02 2018, @07:42PM (#632124)
      • (Score: 2) by edIII on Friday February 02 2018, @08:19PM (1 child)

        by edIII (791) on Friday February 02 2018, @08:19PM (#632141)

        I'm not sure there is a technical solution we can pull off. What you've described doesn't seem like anything could land on it, since it seems akin to landing a molten hot bowling ball on top of a 10 foot high column of Cotton Candy without the bowling ball sinking to the bottom of course. The ball idea sounds neat, but I also sincerely doubt you could expand it in time. -350F is seriously cold, and I doubt many are taking into account the material sciences that need to be acquired to have technology continue to operate in such harsh environments.

        The snowshoe idea sound like it has promise, but how many different bird-like tethers would you have to shoot out to suitably spread the weight of the lander over a large enough surface area? Instead of a ball, I'm imagining large feather like tendrils shoot out in all directions with spikes that give it good adhesion to this porous surface. Effectively turning the lander into one huge snowshoe, with the relatively hot lander perhaps being held aloft by it over a melted pit.

        Fun problem to solve :)

        --
        Technically, lunchtime is at any moment. It's just a wave function.
        • (Score: 2) by Immerman on Friday February 02 2018, @09:38PM

          by Immerman (3985) on Friday February 02 2018, @09:38PM (#632173)

          My initial reaction was the same -but the more I think about it, the more I think it could actually be feasible. There's not necessarily any reason the ball has to be inflated during landing - it could potentially be inflated shortly after launch and carried, inflated, across the vast interplanetary distances. Or perhaps not even be inflated, but be some sort of origami snowshoe structure. Point being, if Europa's atmosphere is thin enough to be of little use in aero-braking, and you assume a fully powered landing, then there's no reason you couldn't have a big honking ultralight whatever riding in on the nose, looking like a giant lolipop on a flaming stick.

          Your rocket "stick" would almost certainly melt a hole down into the "cotton candy" crust, but that's fine - don't want your probe on the surface anyway. All the really interesting stuff is going to be under the ice. You just have to release your oversized communication "beach ball" and start paying out your communication tether as you sink below the surface. Cold probably isn't a real problem - I believe most plans call for a nuclear powered probe to melt down through the ice anyway. The real trick is being able to reduce unintentional heat pollution enough to avoid destroying the things you came to study, and thats probably pretty doable. Especially since if there's actually liquid water beneath the ice, and it's not heavily saturated with salts or other chemicals, then at that point you're talking temperatures above 0C anyway.

    • (Score: 2) by DannyB on Friday February 02 2018, @06:52PM

      by DannyB (5839) Subscriber Badge on Friday February 02 2018, @06:52PM (#632102) Journal

      Instead of a balloon, maybe a very large surface area but low density unfoldable footprint which spreads the weight of the lander over a large area.

      --
      When trying to solve a problem don't ask who suffers from the problem, ask who profits from the problem.
    • (Score: 2) by VLM on Friday February 02 2018, @08:08PM

      by VLM (445) on Friday February 02 2018, @08:08PM (#632135)

      The goatse mission plan, yes, familiar with that. It all depends on average particle size. The proverbial Mr Goatse himself was perhaps 50% air if your defined particle size is a cubic meter, but if your particle size is on the scale of a human cell he was either 100% solid human cell or 100% empty air.

      In theory tubgirl could have a very solid pumice stone for scrubbing weight lifting calluses that floats and is mostly air, lower density than quicksand, but it quite solid and can stand on it.

      I guess I'm getting at something like Mr Goatse was mostly air but despite that observed low average density he could support a small vehicle in the air, like a RC car or something, without it sinking thru him.

      The idea of mission planning using memes is intriguing. Despite the highly suggestive name, moonman is likely not of much practical use for lunar missions. And 2G1C is not a long term viable recycling life support system.

  • (Score: 2) by looorg on Friday February 02 2018, @04:04PM (2 children)

    by looorg (578) on Friday February 02 2018, @04:04PM (#632035)

    Will they keep sinking and eventually come out on the other side or will we just have to build them with really long extendable legs? Can we just tie a really big balloon to the lander so it sort of just hovers over the surface and just doesn't really land?

    • (Score: 2) by maxwell demon on Friday February 02 2018, @04:57PM (1 child)

      by maxwell demon (1608) on Friday February 02 2018, @04:57PM (#632052) Journal

      Will they keep sinking and eventually come out on the other side or will we just have to build them with really long extendable legs?

      The nature of gravity together with the nature of friction will ensure that even if the complete moon is made of that porous material, they won't come out at the other side. Rather they will get to rest at the center of the moon. In that case, legs won't help, as there's no ground to stay on.

      --
      The Tao of math: The numbers you can count are not the real numbers.
      • (Score: 3, Funny) by Immerman on Friday February 02 2018, @05:44PM

        by Immerman (3985) on Friday February 02 2018, @05:44PM (#632069)

        Oh ye of little faith - it'll be *surrounded* by ground, we just need to surround it with legs as well, and then it can stand just fine!

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