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In the year 2588, ISRO (Indian Space Research Organization) along with collaboration of NASA had discovered a new planet named Accio several light years farther than Pluto. Scientists have computed following facts after tremendous research:

  1. This planet has almost same configuration of atmosphere composition like that of Moon.
  2. This planet's gravity is exactly same as our Moon.
  3. No trace of life has been observed.

Finally, in 2592, they send a rover to examine the surface characteristics of this planet.

Question: In my story, I want this planet's surface to be completely frictionless. But as mentioned above, this planet has gravity similar to that of the moon. Considering these two facts, what will happen to rover when it lands on the surface?

  1. Will it keep on moving without any energy
  2. Will rover start jumping infinite times
  3. Can rover be able to dig the land and root itself?
  4. How would be the atmospheric configuration near the surface of this planet?
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  • $\begingroup$ I fail to see the relevance of the simulated-worlds tag. Is this a physical or a simulated world? $\endgroup$ – dot_Sp0T Dec 2 '16 at 11:54
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    $\begingroup$ Frictionless doesn't translate into negate friction! Otherwise ur nonstick pan er lander is good to go... $\endgroup$ – user6760 Dec 2 '16 at 11:57
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    $\begingroup$ A new planet... in our solar system? Several light years away from pluto? So a body orbiting our sun that is farther away than alpha centauri? $\endgroup$ – Annonymus Dec 2 '16 at 14:12
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    $\begingroup$ Obligatory xkcd $\endgroup$ – Kys Dec 2 '16 at 15:36
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Even if the surface is frictionless, over time dust and random molecules will land on it due to its gravitational attraction. These won't sit still, they will slide around but remain on the surface at least. Over aeons the dust will form a layer and slow down its movement, eventually creating a more normal surface.

  1. Space dust aside, if the surface was frictionless the rover would continue to move indefinitely without any energy added. Assuming the surface is perfectly flat, of course. If it is uneven the rover may become trapped somewhere, like falling into a hole (as would all the space dust...). It'd still continue to slide around in the bottom of the hole though.

  2. It'll bounce on landing, depending on how rigid and elastic the surface and the rover are, but the vertical motion will settle down eventually as it would elsewhere, friction isn't involved. Any lateral motion will continue (see 1). Any rotational motion around the vertical axis will continue. If the planet is perfectly flat, the result of any landing will leave the rover gliding in one direction, rotating around it's vertical axis. You would need thrusters to dampen this motion, which can only be reduced, not eliminated entirely. A heavy rover with very fine thruster controls might be able to stay approximately still.

  3. Yes, assuming the surface can be penetrated with the rovers tools, as long as they are pushed vertically into it then friction is irrelevant. Rotating drill bits would require thruster/reaction wheel stabilization, as there is nothing stopping the rover from counter-rotating.

  4. The gravity on your planet is not high enough to hold an atmosphere.

Taking a sample on a perfectly flat, hard surface might be difficult. To be able to drill a core sample, the rover needs to hold itself stationary, and push against the surface with the drill. The first can be done with thrusters arranged around the sides of the rover. Pushing against the surface may be difficult though. The Philae lander tried to do this on a comet by using thrusters on the top of the lander, pointing into space, to push it downwards while drilling. In your case, the slightest vertical thrust which isn't exactly through the rovers center of mass will result in an efficient conversion of that thrust into the lander sliding sideways instead (much like pressing your foot at a non-vertical angle onto ice causes a skid). The side thrusters will need to be able to counter this. Any elasticity in the rover body will translate into an erratic skittering on the surface. The side jets need to be designed to handle this, too.

Finally, regarding drilling. I'm not sure how shear forces work in a drill bit, and if friction plays a role in getting the bit to "bite". Maybe frictionless means undrillable, this really needs further development...

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  • $\begingroup$ It might help if you put down two drill bits at the same time, especially if they were rotating in different directions. $\endgroup$ – Peregrine Rook Dec 2 '16 at 20:37
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    $\begingroup$ Predrilling a slightly smaller hole with a laser drill (which wouldn't require force) before trying to drill with a physical bit might help, since drilling doesn't start pulling the drill into a surface until after drill-bit has bitten deep enough to start pulling itself forward. A predrilled hole requires less force to get a bit to 'bite', so less tendency for rover to bounce upward from low gravity. $\endgroup$ – Mark Ripley Dec 3 '16 at 15:25
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It's very difficult to eliminate absolutely all of the friction, just as getting all the way to absolute zero (temperature wise) is harder, the closer you get.

However, you can get very, very close -- especially if your planet is cold. When cold enough, Helium becomes effectively frictionless: https://en.wikipedia.org/wiki/Superfluid_helium-4

Fullerenes are also thought to preferentially collect on cold planetoids; I recall one of the early Man-Kzin war stories using this as a plot device.

Note however that unless your planetoid is just a blob of pure superfluid Helium, there will be some energy dissipation (see rolling friction and/or Hertz contact stresses.) So an unpowered thing in motion will eventually come to a rest with respect to your planet.

Low/no friction will make it difficult to drill or dig, without being bounced away from the surface, even worse if the gravity is low. This has been a problem for the few asteroid landing/sampling missions attempted to date!

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    $\begingroup$ if you push the tool vertically into the surface, then the gravity of the body is the only force on the rover. The surface friction is not relevant, there is no sliding motion, either the tool penetrates, or the rover lifts off into space. A rotating drill bit would not be good on a frictionless surface since the rover would rotate. The asteroid missions had the disadvantage of the gravity being extremely weak, whereas the moons gravity is a lot stronger. The result will depend on the surface, which in this case isn't very realistic to start with. $\endgroup$ – Innovine Dec 2 '16 at 12:52

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