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A nomadic tribe exists deep in the vastness of space, calling a rogue celestial object home. Their Skywatchers have seen another lonely object that will cross paths with theirs, so they begin preparation for a great exodus from their home planet. This is their species' tenth exodus, to which legend gave them the name Planet Walkers.

If two celestial objects cross paths close enough, could a creature jump between them and survive?

Austin A
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    Celestial objects are likely to pass each other with relative speeds in km/s. No complex organism is known to be able to survive such impact. – Alexander Jan 12 '18 at 23:16
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    Jump? Hell no. Getting two planet sized objects that close together would be a disaster for one, if not both, of them. The Roche Limit for Earth is six million meters. And that's ignoring the speed problem Alexander brings up. – Draco18s no longer trusts SE Jan 12 '18 at 23:17
  • That's why I said 'celestial object', it doesn't have to be as big as a planet. Also for sake of not being killjoys, we can assume the (unlikely) scenario that the objects aren't crossing with that much difference in relative speed. – Austin A Jan 12 '18 at 23:20
  • The use of the word planet was just for the sake of a cool name. – Austin A Jan 12 '18 at 23:22
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    "The objects aren't crossing with that much difference in relative speed": then they would collapse one onto the other. That man Newton surely was heartless; his so-called "law" of universal gravitation is always ready to pounce on unsuspecting celestial objects. – AlexP Jan 12 '18 at 23:34
  • Fair point for objects of non-negligible gravity. – Austin A Jan 13 '18 at 00:25
  • Something smaller than a planet won't help you. The Roche limit is independent of size. It's a matter of distance and density. The 6 million meter figure he gave is for typical rocky bodies. An asteroid that passes closer than that breaks up. – Loren Pechtel Jan 13 '18 at 05:28
  • The Roche limit is absolutely dependent on size, as size is a factor in the structural integrity an object that allows it to survive the tidal forces. By the way, the 6 million meter figure @Draco18s quoted: that's the radius of the Earth... Please fact check something before you compound the problem with more wild conjectures. – Austin A Jan 13 '18 at 07:49
  • Correction: size is a factor in the magnitude of the tidal forces exerted on an object. – Austin A Jan 13 '18 at 07:56
  • @AustinA It's approximately 6 million kilometers from the surface of the Earth--which is the number you would be looking at for how far someone would have to jump. And I meant size doesn't matter for the body being destroyed (except bigger bodies are normally denser and can get closer before being destroyed)--of course the size of the bigger body matters! – Loren Pechtel Jan 13 '18 at 15:53
  • The "6 million meter" (not kilometer) figure that you're quoting comes from a table that is prefaced with: "The table below shows the mean density and the equatorial radius* for selected objects in the Solar System*". – Austin A Jan 16 '18 at 00:59
  • Here's another table you can compare with – Austin A Jan 16 '18 at 01:03

3 Answers3

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Stepping back a bit to make this possible...

  • The rogue celestial objects are not planets. They are asteroids.
  • The "Planet Walkers" live inside this asteroid.
  • The lack of atmosphere or magnetic fields on asteroids mean that they can accrue a large electrical charge from the solar wind.
  • Creative use of the electrical phenomena around asteroids will put some space between the shenanigans of the planet walkers and cruel Newtonian physics, and make for fun and engaging fiction.

https://www.nasa.gov/content/goddard/new-nasa-model-gives-glimpse-into-the-invisible-world-of-electric-asteroids/

"For example, understanding the electrical environment around an asteroid could help identify locations where astronauts can safely make first contact with the object," said co-author William Farrell of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "If an astronaut is tethered to a spacecraft that is in sunlight and positively charged, and touches a negatively charged asteroid surface in shadow, there could be an unexpected current flow between the two systems upon contact. We simply can't speculate on the nature of that current without this model."

The electrical charge on asteroids can produce attraction or repulsion through empty space, and be strong enough to overcome the pull of gravity. One can even see this on earth, where static electricity can pull an object up off the ground. In dry airless space static charges can become very large.

NASA has a scheme for an "E-glider" - a spacecraft which makes use of these electrostatic forces around asteroids to maneuver.

https://www.nasa.gov/feature/e-glider-active-electrostatic-flight-for-airless-body-exploration

E-glider

So in this scenario, the Planet Walkers manipulate electrostatic forces as artificial gravity on their low-mass asteroid. These same electrostatic forces are what allows a near miss between their home and their new destination - as they closely approach they repel each other. The Planet Walkers use the near miss to make their jump and by altering the electrical charge on their own bodies, are reeled in by the departing lonely object.

Willk
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  • That sounds pretty cool, maybe this species could exist in an asteroid belt orbiting a sun. +1 for creativity! – Austin A Jan 14 '18 at 05:28
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Nope.

As others have commented, two objects large enough to have significant gravity will either destroy each other or become one large blob (in a cataclysmic event) when they get anywhere near each other.

If the objects are small, like 2 asteroids, they won't tear each other apart. However, asteroids don't have atmosphere, which makes life impossible (as far as we know). Also, the meager gravity would give your creatures the tendency to float off into space and die if they didn't hold on all the time.

BrettFromLA
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  • Good points; however, I wonder if there is a sweet spot for two medium-sized objects? – Austin A Jan 13 '18 at 00:32
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    Rather the opposite of a sweet spot - any object barely massive enough to hold an atmosphere (and inhabitats) is already far too massive for a close approach that is non-destructive. – user535733 Jan 13 '18 at 15:43
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No, if the objects are sufficiently close and moving at a relative speed in relation to each other that would make a jump survivable, gravity would either make them collide or send them into an eventual collision.

If moving fast enough that velocity is sufficiently greater than the gravitational forces to keep moving without being trapped or colliding, then the jump would not be survivable.

However your people have already done this successfully 9 times, so they can counter this problem with their technology. I'm thinking along the lines of using magnetic forces somehow to make it feasible, but the details are beyond what we can do.

Kilisi
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