3 ms·

What sort of speed might some of these rogue planets be moving at? While the faster they move, the harder it would be to 'latch on' to a stable orbit / land, co

What sort of speed might some of these rogue planets be moving at? While the faster they move, the harder it would be to 'latch on' to a stable orbit / land, could they more than a waypoint to distant stars - might they be a 'spaceship'? Although this would require us to 1) discover a dark planet, 2) moving at an appreciable percent of lightspeed, 3) with enough time to reach it, and 4) heading in the right direction so we could alight at a nearby solar system. If colonization sounds hard, how about those hitchhiking odds - infinitely improbable!

jessriedel 12y ago
No, there shouldn't be any rouge planets moving fast enough. Stars at our distance from the galactic center move at roughly 230 km/s, with relative speeds of 10-30 km/s. The escape velocity from the galaxy is ~550 km/s, which is something like 0.2% light speed. Very few objects get accelerated above this speed, and when they do they leave the galaxy (so the probability that we pass one going by is negligible).
- sdrothrock 12y ago
  > No, there shouldn't be any rouge planets moving fast enough. For comparison's sake, the only rouge planet that we know of is Mars, which moves around 24 km/s. :)
  - sova 12y ago
    24 km/s relative to whom/what? =)
  - mirimir 12y ago
    The discovery of hypervelocity stars (HVS) leaving our galaxy with speeds of nearly $10^{3}$ km s$^{-1}$ has provided strong evidence towards the existence of a massive compact object at the galaxy's center. HVS ejected via the disruption of stellar binaries can occasionally yield a star with $v_{\infty} \lesssim 10^4$ km s$^{-1}$, here we show that this mechanism can be extended to massive black hole (MBH) mergers, where the secondary star is replaced by a MBH with mass $M_2 \gtrsim 10^5 M_{\odot}$. We find that stars that are originally bound to the secondary MBH are frequently ejected with $v_{\infty} > 10^4$ km s$^{-1}$, and occasionally with velocities $\sim 10^5$ km s$^{-1}$ (one third the speed of light), for this reason we refer to stars ejected from these systems as "semi-relativistic" hypervelocity stars (SHS). http://arxiv.org/abs/1411.5022 http://arxiv.org/abs/1411.5022 There could also be hypervelocity planets, right? Catching up to them would be hard, though.
    - jessriedel 12y ago
      > There could also be hypervelocity planets, right? There could definitely be hypervelocity planets just like planets. However, the density of these drops dramatically as you increase the speed you're looking for above the "typical" speed at our galactic radius (~230 km/s), simply because they are created by chance events. I believe the density of rouge planets is supposed to be of order the average density of normal planets in the galaxy (i.e., there might be 3 times as many rouge planets, but not 100 times as many). So finding a relativistic rouge planet nearby enough to be useful has negligible probability. (They are created by close encounters with black holes, after all.) > Catching up to them would be hard, though. Well, if you're thinking about using them as "space ships", you need to get up to speed anyways (since the alternative is to just travel on your own).
      - mirimir 12y ago
        Yes, that's a good point about density. If you could catch one, your itinerant colony would have resources at speed for interstellar travel. You'd only need to accelerate a relatively small ship. And those resources would include mass for decelerating your ship at destination. But you couldn't stop for very long, without losing your ride.

jessriedel 12y ago

No, there shouldn't be any rouge planets moving fast enough. Stars at our distance from the galactic center move at roughly 230 km/s, with relative speeds of 10-30 km/s. The escape velocity from the galaxy is ~550 km/s, which is something like 0.2% light speed. Very few objects get accelerated above this speed, and when they do they leave the galaxy (so the probability that we pass one going by is negligible).

sdrothrock 12y ago
> No, there shouldn't be any rouge planets moving fast enough. For comparison's sake, the only rouge planet that we know of is Mars, which moves around 24 km/s. :)
- sova 12y ago
  24 km/s relative to whom/what? =)
- mirimir 12y ago
  The discovery of hypervelocity stars (HVS) leaving our galaxy with speeds of nearly $10^{3}$ km s$^{-1}$ has provided strong evidence towards the existence of a massive compact object at the galaxy's center. HVS ejected via the disruption of stellar binaries can occasionally yield a star with $v_{\infty} \lesssim 10^4$ km s$^{-1}$, here we show that this mechanism can be extended to massive black hole (MBH) mergers, where the secondary star is replaced by a MBH with mass $M_2 \gtrsim 10^5 M_{\odot}$. We find that stars that are originally bound to the secondary MBH are frequently ejected with $v_{\infty} > 10^4$ km s$^{-1}$, and occasionally with velocities $\sim 10^5$ km s$^{-1}$ (one third the speed of light), for this reason we refer to stars ejected from these systems as "semi-relativistic" hypervelocity stars (SHS). http://arxiv.org/abs/1411.5022 http://arxiv.org/abs/1411.5022 There could also be hypervelocity planets, right? Catching up to them would be hard, though.
  - jessriedel 12y ago
    > There could also be hypervelocity planets, right? There could definitely be hypervelocity planets just like planets. However, the density of these drops dramatically as you increase the speed you're looking for above the "typical" speed at our galactic radius (~230 km/s), simply because they are created by chance events. I believe the density of rouge planets is supposed to be of order the average density of normal planets in the galaxy (i.e., there might be 3 times as many rouge planets, but not 100 times as many). So finding a relativistic rouge planet nearby enough to be useful has negligible probability. (They are created by close encounters with black holes, after all.) > Catching up to them would be hard, though. Well, if you're thinking about using them as "space ships", you need to get up to speed anyways (since the alternative is to just travel on your own).
    - mirimir 12y ago
      Yes, that's a good point about density. If you could catch one, your itinerant colony would have resources at speed for interstellar travel. You'd only need to accelerate a relatively small ship. And those resources would include mass for decelerating your ship at destination. But you couldn't stop for very long, without losing your ride.