Re: [math-fun] Lots of smaller 'Ronin' (sun-less/ejecta) planets
hbaker1 <hbaker1@pipeline.com> wrote:
FYI -- And we thought that Earth's orbits were getting full of space junk...
I can envision 'Star Trek'-like starships ending up like windshield- splatted bugs in picoseconds...
"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." -- Douglas Adams A collision in interplanetary space is extremely unlikely. James White wrote a novel titled _Deadly Litter_, in which littering in space is a serious crime, since a collision at interplanetary speeds with a single discard coffee ground would wreck a spaceship. I did the math. Collisions in low Earth orbit are an issue, Collisions in interplanetary space are not. If I recall correctly, I determined that if every person who ever lived had a spaceship and traveled at random in the solar system, spending all their time tossing coffee grounds overboard, and kept doing so until the sun turned into a red giant in a few billion years, there would probably not be a single collision. This was partly because the speeds all exceeded solar system escape velocity, so the litter wouldn't accumulate. Debris in the asteroid belt would be a much bigger concern, since there's more of it and since it doesn't dissipate. But even though there are trillions of unmapped objects there big enough to destroy any space probe, not one of the probes that's been sent through the belt has been damaged, and probably none ever will. And the "ronin" planets aren't in interplanetary space, but in interstellar space, which is a couple dozen orders of magnitude larger. A chance collision in interstellar space, even with a grain of sand, is absurdly unlikely. If there was much stuff there, we couldn't see very far, but in most directions we can see all the way to the cosmic horizon. Mankind has sent five probes into interstellar space. (Whether any of them have reached it yet depends on your definition, but they'll all get there eventually.) It's interesting to think about how any of them could be someday detected by aliens, or, conversely, how our own remote descendants could ever detect similar probes from other solar systems. Suppose every one of the ~10^11 stars launched, over its lifetime, a thousand Voyager-like probes into random interstellar trajectories, all of which will forever remain within the galaxy. How would an advanced civilization go about finding any of them? (Not counting ones that had been launched in the past thousand years or so, hence were still close to their parent star.) Unless there's some completely unknown science, the best way seems to be radar. To have a reasonable chance of success, most of the mass of the galaxy would have to be turned into search ships, and every one of them would have to have a radar so powerful that not only would we have already picked it up if it was operating anywhere in the universe in our past light cone, Marconi would have picked it up too.
A handful of free-floating planetary-mass objects have been discovered by infrared surveys of young stellar clusters and star-forming regions as well as wide-field surveys, but these studies are incomplete for objects below five Jupiter masses.
I'd bet that those studies are incomplete for objects above five Jupiter masses, too. What would it be like on a Earth-sized planet far from any star? The obvious answer is "cold and dark." But what if the planet was somehow traveling fast enough that the cosmic microwave background's flux was equal to the sun's flux on our planet? That would be very close to the speed of light. I haven't gotten around to working out what the spectrum of the resulting light would be like. What would its color temperature be? And how wide a visible spot in the sky? Also, how long would it last before it was dimmed either by drag from the light slowing the planet or by cosmic expansion dropping the microwave background's temperature? I expect the latter would get you first, due to the enormous time dilation. And what are the chances of a collision with something? Probably quite small despite the absurd velocity, since even if you didn't start in intergalactic space, you'd end up there pretty quickly and almost certainly remain there forever. (Choose a random direction in space. Chances are the first galaxy in that direction, if any, is so distant that it will have gone past the cosmic horizon long before anything from here could reach it.) Suppose the planet continued to accelerate just enough to counteract the dimming due to cosmic expansion. Could that go on forever? Or would the required acceleration reach infinity as the microwave background asymptotically approaches absolute zero? Remember that half the temperature means 1/16th the flux, all else being equal, and that the temperature is dropping faster than inversely proportional to the age of the universe due to dark energy and accelerating expansion. Finally, what would such a planet look like to us? How far away could we see it? If it was headed roughly toward us, the reflected light would be blue shifted again, and would be enormously bright. Its proper motion would be ridiculously high, since its speed would barely lag the light we're seeing it by.
Yes, space is big, and collisions are incredibly unlikely. Yet we don't really know how much (small, dark) junk there is out there, so it's difficult to compute any probabilities. Maybe there's enough to account for "dark" matter. :-) :-) Re Gosper's comment on 2D v. 3D & the 3-body problem: I don't know the probability distributions for the 3-body problem in 3D (does anyone have any links?) but the vast majority of our solar system (and everyone else's solar systems) are basically 2D systems. Either the non-2D stuff got corralled into the ecliptic, or it got ejected. Re the lack of Ronin Jupiters: Duh! It's the Jupiters of solar systems that do the kicking, when stuff gets kicked out, so it makes sense that most of these Ronins would be smaller than Jupiters. At 08:10 PM 7/26/2017, Keith F. Lynch wrote:
hbaker1 <hbaker1@pipeline.com> wrote:
FYI -- And we thought that Earth's orbits were getting full of space junk...
I can envision 'Star Trek'-like starships ending up like windshield- splatted bugs in picoseconds...
"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." -- Douglas Adams
A collision in interplanetary space is extremely unlikely. James White wrote a novel titled _Deadly Litter_, in which littering in space is a serious crime, since a collision at interplanetary speeds with a single discard coffee ground would wreck a spaceship.
I did the math. Collisions in low Earth orbit are an issue, Collisions in interplanetary space are not. If I recall correctly, I determined that if every person who ever lived had a spaceship and traveled at random in the solar system, spending all their time tossing coffee grounds overboard, and kept doing so until the sun turned into a red giant in a few billion years, there would probably not be a single collision. This was partly because the speeds all exceeded solar system escape velocity, so the litter wouldn't accumulate. Debris in the asteroid belt would be a much bigger concern, since there's more of it and since it doesn't dissipate. But even though there are trillions of unmapped objects there big enough to destroy any space probe, not one of the probes that's been sent through the belt has been damaged, and probably none ever will.
And the "ronin" planets aren't in interplanetary space, but in interstellar space, which is a couple dozen orders of magnitude larger. A chance collision in interstellar space, even with a grain of sand, is absurdly unlikely. If there was much stuff there, we couldn't see very far, but in most directions we can see all the way to the cosmic horizon.
Mankind has sent five probes into interstellar space. (Whether any of them have reached it yet depends on your definition, but they'll all get there eventually.) It's interesting to think about how any of them could be someday detected by aliens, or, conversely, how our own remote descendants could ever detect similar probes from other solar systems. Suppose every one of the ~10^11 stars launched, over its lifetime, a thousand Voyager-like probes into random interstellar trajectories, all of which will forever remain within the galaxy. How would an advanced civilization go about finding any of them? (Not counting ones that had been launched in the past thousand years or so, hence were still close to their parent star.)
Unless there's some completely unknown science, the best way seems to be radar. To have a reasonable chance of success, most of the mass of the galaxy would have to be turned into search ships, and every one of them would have to have a radar so powerful that not only would we have already picked it up if it was operating anywhere in the universe in our past light cone, Marconi would have picked it up too.
A handful of free-floating planetary-mass objects have been discovered by infrared surveys of young stellar clusters and star-forming regions as well as wide-field surveys, but these studies are incomplete for objects below five Jupiter masses.
I'd bet that those studies are incomplete for objects above five Jupiter masses, too.
What would it be like on a Earth-sized planet far from any star? The obvious answer is "cold and dark." But what if the planet was somehow traveling fast enough that the cosmic microwave background's flux was equal to the sun's flux on our planet? That would be very close to the speed of light. I haven't gotten around to working out what the spectrum of the resulting light would be like. What would its color temperature be? And how wide a visible spot in the sky?
Also, how long would it last before it was dimmed either by drag from the light slowing the planet or by cosmic expansion dropping the microwave background's temperature? I expect the latter would get you first, due to the enormous time dilation. And what are the chances of a collision with something? Probably quite small despite the absurd velocity, since even if you didn't start in intergalactic space, you'd end up there pretty quickly and almost certainly remain there forever. (Choose a random direction in space. Chances are the first galaxy in that direction, if any, is so distant that it will have gone past the cosmic horizon long before anything from here could reach it.)
Suppose the planet continued to accelerate just enough to counteract the dimming due to cosmic expansion. Could that go on forever? Or would the required acceleration reach infinity as the microwave background asymptotically approaches absolute zero? Remember that half the temperature means 1/16th the flux, all else being equal, and that the temperature is dropping faster than inversely proportional to the age of the universe due to dark energy and accelerating expansion.
Finally, what would such a planet look like to us? How far away could we see it? If it was headed roughly toward us, the reflected light would be blue shifted again, and would be enormously bright. Its proper motion would be ridiculously high, since its speed would barely lag the light we're seeing it by.
participants (2)
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Henry Baker -
Keith F. Lynch