8 ms·

NASA finds Neptune moons locked in 'dance of avoidance'

178 points by dnetesn 7y ago

hanniabu 7y ago
It's amazing that we're still discovering stuff like this with large objects in our own solar system. It's humbling and makes me realize how much we still don't know.
- username90 7y ago
  It is nice and all, but these two moons are pretty small, just 30 and 40 km radius. For comparison our moon has a radius of 1700 km.
  - ryan_j_naughton 7y ago
    This is bc our moon is abnormally large. We're almost a binary planet with our moon bc of it's size in comparison to earth.
    - whamlastxmas 7y ago
      I never knew to be thankful that we have a big ol moon in the sky
      - macintux 7y ago
        There’s been speculation, as I recall, that we have the moon to thank for intelligent life. Some references: https://www.scientificamerican.com/article/moon-life-tides/ https://www.scientificamerican.com/article/moon-life-tides/ https://www.npr.org/2011/11/18/142512088/is-a-moon-necessary-for-a-planet-to-support-life https://www.npr.org/2011/11/18/142512088/is-a-moon-necessary...
    - Sharlin 7y ago
      Relative to Earth’s size, sure, but all the giant planets in the solar system have several large spherical moons, hundreds or thousands of km in diameter. These two rocks are small by any planet’s standards.
      - onlyrealcuzzo 7y ago
        Wait. That would mean there are moons twice as big as Earth in our solar system. Jupiter has one that's bigger than Mercury, but still almost 10-times smaller than Earth.
        dmurray 7y ago
        It does not mean that. Mercury is 5,000 km in diameter.
foobarbecue 7y ago
The three body problem is so fun!
jonplackett 7y ago
Is this some kind of mathematical thing based on how orbits work, or is it more like natural selection, in that any moons that don't avoid each other just aren't there anymore.
- FreeFull 7y ago
  It is a mathematical thing based on how orbits work. Orbits that are very close to a resonance but not quite there will tend towards being even closer, so it's a stable system. If this wasn't the case, you wouldn't ever expect to observe anything like this, due to disturbances to the orbits (from other bodies tugging gravitationally on the objects) building up.
  - mirekrusin 7y ago
    Resonance is natural selection.
    - lmilcin 7y ago
      No, it is not. It would be if we saw many colliding orbits and only those that had resonance surviving in long run. But resonances are perfect ratios and no random orbits will ever have perfect ratios of orbit times. Instead what happens is that collisions seem to be extremely rare occurrence. Once two moons find themselves on close orbits they will tend to exchange energy until they find some kind of resonance that will keep true for a very long time until disturbed.
      - mirekrusin 7y ago
        And what is your (absolute offset and) observation timeframe compered to the lifetime of the system?
        lmilcin 7y ago
        There are simulations that show great deal of how and what is the likelihood of different systems forming.
peter303 7y ago
There are now several dozen multiplanet exo-solar systems that exhibit various kinds of resonances. They are a real time laboratory for testing dynamics mathematics.
- devicetray0 7y ago
  > They are a real time laboratory for testing dynamics mathematics. I wouldn't say "testing", but perhaps "observing"?
pmarreck 7y ago
Could survivorship bias be playing a role here? In other words, the moons that did not stabilize in a fashion similar to this either crashed into each other or their planet already a long time ago?
- cwlrs 7y ago
  Well yeah - Masses on a colliding path would have merged over the billions of years. These masses were not, so remain like this
pbosko 7y ago
Could this cause a natural occurrence of resonance cascade?
sk84life5 7y ago
NASA lost all reels about moonwalk ? Oh. What a lies again from NASA
valley-green 7y ago
Yeah sure ‘dance of avoidance’ makes for better clickbait than ‘resonance’, but you sound like a fucking retard. ‘Dance of avoidance’
novelAdTech 7y ago
This is a reversal of cause and effect. We're looking at billion-year-old hydrostatic, spheroid satellites that currently orbit in a system that stabilized a long, long time ago. They are ancient survivors of a chaotic distillation that predates all of life on earth, a dynamic system that stands as a persistent, unchanging choreography, undisturbed in a quiet part of space for eons. None of the bodies are engaging willpower, in order to avoid one another. What scientists are observing just happens to be a closed circuit scale-model racetrack, and the little toy race cars couldn't jump out of their well-worn grooves if they tried. But hey, "science" headlines need clicks too...
tolerate 7y ago
Is hackers news really censoring and deleting comments ?
- dang 7y ago
  No. Why did you think that we might be?
genex 7y ago
“History doesn't repeat itself, but it does rhyme.”
jvanderbot 7y ago
It always amazes me how they dress up the most mundane results (not that all dressed-up results from NASA are mundane!).
chmod775 7y ago
Reminds me of the plot of "Pushing Ice", where a weird moon turns out to be way more than just a piece of rock and ice. https://www.goodreads.com/book/show/89186.Pushing_Ice https://www.goodreads.com/book/show/89186.Pushing_Ice Saturn's moon, Janus, is in a co-orbital configuration with Epimetheus, and... just look at these "orbits": https://upload.wikimedia.org/wikipedia/commons/1/1c/Animation_of_Epimetheus_orbit_-_Rotating_reference_frame.gif https://upload.wikimedia.org/wikipedia/commons/1/1c/Animatio... (Janus in green) The author is an astronomer turned writer, and the stuff he comes up with (or uses in his stories) is always incredibly interesting.
- 205guy 7y ago
  Those are horseshoe orbits in a rotating reference frame (your link does not provide the caption). Janus and Epimetheus do orbit around Saturn elliptically (except when they switch positions) when seen from an inertial frame. https://en.wikipedia.org/wiki/Epimetheus_(moon) https://en.wikipedia.org/wiki/Epimetheus_(moon) https://en.wikipedia.org/wiki/Horseshoe_orbit https://en.wikipedia.org/wiki/Horseshoe_orbit
  - chmod775 7y ago
    I didn't give it much thought what that gif would look like in a vacuum. I should've probably linked to this instead: https://upload.wikimedia.org/wikipedia/commons/f/ff/Epimetheus-Janus_Orbit.png https://upload.wikimedia.org/wikipedia/commons/f/ff/Epimethe... The orbits probably wouldn't look very fancy if you were observing from Saturn (besides the speeding up and slowing down), but when seen from either of the moons, that's roughly what things would seem like to you.
    - chmod775 7y ago
      > The orbits probably wouldn't look very fancy if you were observing from Saturn (besides the speeding up and slowing down) Unless you were moving around the thing at precisely the right velocity I suppose. But it being a gas giant I suppose the point is kind of moot. It's not like you or a manmade device can stand touch down anywhere while still observing the sky.

178 points by dnetesn 7y ago

It's amazing that we're still discovering stuff like this with large objects in our own solar system. It's humbling and makes me realize how much we still don't know.

username90 7y ago
It is nice and all, but these two moons are pretty small, just 30 and 40 km radius. For comparison our moon has a radius of 1700 km.
- ryan_j_naughton 7y ago
  This is bc our moon is abnormally large. We're almost a binary planet with our moon bc of it's size in comparison to earth.
  - whamlastxmas 7y ago
    I never knew to be thankful that we have a big ol moon in the sky
    - macintux 7y ago
      There’s been speculation, as I recall, that we have the moon to thank for intelligent life. Some references: https://www.scientificamerican.com/article/moon-life-tides/ https://www.scientificamerican.com/article/moon-life-tides/ https://www.npr.org/2011/11/18/142512088/is-a-moon-necessary-for-a-planet-to-support-life https://www.npr.org/2011/11/18/142512088/is-a-moon-necessary...
  - Sharlin 7y ago
    Relative to Earth’s size, sure, but all the giant planets in the solar system have several large spherical moons, hundreds or thousands of km in diameter. These two rocks are small by any planet’s standards.
    - onlyrealcuzzo 7y ago
      Wait. That would mean there are moons twice as big as Earth in our solar system. Jupiter has one that's bigger than Mercury, but still almost 10-times smaller than Earth.
      - dmurray 7y ago
        It does not mean that. Mercury is 5,000 km in diameter.

foobarbecue 7y ago

The three body problem is so fun!

jonplackett 7y ago

Is this some kind of mathematical thing based on how orbits work, or is it more like natural selection, in that any moons that don't avoid each other just aren't there anymore.

FreeFull 7y ago
It is a mathematical thing based on how orbits work. Orbits that are very close to a resonance but not quite there will tend towards being even closer, so it's a stable system. If this wasn't the case, you wouldn't ever expect to observe anything like this, due to disturbances to the orbits (from other bodies tugging gravitationally on the objects) building up.
- mirekrusin 7y ago
  Resonance is natural selection.
  - lmilcin 7y ago
    No, it is not. It would be if we saw many colliding orbits and only those that had resonance surviving in long run. But resonances are perfect ratios and no random orbits will ever have perfect ratios of orbit times. Instead what happens is that collisions seem to be extremely rare occurrence. Once two moons find themselves on close orbits they will tend to exchange energy until they find some kind of resonance that will keep true for a very long time until disturbed.
    - mirekrusin 7y ago
      And what is your (absolute offset and) observation timeframe compered to the lifetime of the system?
      - lmilcin 7y ago
        There are simulations that show great deal of how and what is the likelihood of different systems forming.

peter303 7y ago

There are now several dozen multiplanet exo-solar systems that exhibit various kinds of resonances. They are a real time laboratory for testing dynamics mathematics.

devicetray0 7y ago
> They are a real time laboratory for testing dynamics mathematics. I wouldn't say "testing", but perhaps "observing"?

pmarreck 7y ago

Could survivorship bias be playing a role here? In other words, the moons that did not stabilize in a fashion similar to this either crashed into each other or their planet already a long time ago?

cwlrs 7y ago
Well yeah - Masses on a colliding path would have merged over the billions of years. These masses were not, so remain like this

pbosko 7y ago

Could this cause a natural occurrence of resonance cascade?

sk84life5 7y ago

NASA lost all reels about moonwalk ? Oh. What a lies again from NASA

valley-green 7y ago

Yeah sure ‘dance of avoidance’ makes for better clickbait than ‘resonance’, but you sound like a fucking retard. ‘Dance of avoidance’

novelAdTech 7y ago

This is a reversal of cause and effect. We're looking at billion-year-old hydrostatic, spheroid satellites that currently orbit in a system that stabilized a long, long time ago. They are ancient survivors of a chaotic distillation that predates all of life on earth, a dynamic system that stands as a persistent, unchanging choreography, undisturbed in a quiet part of space for eons. None of the bodies are engaging willpower, in order to avoid one another. What scientists are observing just happens to be a closed circuit scale-model racetrack, and the little toy race cars couldn't jump out of their well-worn grooves if they tried. But hey, "science" headlines need clicks too...

tolerate 7y ago

Is hackers news really censoring and deleting comments ?

dang 7y ago
No. Why did you think that we might be?

genex 7y ago

“History doesn't repeat itself, but it does rhyme.”

jvanderbot 7y ago

It always amazes me how they dress up the most mundane results (not that all dressed-up results from NASA are mundane!).

chmod775 7y ago

Reminds me of the plot of "Pushing Ice", where a weird moon turns out to be way more than just a piece of rock and ice. https://www.goodreads.com/book/show/89186.Pushing_Ice https://www.goodreads.com/book/show/89186.Pushing_Ice Saturn's moon, Janus, is in a co-orbital configuration with Epimetheus, and... just look at these "orbits": https://upload.wikimedia.org/wikipedia/commons/1/1c/Animation_of_Epimetheus_orbit_-_Rotating_reference_frame.gif https://upload.wikimedia.org/wikipedia/commons/1/1c/Animatio... (Janus in green) The author is an astronomer turned writer, and the stuff he comes up with (or uses in his stories) is always incredibly interesting.

205guy 7y ago
Those are horseshoe orbits in a rotating reference frame (your link does not provide the caption). Janus and Epimetheus do orbit around Saturn elliptically (except when they switch positions) when seen from an inertial frame. https://en.wikipedia.org/wiki/Epimetheus_(moon) https://en.wikipedia.org/wiki/Epimetheus_(moon) https://en.wikipedia.org/wiki/Horseshoe_orbit https://en.wikipedia.org/wiki/Horseshoe_orbit
- chmod775 7y ago
  I didn't give it much thought what that gif would look like in a vacuum. I should've probably linked to this instead: https://upload.wikimedia.org/wikipedia/commons/f/ff/Epimetheus-Janus_Orbit.png https://upload.wikimedia.org/wikipedia/commons/f/ff/Epimethe... The orbits probably wouldn't look very fancy if you were observing from Saturn (besides the speeding up and slowing down), but when seen from either of the moons, that's roughly what things would seem like to you.
  - chmod775 7y ago
    > The orbits probably wouldn't look very fancy if you were observing from Saturn (besides the speeding up and slowing down) Unless you were moving around the thing at precisely the right velocity I suppose. But it being a gas giant I suppose the point is kind of moot. It's not like you or a manmade device can stand touch down anywhere while still observing the sky.