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I am an idiot who doesn't know anything about astronomy, and I always assumed that if you were looking for something like planet 9 you would attempt to deduce i

by fhood 8y ago

I am an idiot who doesn't know anything about astronomy, and I always assumed that if you were looking for something like planet 9 you would attempt to deduce its position from the gravitational effects it might have on nearby known entities. What am I missing in this context?

wolf550e 8y ago
They believe they know where its orbit is because of its gravitational effect on other bodies, but they have no way to know where it currently is along its orbit. Its orbit has between 200 and 1200 times the distance from the Sun as Earth (it's an ellipse), and it takes 10 to 20 thousand years to revolve around the Sun once. Depending on where it is currently on this orbit, it might be that we will need to wait for better technology or for it to plainly get closer to Earth before we can find it.
- vorticalbox 8y ago
  If you know where the other planets are and know the effect 9 plays. Surely you can work out where it will likely be in the sky.
  - wolf550e 8y ago
    It doesn't affect planets, it affects very distant objects and only over long periods of time. https://en.wikipedia.org/wiki/Planet_Nine#/media/File:Planet_Nine_animation.gif https://en.wikipedia.org/wiki/Planet_Nine#/media/File:Planet... https://en.wikipedia.org/wiki/Planet_Nine#Observations:_Orbital_clustering_among_high_perihelion_objects https://en.wikipedia.org/wiki/Planet_Nine#Observations:_Orbi...
aurailious 8y ago
I'd guess there is very few nearby known entities and those that are in the area are too far to be precise enough.
Avshalom 8y ago
Thats how its existence is inferred but there are enough additional bodies that it's a chaotic signal. Then even if you do know where to look that doesn't guarantee you'll spot a relatively small dark object.
badloginagain 8y ago
The article states that's exactly what they're doing. They believe there's a planet nine based on its effect on other objects, and have a theoretical orbital range modeled from those gravitational effects. The problem is space is big, and space is dark, so its hard to find things that don't generate their own light.
- fhood 8y ago
  Ah ok, I guess I just overestimated the level of precision they were working with.
  - fpoling 8y ago
    On the outskirts of Solar system things are far and move slowly. It prevents getting sufficient precision quickly.
  - wongarsu 8y ago
    Even if you could predict the exact orbit, you still don't know where on that orbit it is right now. So even best case that's a lot of space to search.
    - lamellama 8y ago
      It seems like you could predict where it is based on the times the gravitational effects were recorded.
gnarbarian 8y ago
You would. The problem is the gravitational effects are subtle, the planet is very far away, and dim. To add to the problem. Objects in the outer solar system are spread out more vertically in their orbit. ( Like Pluto which dips far above and below the intermediate plane. This means there is a relatively large area of they sky it could be in. Due to it's distance, it is not going to reflect much visible light at all either. So instead of being able to just scan across a the invariable plane looking for it we have to look in a large swath of the sky for something very dim, moving very slowly.
btilly 8y ago
To add to this, they are detecting it based on how it has altered the orbits of other things over a long time, and not based on its direct gravitational effect. Which gives you an idea what its orbit should be, but not where it is within said orbit. That gives them strip of sky to search through. A strip that unfortunately goes past some bright things - like the Milky Way.
tabtab 8y ago
Re: would attempt to deduce its position from the gravitational effects it might have on nearby known entities. What am I missing... There probably are NO "nearby known entities". Planet 9 is probably further away than most detectable objects. The only reason it would possibly be found while "nearby" objects would not is because it's bigger. And it's probably so far away that its gravitational tug is very slight on the big planets that are easy to measure. The article mentioned it may tug the outer gas giants by a "dozen meters" off course from models having no Planet 9 in them. That requires a really powerful "ruler" to detect.

by fhood 8y ago

wolf550e 8y ago

They believe they know where its orbit is because of its gravitational effect on other bodies, but they have no way to know where it currently is along its orbit. Its orbit has between 200 and 1200 times the distance from the Sun as Earth (it's an ellipse), and it takes 10 to 20 thousand years to revolve around the Sun once. Depending on where it is currently on this orbit, it might be that we will need to wait for better technology or for it to plainly get closer to Earth before we can find it.

vorticalbox 8y ago
If you know where the other planets are and know the effect 9 plays. Surely you can work out where it will likely be in the sky.
- wolf550e 8y ago
  It doesn't affect planets, it affects very distant objects and only over long periods of time. https://en.wikipedia.org/wiki/Planet_Nine#/media/File:Planet_Nine_animation.gif https://en.wikipedia.org/wiki/Planet_Nine#/media/File:Planet... https://en.wikipedia.org/wiki/Planet_Nine#Observations:_Orbital_clustering_among_high_perihelion_objects https://en.wikipedia.org/wiki/Planet_Nine#Observations:_Orbi...

aurailious 8y ago

I'd guess there is very few nearby known entities and those that are in the area are too far to be precise enough.

Avshalom 8y ago

Thats how its existence is inferred but there are enough additional bodies that it's a chaotic signal. Then even if you do know where to look that doesn't guarantee you'll spot a relatively small dark object.

badloginagain 8y ago

The article states that's exactly what they're doing. They believe there's a planet nine based on its effect on other objects, and have a theoretical orbital range modeled from those gravitational effects. The problem is space is big, and space is dark, so its hard to find things that don't generate their own light.

fhood 8y ago
Ah ok, I guess I just overestimated the level of precision they were working with.
- fpoling 8y ago
  On the outskirts of Solar system things are far and move slowly. It prevents getting sufficient precision quickly.
- wongarsu 8y ago
  Even if you could predict the exact orbit, you still don't know where on that orbit it is right now. So even best case that's a lot of space to search.
  - lamellama 8y ago
    It seems like you could predict where it is based on the times the gravitational effects were recorded.

gnarbarian 8y ago

You would. The problem is the gravitational effects are subtle, the planet is very far away, and dim. To add to the problem. Objects in the outer solar system are spread out more vertically in their orbit. ( Like Pluto which dips far above and below the intermediate plane. This means there is a relatively large area of they sky it could be in. Due to it's distance, it is not going to reflect much visible light at all either. So instead of being able to just scan across a the invariable plane looking for it we have to look in a large swath of the sky for something very dim, moving very slowly.

btilly 8y ago

To add to this, they are detecting it based on how it has altered the orbits of other things over a long time, and not based on its direct gravitational effect. Which gives you an idea what its orbit should be, but not where it is within said orbit. That gives them strip of sky to search through. A strip that unfortunately goes past some bright things - like the Milky Way.

tabtab 8y ago

Re: would attempt to deduce its position from the gravitational effects it might have on nearby known entities. What am I missing... There probably are NO "nearby known entities". Planet 9 is probably further away than most detectable objects. The only reason it would possibly be found while "nearby" objects would not is because it's bigger. And it's probably so far away that its gravitational tug is very slight on the big planets that are easy to measure. The article mentioned it may tug the outer gas giants by a "dozen meters" off course from models having no Planet 9 in them. That requires a really powerful "ruler" to detect.