4 ms·

Is it fair to say it is easier to detect planets in other solar systems?

bastawhiz 3y ago
Yes! We often detect planets in other solar systems because they pass in front of their stars, causing the brightness to dip. You can also look for Doppler shifts in the light you see from stars, which is caused by the planet pulling the star slightly. You can also look for the sorts of brightness changes you'd expect as a result of gravity lensing. In almost all cases, you're looking for changes in something you can already see. The problem with a planet 9 is that so little light is getting to it that it's going to be very very dim.
- greggsy 3y ago
  Wouldn’t it still be passing in front of something, or is it likely to be comparatively ‘stationary’ against a similarly stationary backdrop of stars and other objects?
  - bastawhiz 3y ago
    When a star is occluded by a planet, it'll dip in brightness at a pretty regular interval (because of the orbit). So you can look look for a series of dips, which gives you a candidate. That's then looked at more closely. Since a planet 9 wouldn't transit a star at any regular interval, it wouldn't show up as a candidate for that search technique.
    - catlifeonmars 3y ago
      So we would need to potentially deliver the telescope far outside of our solar system and have it look back at us, kind of like a very expensive selfie stick?
      - bastawhiz 3y ago
        That's not possible. The furthest things we've ever sent out are the voyager probes, and they're 135 and 162au away, each. We'd have to get twice that distance to even be at the distance that we expect a planet 9 to be. Even if we managed to get many multiples of the distance planet 9 is from the sun to take pictures backward and send them home to earth, it's _so far_ from the sun that a) the amount it would occlude the sun is ridiculously small, if it ever even lined up. At that distance, the sun just looks like another star in the sky. That's like waiting for one particular asteroid to block out the North Star. And b) the orbit period would still need to be short enough that you could see it transit a few times to use the technique that scientists use to detect planets elsewhere. Just seeing something block the sun doesn't tell you what it was that blocked it, especially at 400-800au distance. Plus, then you're talking about latencies of about a light month, which makes it super hard to even know to look for the thing you saw (a month ago).

Yes! We often detect planets in other solar systems because they pass in front of their stars, causing the brightness to dip. You can also look for Doppler shifts in the light you see from stars, which is caused by the planet pulling the star slightly. You can also look for the sorts of brightness changes you'd expect as a result of gravity lensing. In almost all cases, you're looking for changes in something you can already see. The problem with a planet 9 is that so little light is getting to it that it's going to be very very dim.

greggsy 3y ago
Wouldn’t it still be passing in front of something, or is it likely to be comparatively ‘stationary’ against a similarly stationary backdrop of stars and other objects?
- bastawhiz 3y ago
  When a star is occluded by a planet, it'll dip in brightness at a pretty regular interval (because of the orbit). So you can look look for a series of dips, which gives you a candidate. That's then looked at more closely. Since a planet 9 wouldn't transit a star at any regular interval, it wouldn't show up as a candidate for that search technique.
  - catlifeonmars 3y ago
    So we would need to potentially deliver the telescope far outside of our solar system and have it look back at us, kind of like a very expensive selfie stick?
    - bastawhiz 3y ago
      That's not possible. The furthest things we've ever sent out are the voyager probes, and they're 135 and 162au away, each. We'd have to get twice that distance to even be at the distance that we expect a planet 9 to be. Even if we managed to get many multiples of the distance planet 9 is from the sun to take pictures backward and send them home to earth, it's _so far_ from the sun that a) the amount it would occlude the sun is ridiculously small, if it ever even lined up. At that distance, the sun just looks like another star in the sky. That's like waiting for one particular asteroid to block out the North Star. And b) the orbit period would still need to be short enough that you could see it transit a few times to use the technique that scientists use to detect planets elsewhere. Just seeing something block the sun doesn't tell you what it was that blocked it, especially at 400-800au distance. Plus, then you're talking about latencies of about a light month, which makes it super hard to even know to look for the thing you saw (a month ago).