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TorontoCorsair t1_jd5fk2c wrote

Reply to comment by UrsusRomanus in Is there another massive planet beyond Neptune? If so, why haven’t we found it? by Always2ndB3ST

This.

Exoplanet hunting is significantly easier because of this. We also know where to look because each star acts as a beacon indicating that there may be planets and the field of view required for detection is minimal. We don't really need to calculate where they may be, we just have to observe in one small spot of the sky for a bit of time and see if the brightness level changes.

Trying to detect another planet around our own sun we could potentially calculate for, but even trying to observe it may be incredibly difficult as it could be a very dark object that doesn't radiate much of anything and if it is passed neptune it is barely receiving any light from our sun. Add in that it technically could be anywhere within sky, more realistically within the 17 degrees all other planets of the sky are within, we still would have to look over huge swaths of the sky to try and find it. A most difficult task indeed.

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sifuyee t1_jd5h5q4 wrote

And most of the Exoplanets are actually found by observing the small doppler (color) shift of the parent star light as the planet tugs the star towards us then away from us, which is why most of the planets found so far are close to their parent stars (means we can find the color/doppler shift with shorter observation times). Since this object would be beyond the orbit of Neptune, its orbit period is longer, thus one would have to make very precise observations over baselines of a century or so to see the signal start to show up in solar observations. We might just be getting close to that threshold now though if someone wanted to try to compile the last century of data and try to correct for all the instrument bias and other sources from the rest of the known solar system. That would only give us the general orbit period and distance though.

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