Question: could you tell me about the solar system and what the ninth planet could be

Claire Greenwell answered on 8 Mar 2019:

Really far off objects in our solar system are really hard to detect, even though they’re closer than the stars and galaxies we look at. This is because planets are small (in space terms!) and they don’t give off a lot of their own energy. Mostly we rely on seeing the light from the Sun reflected off them. By the time it’s got that far out, reflected, and come back to Earth again, it’s very dim. This is why missions like New Horizons (which passed Pluto a little while ago) are so important – it’s much easier to detect these things from close by. Another way of detecting objects in the Solar system is using their mass – if they are really large, like Jupiter, then they will disturb the orbit of anything near them because of their strong gravity. Some people have noticed small changes in orbits of the outer planets or asteroids that we can see, and think that this means there could be a huge planet orbiting the Sun much further away than any of the known planets. The problem with finding it is that it’s hard to know exactly where to look, which means we need very sensitive telescopes to pick it out from the dark, that can also scan a wide area, which is a difficult engineering challenge. I think that if it’s there it’ll be found in not too many years, which will be exciting.