Hidden Pluto

Pluto is about forty times the distance from the Sun as Earth. But our Solar System is over 50000 times across that which means it could be hiding some huge blackbody.

In recent years, astronomers have discovered a bunch of planets located at least 100 astronomical units away from their host stars. These planets are gas giants. The problem is that they dont emit light well unless they are close to something bright like the sun. This is something very different the dwarf planets like Pluto and Eris discovered in our solar system's Kuiper Belt and beyond.

There's almost no chance that these giant planets could have formed as part of their host star's planetary disc, considering their immense distance away. That strongly suggests that these are former rogue planets captured by the star's gravity. Scientists at Harvard-Smithsonian Center and Peking University's Kavli Institute tries to figure out just how often we can expect stars; potentially including those like our own Sun; to capture these giant wandering planets.

Quoted by ScienceNOW report:

"Because most stars are born with others, Perets and Kouwenhoven ran computer simulations to see what happens when a star cluster contains free-floating planets. If the number of free-floating planets equals the number of stars, then 3% to 6% of the stars succeed in capturing a planet, and some stars capture two or three. Most of the captured planets end up hundreds or thousands of times farther from their stars than Earth is from the sun. Furthermore, most captured planets have orbits tilted to those of native-born planets, and half the captured planets revolve around their stars backward."

Their work depends on having a good grasp of how many rogue planets there really are, and we can't be sure our current estimates, which suggest there area as many wandering planets as there are stars, is accurate. But if these results are accurate, then our Sun, whose mass is slightly above average, had a real chance of capturing one or more planets eons ago.

The chances aren't huge but probably only a few percent higher. If their numbers are accurate, then the possibility of such a planet definitely exists.