New dynamical simulations suggest that the mysterious unseen world might be an interstellar rogue that was captured by our solar system.

There are few solar system mysteries quite as compelling as "Planet Nine." The hypothetical world, thought to be orbiting at an extreme distance

By Ian O'Neill seeker.com 1-13-17

from the sun, has some observational evidence that supports its existence. But as it is so far away and therefore so dim, it's not very easy to actually directly observe it.

Calculated to scoot as far away as 1,000 AU from the sun (when 1 AU, or astronomical unit, is the average distance at which the Earth orbits the sun), there's a huge question mark hanging over how it even formed - it had to have evolved far closer to the sun and then some gravitational process migrated it away. This extreme orbit has led to other ideas that Planet Nine might have been pilfered by our sun when it passed close to another star system in the past.

But there's an alternative hypotheses that suggests Planet Nine is actually an alien intruder; a captured "rogue" or orphaned planet that was adopted by the solar system.
Read more »

    A huge alien world orbits 600 billion miles (1 trillion kilometers) from its host star, making its solar system the largest one known, a new study reports.

Astronomers have found the parent star for a gas-giant exoplanet named 2MASS J2126, which was previously thought to be a "rogue" world flying freely through space. The planet and its star are separated by about 7,000 astronomical units (AU), meaning the alien world completes one orbit every 900,000 years or so, researchers said. (One AU is the average distance from Earth to the sun—about 93 million miles, or 150 million km). [...]
Read more »