Exiled to the solar system's edge

摘要

Our solar system might not be the weird kid on the block after all. Astronomers announced on 20 January that they have strong evidence for a planet around 10 times Earth's mass lurking unseen in the outer solar system. If it bears out, this world would fill a hole in our solar system's family tree: a missing super-Earth. Super-Earths, also known as mini-Neptunes since they may be gassy or rocky, are among the most common planets in the Milky Way. Hundreds have been spotted in other solar systems over the past 20 years, but there appeared to be none at home.