OUR SOLAR SYSTEM HAS A NINTH PLANET

摘要

Dwarf planets are a dime a dozen. When it comes to real planets-bodies with enough mass to achieve a nearly round shape, clear nearby debris, and orbit the sun-we know of only eight in our solar system. Over the past century, many astronomers claimed to have caught whiff of an elusive ninth body: Planet X. The latest to make this assertion is the same man who demoted Pluto. "We've found evidence of a giant planet in the outer solar system," says Mike Brown, an astronomer at the California Institute of Technology. "By 'giant,' I mean the size of Neptune, and by 'outer solar system,' I mean 10 to 20 times farther away than Pluto."