MARK GARLICK / SCIENCE PHOTO LIBRARY
BILLIONS of years ago, there may have been two suns in our solar system. If so, that could explain how the solar system caught its outermost objects, including the hypothetical Planet Nine.
Our solar system is far bigger than just the space occupied by the eight official planets: it extends out to the Oort cloud, a belt of icy objects that sits about 2000 to 100,000 times as far from the sun as Earth does, and is only loosely gravitationally bound to the sun.
How …