All sorts of excitement accompanied astronomers' discovery of Gliese 581g in 2010—the alien world looked like Earth in both size and temperature, and thus seemed potentially hospitable to life.
The supermassive black hole is 40 million times as massive as the sun and powers a quasar that existed 700 million years after the Big Bang.
The asteroid zoomed by Earth at a perfectly safe distance of around 1.8 million miles (2.9 kilometers).
Images show surprise changes to the spacecraft as it interacted with the atmosphere.
