An asteroid NASA has called "potentially hazardous" was caught whizzing by Earth shortly before Christmas, showing astronomers the dark void at its heart. The Arecibo Observatory in Puerto Rico used its radio telescope to keep an eye on asteroid 3200 Phaethon during its close approach to the planet, creating radar images that revealed new features of the space rock. According to NASA, the asteroid is roughly shaped like a ball and "has a large concavity, or depression, at least several hundred meters in extent near its equator, and a conspicuous dark, circular feature near one of the poles." Arecibo is in an area that was battered by Hurricane Maria earlier this year, and returned to its asteroid-watching activities this month. Astronomers at the Arecibo radio telescope in Puerto Rico took radar images of the large asteroid Phaethon as it passed close to Earth this month.