The Arecibo Observatory Planetary Radar has just released the highest resolution images to date of an asteroid that passed near to Earth. The pictures of 3200 Phaethon during its Dec. 16 flyby show the spherical shape o the asteroid as well as a large concavity near the edge.

The huge asteroid has a diameter of around 3.6 miles, which is significantly larger than previous estimates. NASA classified the asteroid as “potentially hazardous,” and experts believe it would wipe out a city if it were to strike the Earth just right.

The Arecibo Observatory has proven to be a critical tool in monitoring near-Earth asteroids, which has drawn increasing focus in NASA circles. The observatory is based on Puerto Rico and suffered significant damage in the wake of Hurricane Maria, but it has recently returned to full operational service.

“These new observations of Phaethon show it may be similar in shape to asteroid Bennu, the target of NASA’s OSIRIS-REx spacecraft, but more than 1,000 Bennus could fit inside of Phaethon,” said Patrick Taylor, a Universities Space Research Association (USRA), Columbia, Maryland, scientist and group leader for Planetary Radar at Arecibo Observatory. “The dark feature could be a crater or some other topographic depression that did not reflect the radar beam back to Earth.”