( CNN ) The asteroid that flew close to Earth Monday did n't come alone . NASA images released Monday reveal the asteroid , officially known as 2004 BL86 , has its own small moon . The grainy , black and white photos show the asteroid , about a third of a mile in size , spinning through space , with its 230-foot-wide moon trailing behind . Asteroid 2004 BL86 came about 745,000 miles ( 1.2 million kilometers ) from Earth , or about three times as far away as the moon , just after 11 a.m . ET Monday , according to NASA . It was far enough that it did n't pose a threat to Earth , but close enough to give scientists and amateurs a chance to observe a large asteroid up close . It was the closest known asteroid this large to pass near Earth until 2027 , when an asteroid called 1999 AN10 flies by . Observers on the ground did n't see much when the asteroid was closest to Earth Monday morning , because it was n't at its brightest . Only a portion of its illuminated side was visible , according to Sky & Telescope magazine . The asteroid brightened as it got farther from the Earth because its face became more fully illuminated , the magazine said . The best chance for viewing was from 8 p.m . ET Monday to 1 a.m . ET Tuesday . NASA scientists snapped radar-generated images of the asteroid using the Deep Space Network antenna at Goldstone , California , and the Arecibo Observatory in Puerto Rico . `` While it poses no threat to Earth for the foreseeable future , it 's a relatively close approach by a relatively large asteroid , so it provides us a unique opportunity to observe and learn more , '' Don Yeomans , the recently retired manager of NASA 's Near Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena , California , said in a NASA news release . Yeomans retired on January 9 after 16 years of tracking asteroids . Paul Chodas has been designated as the new manager . `` We should be getting some great radar images of this asteroid , '' Chodas told CNN before the asteroid passed . `` Radar would be the key to study the asteroid 's surface , give an idea of its shape , whether it has rocks and that kind of stuff on it . It 'll be really exciting . '' Observers without binoculars or a scope watched from their computers on The Virtual Telescope Project 2.0 . The asteroid was discovered on January 30 , 2004 , by a telescope of the Lincoln Near-Earth Asteroid Research survey in White Sands , New Mexico . Want to know more about asteroids ? Check out NASA 's asteroid watch program or follow it on Twitter . CNN 's Doug Criss contributed to this story .
The asteroid was its closest on Monday morning , but the best viewing was Monday night . Asteroid 2004 BL86 passed within 750,000 miles of Earth . NASA photos released Monday show small moon orbiting the asteroid .