In February 2010, (308635) 2005 YU55 was rated 1 on the Torino Scale for a potential pass near Earth on November 10, 2103, that posed no unusual level of danger. On 19 April 2010, radar ranging by the Arecibo radio telescope reduced uncertainties about the orbit by 50%. This improvement eliminated any possibility of an impact with Earth within the next 100 years. It was removed from the Sentry Risk Table on 22 April 2010 and as such it now has a rating of 0 on the Torino Scale. It is now known that on 10 November 2103 (308635) 2005 YU55 will be roughly 2 AU from Earth.
On 8 November 2011 at 23:28 UT the asteroid passed 0.85 LD (330,000 km; 200,000 mi) from Earth. On 9 November 2011 at 07:13 UT the asteroid passed 0.6231 LD (239,500 km; 148,800 mi) from the Moon. During the close approach the asteroid reached about apparent magnitude 11, and would have been visible to experienced observers using high-end binoculars with an objective lens of 80+ mm if it were not for bright moonlight preventing a true dark sky. Since the gibbous moon did interfere with the viewing, observers trying to visually locate the asteroid required a telescope with an aperture of 6 inches (15 centimeters) or larger.
The next few times a known asteroid this large will come this close to Earth will be in 2028 when (153814) 2001 WN5 passes 0.65 LD from Earth, and in 2029 when the 325-meter 99942 Apophis comes even closer at just 0.10 LD.
According to Jay Melosh, if an asteroid the size of (308635) 2005 YU55 (~400 m across) were to hit land, it would create a crater 6.3 km (3.9 mi) across, 518 m (1,699 ft) deep and generate a seven-magnitude-equivalent-earthquake. The chances of an actual collision with an asteroid like (308635) 2005 YU55 is about 1 percent in the next thousand years.
During the 2011 passage (308635) 2005 YU55 was studied with radar using Goldstone, Arecibo, the Very Long Baseline Array, and the Green Bank Telescope. The Herschel Space Observatory has made far-infrared measurements of (308635) 2005 YU55 on November 10, helping determine its temperature and composition.