Asteroid (503941) 2003 UV11 passed by the Earth at a distance of about 5 755 000 km (15.0 times the average distance between the Earth and the Moon, or 3.85% of the distance between the Earth and the Sun), slightly after 3.00 am GMT on Tuesday 31 October 2017. There was no danger of the asteroid hitting us, though were it to do so it would have presented a significant threat. (503941) 2003 UV11 has an estimated equivalent diameter of 240-750 m (i.e. it is estimated that a spherical object with the same volume would be 240-750 m in diameter), and an object at the upper end of this size range would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be 35 000-1 175 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater over 3.8-11 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.
Image of (503941) 2003 UV11 taken on 22 October 2017 using the iTelescope T05 MPC H06 remotely operated telescope at Mayhill Observatory in New Mexico. Image is a composite made of seven 40 second exposures; stars appear elongated as they move across the field, the asteroid is a single spot (indicated by the arrow) as the telescope is being trained on this object. iTelescope/Marian Urbanic/Fotografický občasník.
(503941) 2003 UV11 was discovered on 21 October 2003 by the Lowell Observatory Near-Earth-Object Search, at Anderson Mesa Station, near Flagstaff, Arizona. The designation 2003 UV11 implies that it was the 296th asteroid (asteroid V11) discovered in the second half of October 2003 (period 2003 U), while the designation 503941 implies that it was 503 941st asteroid ever discovered (asteroids are not given this longer designation immediately to avoid naming double or false sightings).
(503941) 2003 UV11 has a 640 day orbital period, with an elliptical orbit tilted at an angle of 5.93° to the plain of the Solar System which takes in to 0.34 AU from the Sun (34% of the distance at which the Earth orbits the Sun; inside the orbit of the planet Mercury) and out to 2.56 AU (256% as far away from the Sun than the Earth). This means that close encounters between the asteroid and Earth are fairly common, with the last thought to have happened in October 2010 and the next predicted in November 2024. It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, (503941) 2003 UV11 is also classified as a Potentially Hazardous Asteroid.
The calculated orbit of (503941) 2003 UV11. Minor Planet Center.
(503941) 2003 UV11 also has frequent close encounters with the planets Mercury, which it is thought to have last passed in September 2012, and is next predicted to pass in December 2024, and Venus, which it last came close to in November 2010 and is next predicted to pass in July 2024. Asteroids which make close passes to multiple planets are considered to be in unstable orbits, and are often eventually knocked out of these orbits by these encounters, either being knocked onto a new, more stable orbit, dropped into the Sun, knocked out of the Solar System or occasionally colliding with a planet.
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