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Discovery[1]
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| Discovered by | R. S. McMillan Steward Observatory, Kitt Peak (691) |
| Discovery date | December 28, 2005 |
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Designations
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| MPC designation | 2005 YU55 |
| Minor planet category |
PHA[2] Apollo[2] |
| Epoch 2010-Jul-23 (JD 2455400.5) (Uncertainty=1)[2] |
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| Aphelion | 1.6329 AU (Q) |
| Perihelion | 0.65241 AU (q) |
| Semi-major axis | 1.1427 AU (a) |
| Eccentricity | 0.42905 |
| Orbital period | 1.22 yr |
| Mean anomaly | 26.094° (M) |
| Inclination | 0.51351° |
| Longitude of ascending node | 39.304° |
| Argument of perihelion | 268.79° |
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Physical characteristics
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| Dimensions | 310[3]-400 meters[4][5] |
| Sidereal rotation period |
18 hr[2][6] |
| Spectral type | C-type[4] |
| Absolute magnitude (H) | 21.1[2] |
2005 YU55, also written as 2005 YU55, is a potentially hazardous asteroid[2] 310 meters[3] or about 400 m (1,300 feet) in diameter.[4][5] It was discovered on 28 December 2005 by Robert S. McMillan at Steward Observatory, Kitt Peak.[1] On 8 November 2011 it passed 0.85 lunar distances (324,900 kilometers; 201,900 miles)[7] from the Earth. This is the closest known approach by an asteroid with an absolute magnitude this bright since 2010 XC15 (H = 21.4) approached within 0.5 lunar distances in 1976.[6]
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In February 2010, 2005 YU55 was rated 1 on the Torino Scale, indicating that a pass near the Earth is predicted that poses no unusual level of danger. On 19 April 2010, highly accurate radar targeting by the Arecibo radio telescope reduced uncertainties about the orbit by 50%.[5] This improvement eliminated any possibility of an impact with the Earth within the next 100 years.[5] 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.[8]
On 8 November 2011 at 23:28 UT the asteroid safely passed 0.8453 LD (324,900 km; 201,900 mi) from the Earth.[7] On 9 November 2011 at 07:13 UT the asteroid passed 0.6231 LD (239,500 km; 148,800 mi) from the Moon.[9] During the close approach the asteroid reached about apparent magnitude 11,[4][10] 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,[6] observers trying to visually locate the asteroid required a telescope with an aperture of 6 inches (15 centimeters) or larger.[6][7]
The next time a known asteroid this large will come this close to Earth will be in 2028[6] when (153814) 2001 WN5 passes 0.00166 AU (248,000 km; 154,000 mi) from the Earth.[11]
According to Jay Melosh, if an asteroid the size of 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.[12] If an asteroid such as (144898) 2004 VD17 (~580 m across) were to impact land, it would produce a crater about 10 km (6.2 mi) wide and an earthquake of magnitude 7.4.[13] The chances of an actual collision with an asteroid like 2005 YU55 is about 1 percent in the next thousand years.[12]
During the 2011 passage 2005 YU55 has been studied by radar using Goldstone, Arecibo, the Very Long Baseline Array, and the Green Bank Telescope.[6] The Herschel Space Observatory has made far-infrared measurements of 2005 YU55 on November 10, helping determine its temperature and composition.[14]
Radar analysis has also helped to pin down the asteroid's albedo, or diffuse reflectivity. Although radar measurements do not detect visible light they can determine the distance and size of an object with a high degree of accuracy. This information, coupled with visible light measurements, provides a more accurate measure of an object's absolute magnitude, and therefore its albedo.
On November 8, 2011, NASA released a statement mentioning a number of puzzling structures on the surface of the asteroid, which were detected as it passed near the Earth.[15] On November 11, 2011, more refined images provided evidence that these structures are concavities, a ridge near the asteroid's equator, and numerous features that may be large boulders.[16]
On 19 January 2029, 2005 YU55 will pass 0.0023 AU (340,000 km; 210,000 mi) from Venus.[9] The close approach distance to Venus in 2029 determined how close the asteroid will pass the Earth in 2041.[6] Before the November 2011 observations, the uncertainties in the post-2029 trajectory showed that the asteroid would pass somewhere between 0.002 AU (300,000 km; 190,000 mi) and 0.3 AU (45,000,000 km; 28,000,000 mi) of the Earth in 2041.[6] Radar astrometry in November 2011 clarified the Earth passage in 2041 and beyond.[6] As a result of the November 2011 radar observations, it is now known that 2005 YU55 will pass between 0.1017 AU (15,210,000 km; 9,450,000 mi) and 0.1023 AU of the Earth on 12 November 2041.[9] Using the current uncertainty region integrated until the future, the 2075 approach will be between 0.0013 AU (190,000 km; 120,000 mi) and 0.0042 AU (630,000 km; 390,000 mi).[9]
| Preceded by 2010 XC15 |
Large NEO Earth close approach (inside the orbit of the moon) 8 November 2011 |
Succeeded by (153814) 2001 WN5 |
