Very Close Pass of Asteroid 2005 YU55 November 8-9

UPDATED ELEMENTS NOVEMBER 7!

The followiong is compiled from various NASA reports on this close approach of Asteroid 2005 YU55

On November 8-9, 2011, the Earth-crossing asteroid 2005 YU55 will speed past us at a distance closer than the Moon. With a diameter of about 400 meters, it will be the largest object that's ever been seen passing so close.

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NEW ELEMENTS POSTED NOVEMBER 7

Here are the firm orbital elements for entering into any PC or control program. These are good through the next 24 hours and will result in a very small, if noticeable, offset during the next evening (November 8-9).

These were computed by Bill Gray of ProjectPluto:

Orbital elements:
2005 YU55
Perihelion 2011 Sep 10.258959 TT = 6:12:54 (JD 2455814.758959)
Epoch 2011 Nov 9.0 TT = JDT 2455874.5 Earth MOID: 0.0010 Ve: 0.0003
M 47.53070 (2000.0) Ma: 0.0367
n 0.79561227 Peri. 270.87649 0.62715112 0.77888427
a 1.15345785 Node 37.96499 -0.71164640 0.57537001
e 0.4325850 Incl. 0.42437 -0.31660837 0.24957692
P 1.24/452.47d H 22.1 G 0.15
From 766 observations 2005 Dec. 24-2010 Apr. 20; mean residual 0".437

Asteroid 2005 YU55 was discovered by Spacewatch on December 28, 2005.
It will approach Earth within 0.85 lunar distances (0.00217 AU) on
November 8, 2011, when it will be an extraordinarily strong radar target.
2005 YU55 has an absolute magnitude of 21.9, and imaging at Arecibo in 2010
revealed that the asteroid has a rounded shape with a diameter of about
400 meters.

The 2011 approach is the closest known by an asteroid with an absolute magnitude
this bright since 2010 XC15 (H = 21.4) approached within 0.5 lunar distances in 1976,
and until 2028, when 2001 WN5 (H = 18.2) will approach within 0.65 lunar distances,
and as such, it represents an invaluable scientific opportunity.
We hope to obtain Goldstone images as fine as 2 meters/pixel,
which should reveal a wealth of detail about the asteroid's surface features,
shape, dimensions, and other physical properties

The Arecibo observations in 2010 also revealed that 2005 YU55 has
a rotation period of approximately 18 hours (assuming that the subradar latitude was
close to equatorial); that its circular polarization ratio is about 0.4, indicating a
a moderately rough near-surface compared with other
near-Earth asteroids; that its surface is darker than charcoal at optical wavelengths;
and that it has a relatively bright radar reflectivity of ~20%.

The closest approach occurs just before the date boundary between Nov. 8-9, when 2005 YU55
will move up to 8.6 degrees during the hour between Nov. 8 23:00 - Nov. 9 00:00 UTC.
To place that in perspective, the angular width of the Moon is about 0.5 degrees, so
YU55 will move 17 lunar diameters per hour or about 0.3 lunar diameters per minute.
Motion this rapid will easily be observable in small telescopes with apertures
of roughly 15 cm and larger (at this time the asteroid should reach 11th or 12 magnitude).

2005 YU55 will approach Earth from the direction of the Sun, so it won't
be visible at night until November 8. Afterward, it will move directly away
from Earth, approximately 180 degrees from its approach trajectory.
Radar observations provide their own illumination, so both Goldstone and Arecibo
will be able to observe the asteroid during the day prior to Nov. 9.

2005 YU55 will also be the subject of intensive observations with spectroscopy, photometry,
and infrared radiometry beginning on the night of November 8/9.

The November, 2011 issue of Sky and Telescope magazine features a full-page article on p. 53
that describes the 2011 flyby and provides finder charts for locating the asteroid.

Here is a link to an animation prepared by Jon Giorgini (JPL) that shows the motion
of 2005 YU55 in the vicinity of the Earth and Moon during the flyby:
Flyby Animation

2005 YU55 will also encounter the Moon 8 hours after its flyby with Earth, and somewhat
closer at 0.62 Earth-Moon distances.

This asteroid also closely approaches Venus, most notably within
0.0019 AU (0.74 lunar distances) in 2029. The uncertainties will increase substantially
afterward, so that by the time of the next encounter with Earth in 2046, the asteroid's
minimum distance could be anywhere between 0.002 AU and 0.5 AU.
Radar astrometry obtained in Nov. 2011 should clarify the situation in 2046.

The 2011 encounter is the closest to Earth for at least the last 200 years.

Due to its size and proximity to Earth, the Minor Planet Center has
designated 2005 YU55 as a "Potentially Hazardous Asteroid."
Despite this designation, this object cannot hit Earth during the entire
interval over which its motion can be computed reliably.