Asteroid 2005 YU55 was discovered in late 2005 (duh!) by Bob McMillan and Jim Scotti of Spacewatch, at the Lunar and Planetary Lab within the University of Arizona. Once the orbit was refined thanks to continued observations it became clear 2005 YU55 would not hit the Earth…though it would pass near. In a few weeks, late on November 8 (UTC), 2005 YU55 will fly by the Earth and Moon and continue, barely perturbed, on its 446 day orbit around the Sun.
Its closest approach of 325,162 km (202,089 miles) will take place around 23:29 UTC (18:29 ET). A few hours later, on the morning of November 9 at around 07:20 UTC (02:20 ET), it will whiz by even closer to the Moon, at a distance of some 239,867 km (149,078 miles). Thanks to Arecibo’s radar telescope (see image above) we now know this asteroid is roughly spherical in shape with a diameter of about 400m (1311 feet); that’s slightly less than 4 football fields (American or European) end to end. Good job it won’t be hitting us!
|Size||~400 m in diameter|
|Mass||90 – 100 million metric tonnes|
|Closest distance to Earth on Nov. 8||325,000 km at 23:29 UTC (18:29 ET)|
|Closest distance to Moon on Nov. 9||239,867 km at 07:20 UTC (02:20 ET)|
|Speed at flyby||~49,400 km/h (~30,700 mph)|
|Spin period||~18 hours|
|Orbital period around Sun||1.22 years|
|Perihelion distance||0.65 AU (97,240 km)|
|Aphelion distance||1.63 AU (243,850 km)|
By comparison, the Earth has a mass of ~6,000 trillion tonnes, while the Moon’s is ~70 trillion tonnes; it’s clear 2005 YU55 would be on the losing end of a gravitational battle. The Moon is an average of 384,400 km from Earth, so 2005 YU55 will pass about 85% of that distance, though it will never be between Earth and the Moon.
Below are two animations I’ve created for you (using the ORSA package developed by Pasquale Tricarico); the first one shows the passage of 2005 YU55 from a point of view slightly above the plane of the Moon’s orbit (with the Sun to the left); the second animation shows what you would see if you were travelling on the asteroid itself looking towards the Moon. Notice how the asteroid flies high over the plane of the Moon’s orbit and never intersects either the path of the Earth around the Sun or that of the Moon around the Earth. Neither the Earth nor the Moon are ever in any danger of getting in the way! Click the animations to see them in 720 HD.
Observing 2005 YU55
Want to take a stab at observing this asteroid as it flies by Earth? It’s going to be no brighter than magnitude +10 (the dimmest object you can see with the naked eye is about +6), but if you have a telescope with an aperture greater than 15 cm, here is a nice guide by David Dickinson at the Astro Guyz blog:
If you want to watch this event from the comfort of your own home, you can do so on the Slooh Space Camera site.