Asteroid 2005 YU55 was listed on NASA's "Sentry Risk Page" as having as small (about one in 10 million) chance of hitting the Earth in the next century. We observed this asteroid with the Arecibo Planetary Radar system on April 19-23 2010.
Previous to April 2010, several hundred optical observations over 5 years had identified potential Earth impacts. A few Arecibo radar measurements over two days showed that no impacts would occur. A very close pass by Earth would take place November 8, 2011.
These observations in 2010 measured the distance to the asteroid at a resolution of 7.5 meters, (about 25 feet), when it was over a million miles away. The observations on November 8 2011 will also measure the distance to within 25 feet, but the asteroid will only be 205,000 miles away, about an hour and a half before its closest approach to the Earth.
The object poses no hazard to the Earth through at least 2075.
Image courtesy Michael C. Nolan and Ellen S. Howell, Arecibo Observatory.
Range increases downward, frequency increases to the right. range scale is 0.05 us (7.5 m) per pixel. Frequency resolution is 0.025 Hz.
We obtained radar images of asteroid 2005 YU55 at 11 PM local time on 2011 Nov 9 using the Arecibo Observatory Planetary Radar System in Puerto Rico and the Robert W. Byrd Green Bank Telescope in West Virginia.
The Arecibo systems transmitted a half-million-Watt radio signal towards the asteroid, a tiny fraction of which was reflected back towards the Earth and detected at Green Bank. This image has a resolution of 15 meters, about 50 feet per pixel. The asteroid is about 400m, 1300 feet, in diameter, and was about 1.4 million km, or 800000 miles away at the time of observations.
Image courtesy Patrick Taylor, Arecibo Observatory and Frank Ghigo, National Radio Astronomy Observatory.
We will use these images, along with images taken last week using the Goldstone radar system in California, to determine the size and shape of the asteroid, study its surface properties, and help predict its future encounters with the Earth. Many observers at telescopes all around the world have been studying this object, and by combining data from all of these sources, we will get as complete a picture of the object as is possible from the Earth, comparable to that obtained in a "flyby" spacecraft mission.
Additional images were obtained nightly through November 14.
Range increases downward, frequency increases to the right. range scale is 0.05 us (7.5 m) per pixel.
7.5-m Arecibo monostatic imaging of 2005 YU55 by Patrick Taylor.
7.5-m Arecibo monostatic imaging of 2005 YU55 by Patrick Taylor. Radar bright feature, possibly a boulder on the asteroid's surface.
The Arecibo Observatory is operated by SRI International under a cooperative agreement with the National Science Foundation (AST-1100968), and in alliance with Ana G. Méndez-Universidad Metropolitana, and the Universities Space Research Association, with additional funding from NASA.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Last modified 2011 November 14
Ellen Howell Michael C. Nolan