On November 8 Asteroid 2005 YU 55 passed within 325,000 km from Earth. Using Swift’s UltraViolet/Optical Camera in a special observing mode called ‘event mode’, we were able to observe the asteroid as it quickly zipped by Earth.

Our observations showed that the 308 meter sized asteroid is very dark, reflecting only 6% of all visual light, and 5% of UV light from the Sun (making this asteroid is about twice as dark as coal!). The orbit of the asteroid also allowed us to measure how the object reflected light under different illumination angles. We concluded that both the color and albedo of 2005 YU 55 are characteristic of that of C-type asteroids, a class of asteroids that dominates the main belt but is relatively rare around Earth.

Published as an electronic telegram by the Central Bureau for Astronomical Telegrams on Dec 5, 2011; CBET #2937 available here

BELOW: Using a special observing technique Swift was able to capture the small asteroid YU55 when it zipped by Earth. The image shows the trajectory of the fast-moving asteroid on the chip.