Asteroid video captured by NASA's Swift satellite

November 11, 2011

UNIVERSITY PARK, Pa. -- As an asteroid the size of an aircraft carrier streaked past Earth during the early-morning hours last week, a team of astronomers at Penn State University and other institutions using NASA's Swift satellite monitored the fast-moving space rock, as did other professional and amateur astronomers using other instruments around the globe. The Swift satellite was the only observatory that captured the asteroid's ultraviolet emissions. Scientists now can use these ultraviolet data to understand the asteroid's surface composition and to more precisely predict the path of its future fly-bys near Earth.

"Catching a fast-moving target like this asteroid from an orbiting observatory like Swift requires extra care and attention," said Jamie Kennea, leader of the Science Operations Team for the Swift mission at Penn State. "An asteroid like this one is easy to miss, but Swift's unique rapid-response agility, plus the hard work of the team at the Penn State Mission Operations Center, allowed us to capture images of the asteroid not just once, but twice as it zipped by."

The 27-minute-long image was effectively sliced into short 10-second-long exposures, which then were combined into a movie that allows scientists to study short-term brightness variations caused by the object's rotation (watch the movie here: result is a movie of 2005 YU55 at ultraviolet wavelengths unobtainable from ground-based telescopes. For planetary scientists, this movie is a treasure trove of data that will help them to better understand how this asteroid is put together -- information that may help to make predictions of its motion more secure for centuries to come.

The asteroid, named "2005 YU55," whisked through the field of view of Swift's Ultraviolet/Optical Telescope (UVOT) on Nov. 9, just hours after the space rock made its closest approach to Earth. Swift's video of the fly-by plays on a background image from the Digital Sky Survey that shows the same region, which lies within the star pattern known as the Great Square in the constellation Pegasus. The flight times of the asteroid are noted in Universal Time during the video.

"Swift's ultraviolet and X-ray capabilities give scientists a unique perspective on comets and asteroids, expanding the spectral window beyond the radio, infrared and optical observations so well handled by big ground-based facilities," said Sergio Campana, a Swift team member at Brera Observatory in Merate, Italy. Campana made the request to interrupt the Swift satellite's observing schedule in order to use its powerful telescopes during the fleeting opportunity for observing the asteroid.

Although Swift is better known for its study of higher-energy X-ray and gamma-ray outbursts from cosmic explosions, the versatile satellite also has made valuable observations of passing comets and asteroids. All told, the spacecraft has observed ten asteroids, including Vesta -- now being studied close-up by NASA's Dawn spacecraft -- and Scheila, which brightened unexpectedly in late 2010 after colliding with a much smaller asteroid.

Classified as a potentially hazardous object, 2005 YU55 poses no threat of colliding with Earth for at least the next century. But understanding the details of how its surface reflects light and heat will allow improved assessments of future hazards. A body in space absorbs sunlight and reradiates the energy as heat, and both of these processes produce a miniscule force that, over time, can alter the object's motion. "We observed the asteroid with Swift's Ultraviolet/Optical and X-ray telescopes but, as expected, we saw it only in the UV," said Dennis Bodewits, a Swift team member at the University of Maryland in College Park.

The challenge with 2005 YU55 was its rapid motion across the sky, which was much too fast for Swift to track. Instead, the team trained the spacecraft's optics at two locations along the asteroid's predicted path and let it streak through the field. The first exposure began a few hours after the asteroid's closest approach and fastest sky motion -- before 9 p.m. EST on 8 November -- but Swift detected only a weak signal then. Six hours later, around 3 a.m. EST on 9 November, Swift began an exposure that captured the asteroid sweeping through the Great Square of the constellation Pegasus. The 11th-magnitude rock then was 333,000 miles away from Earth and moving at 24,300 mph, about an hour after its closest approach to the moon.

That exposure gave the Swift team more than a streak through the stars. "A novel feature of Swift is the ability to go into the mode of tracking the arrival of every photon captured by the instrument. With that information, we can reconstruct the asteroid as a point source moving through the Ultraviolet/Optical Telescope's field of view," said Neil Gehrels, lead scientist for Swift at NASA's Goddard Space Flight Center in Greenbelt, Md.

The science and science and flight operations of the Swift observatory are controlled by Penn State from the Mission Operations Center in State College, Pa. Swift's X-Ray Telescope and UV/Optical Telescope were developed and built by international teams led by Penn State and drew heavily on each institution's experience with previous space missions.

For more information, contact Jamie Kennea at Penn State, at or 814-865-0234; Neil Gehrels at NASA Goddard, at or 301-286-6546; John Nousek at Penn State (director of the Mission Operations Center), at or 814-863-1937;
Lynn Cominsky (Swift PIO) at 707-664-2655 or; or Barbara Kennedy, Penn State Eberly College of Science PIO, at or 814-863-4682.


The science and science and flight operations of the Swift observatory are controlled by Penn State from the Mission Operations Center in State College, Pa. Swift's X-Ray Telescope and UV/Optical Telescope were developed and built by international teams led by Penn State and drew heavily on each institution's experience with previous space missions. The X-ray Telescope resulted from Penn State's collaboration with the University of Leicester in the United Kingdom and the Brera Astronomical Observatory in Italy. The Ultraviolet/Optical Telescope resulted from Penn State's collaboration with the Mullard Space Science Laboratory of the University College-London. Swift's gamma-ray detector, the Burst Alert Telescope, provides the rapid initial location and was built primarily by the NASA Goddard Space Flight Center in Greenbelt, Md., and Los Alamos National Laboratory in New Mexico and was constructed at GSFC. These three telescopes give Swift the ability to do almost immediate follow-up observations of most gamma-ray bursts because Swift can rotate so quickly to point toward the source of the gamma-ray signal. The spacecraft was built by Spectrum Astro, which became part of General Dynamics and then part of Orbital Sciences Corporation. The Swift observatory was launched in November 2004 and was fully operational by January 2005. Swift carries three main instruments: the Burst Alert Telescope, the X-ray Telescope, and the Ultraviolet/Optical Telescope.

Last Updated January 17, 2012