Planets and Moons 

Swift and Hubble Probe an Asteroid Crash

Late last year, astronomers noticed that an asteroid named Scheila had unexpectedly brightened and it was sporting short-lived plumes. Data from NASA's Swift satellite and Hubble Space Telescope show that these changes likely occurred after Scheila was struck by a much smaller asteroid.

On Dec. 11, 2010, images from the University of Arizona's Catalina Sky Survey, a project of NASA's Near Earth Object Observations Program, revealed the Scheila to be twice as bright as expected and immersed in a faint comet-like glow. Looking through the survey's archived images, astronomers inferred the outburst began between Nov. 11 and Dec. 3.

Three days after the outburst was announced, Swift's Ultraviolet/Optical Telescope (UVOT) captured multiple images and a spectrum of the asteroid. Ultraviolet sunlight breaks up the gas molecules surrounding comets; water, for example, is transformed into hydroxyl (OH) and hydrogen (H). But none of the emissions most commonly identified in comets — such as hydroxyl or cyanogen (CN) — show up in the UVOT spectrum. The absence of gas around Scheila led the Swift team to reject scenarios where exposed ice accounted for the activity.

Images show the asteroid was flanked in the north by a bright dust plume and in the south by a fainter one. The dual plumes formed as small dust particles excavated by the impact were pushed away from the asteroid by sunlight. Hubble observed the asteroid's fading dust cloud on Dec. 27, 2010, and Jan. 4, 2011.

The two teams found the observations were best explained by a collision with a small asteroid impacting Scheila's surface at an angle of less than 30 degrees, leaving a crater 1,000 feet across. Laboratory experiments show a more direct strike probably wouldn't have produced two distinct dust plumes. The researchers estimated the crash ejected more than 660,000 tons of dust—equivalent to nearly twice the mass of the Empire State Building.

For the collision animation go here.

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Michael Lentz (UMBC): Lead Animator
Walt Feimer (HTSI): Animator
Scott Wiessinger (UMBC): Animator
Chris Smith (HTSI): Animator
Jake Dean (Aloe Design Studios): Animator
Chris Meaney (HTSI): Animator
Scott Wiessinger (UMBC): Video Editor
Scott Wiessinger (UMBC): Narrator
Scott Wiessinger (UMBC): Producer
Dennis Bodewits (University of Maryland College Park): Scientist
Francis Reddy (SPSYS): Writer
Scott Wiessinger (UMBC): Writer
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G2011-041 -- Swift Asteroid Collision

SVS >> Asteroid
SVS >> Dust
SVS >> Ultraviolet
SVS >> Hubble Space Telescope
SVS >> Astrophysics
SVS >> Solar System
SVS >> Edited Feature
SVS >> Space
SVS >> Swift
DLESE >> Narrated
SVS >> Collision
NASA Science >> Planets and Moons