Newly released data from NASA’s Swift satellite and Hubble Space Telescope suggest a small asteroid named Scheila that unexpectedly brightened late last year likely had just been struck by a much smaller asteroid, according to a NASA press release.
“Collisions between asteroids create rocket fragments, from fine dust to huge boulders, that impact planets and their moons,” Dennis Bodewits, a University of Maryland astronomer and lead author of the Swift study, said in the April 28 press release. “Yet this is the first time we’ve been able to catch one just weeks after the smash-up, long before the evidence fades away.”
Scheila, which orbits the sun every five years, measures approximately 112 kilometers across.
On Dec. 11, images from the University of Arizona’s Catalina Sky Survey, a project of NASA’s Near Earth Object Observations Program, showed Scheila to be twice as bright as expected and immersed in a faint comet-like glow, NASA said. By looking at archived images, astronomers inferred that 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. The absence of gas around Scheila led the Swift team to reject scenarios where exposed ice accounted for the activity.
Other images, meanwhile, showed the asteroid flanked in the north by a bright dust plume and in the south by a fainter one. Hubble observed Schella’s fading dust cloud Dec. 27 and Jan. 4.
The two teams concluded the observations were best explained by a collision with a small asteroid that likely left a crater 300 meters across and ejected more than 580 metric tons of dust.
“The dust cloud around Scheila could be 10,000 times as massive as the one ejected from comet 9P/Tempel 1 during NASA’s [University of Maryland-led] Deep Impact mission,” study co-author Michael Kelley, also of the University of Maryland, said in the release. “Collisions allow us to peek inside comets and asteroids. Ejecta kicked up by Deep Impact contained lots of ice, and the absence of ice in Scheila’s interior show that it’s entirely unlike comets.”