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May 01, 2011
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Asteroid grows “tail” after apparent crash with smaller kin
May 1, 2011
Courtesy of NASA
and World
Science staff
Scientists say they
have for the first time photographed the recent aftermath of a collision between asteroids,
which caused the larger one to grow a comet-like “tail” for a few
weeks. Scheila is overexposed in this image to reveal the faint dust features. The asteroid is surrounded by a C-shaped cloud of particles and displays a linear dust tail in this visible-light picture acquired by Hubble's Wide Field Camera 3. Because Hubble tracked the asteroid during the exposure, the star images are trailed.
(Credits: NASA Artist's conception
of
the impact presumed to have created plumes trailing off of Asteroid
Scheila. (Courtesy NASA)
Astronomers claim the encounter occurred last last year when a 100-foot (30 meter) boulder careened into the much larger, Sun-orbiting asteroid Scheila. Flying in at more than three times the speed of the fastest bullets, the projectile is thought to have struck with the force of a 100-kiloton nuclear bomb. This caused Scheila to give off more than 660,000 tons of dust, almost twice the weight in material of the Empire State Building—which
became the “tail.”
“This is the first time we’ve been able to catch [a collision between asteroids] just weeks after the smash-up, long before the evidence fades away,” said Dennis Bodewits of the University of Maryland in College Park, lead author of a study on the findings to appear in the May 20 issue of the journal
Astrophysical Journal Letters.
Asteroids are believed to collide fairly often—many are heavily
cratered—but catching such an event is not easy.
Late last year, astronomers noticed that Scheila had unexpectedly brightened and was sporting short-lived plumes. Data from NASA’s Swift satellite and Hubble Space Telescope indicated the changes likely occurred after an impact, scientists said.
Asteroids are rocky fragments thought to be debris from the formation and evolution of the
Solar System about 4.6 billion years ago. Millions of them orbit the
Sun between Mars and Jupiter in an area called the asteroid belt. Scheila is about 70 miles wide and orbits the sun every five years.
“The Hubble data are most simply explained by the impact, at 11,000 mph, of a previously unknown asteroid about 100 feet in diameter,” said Hubble team leader David Jewitt at the University of California in Los Angeles. Hubble did not see any discrete collision fragments, apart from the dust plume, he added.
Astronomers have known for decades that comets contain icy material that erupts when warmed by the sun. They regarded asteroids as inactive rocks whose destinies, surfaces, shapes and sizes were determined by mutual impacts. However, this simple picture has grown more complex over the past few years.
During certain parts of their orbits, some objects, once categorized as asteroids, develop comet-like features that can last for many months. Others display much shorter outbursts. Icy materials may be occasionally exposed, either by internal geological processes or by an external one, such as an impact.
On Dec. 11, images from the University of Arizona’s Catalina Sky Survey, a NASA project, revealed 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.
Swift’s Ultraviolet/Optical Telescope soon thereafter captured multiple images and measured the spectrum of light from the asteroid. This data ruled out that it could be a comet, scientists said. Two dust plumes flanked the object, a bright one in the north and a fainter one in the south. The plumes, astronomers said, formed as sunlight gently pushed on dust particles blown off by the impact. Hubble also observed the fading dust cloud on Dec. 27 and Jan. 4.
The dust probably formed separate plumes because the projectile struck a low angle, researchers said.
“The dust cloud around Scheila could be 10,000 times as massive as the one ejected from comet 9P/Tempel 1” during NASA’s Deep Impact mission, said study co-author Michael Kelley, also at the University of Maryland. “Collisions allow us to peek inside comets and asteroids,” he continued. Material “kicked up by Deep Impact contained lots of ice, and the absence of ice in Scheila’s interior shows that it’s entirely unlike comets.”
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Scientists have identified the recent aftermath of a collision between asteroids for the first time, and say the larger body grew a comet-like “tail” of dust after the crash. Astronomers claim the encounter occurred last last year when a 100-foot (30 meter) boulder careened into the much larger, Sun-orbiting asteroid Scheila. Flying in at more than three times the speed of the fastest bullets, the projectile is thought to have struck with the force of a 100-kiloton nuclear bomb. This caused Scheila to give off more than 660,000 tons of dust, almost twice the weight in material of the Empire State Building—explaining the “tail.” “This is the first time we’ve been able to catch [a collision between asteroids] just weeks after the smash-up, long before the evidence fades away,” said Dennis Bodewits of the University of Maryland in College Park, lead author of a study on the findings to appear in the May 20 issue of the journal Astrophysical Journal Letters. Late last year, astronomers noticed that Scheila had unexpectedly brightened and was sporting short-lived plumes. Data from NASA’s Swift satellite and Hubble Space Telescope indicated the changes likely occurred after an impact, scientists said. Asteroids are rocky fragments thought to be debris from the formation and evolution of the solar system about 4.6 billion years ago. Millions of them orbit the sun between Mars and Jupiter in an area called the asteroid belt. Scheila is about 70 miles wide and orbits the sun every five years. “The Hubble data are most simply explained by the impact, at 11,000 mph, of a previously unknown asteroid about 100 feet in diameter,” said Hubble team leader David Jewitt at the University of California in Los Angeles. Hubble did not see any discrete collision fragments, apart from the dust plume, he added. Astronomers have known for decades that comets contain icy material that erupts when warmed by the sun. They regarded asteroids as inactive rocks whose destinies, surfaces, shapes and sizes were determined by mutual impacts. However, this simple picture has grown more complex over the past few years. During certain parts of their orbits, some objects, once categorized as asteroids, develop comet-like features that can last for many months. Others display much shorter outbursts. Icy materials may be occasionally exposed, either by internal geological processes or by an external one, such as an impact. On Dec. 11, images from the University of Arizona’s Catalina Sky Survey, a NASA project, revealed 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. Swift’s Ultraviolet/Optical Telescope soon thereafter captured multiple images and measured the spectrum of light from the asteroid. This data ruled out that it could be a comet, scientists said. Two dust plumes flanked the object, a bright one in the north and a fainter one in the south. The plumes, astronomers said, formed as sunlight gently pushed on dust particles blown off by the impact. Hubble also observed the fading dust cloud on Dec. 27 and Jan. 4. The dust probably formed two separate plumes because the projectile struck a low angle, researchers said. “The dust cloud around Scheila could be 10,000 times as massive as the one ejected from comet 9P/Tempel 1” during NASA’s Deep Impact mission, said study co-author Michael Kelley, also at the University of Maryland. “Collisions allow us to peek inside comets and asteroids,” he continued. Material “kicked up by Deep Impact contained lots of ice, and the absence of ice in Scheila’s interior shows that it’s entirely unlike comets.”