"Long before it's in the papers"
January 27, 2015

RETURN TO THE WORLD SCIENCE HOME PAGE


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.

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.”

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/E­SA/D. Je­witt (UCLA))


“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.

Artist's con­ce­ption of the im­pact pre­sumed to have cre­at­ed plumes trail­ing off of As­ter­oid Scheila. (Cour­te­sy NA­SA)


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.”


* * *

Send us a comment on this story, or send it to a friend









 

Sign up for
e-newsletter
   
 
subscribe
 
cancel

On Home Page         

LATEST

  • St­ar found to have lit­tle plan­ets over twice as old as our own

  • “Kind­ness curricu­lum” may bo­ost suc­cess in pre­schoolers

EXCLUSIVES

  • Smart­er mice with a “hum­anized” gene?

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find

  • Could simple an­ger have taught people to coop­erate?

MORE NEWS

  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

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.”