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“Freakish” asteroid resembles spinning sprinkler

Nov. 8, 2013
Courtesy of the Uni­vers­ity of California-Los An­ge­les 
and World Science staff

As­tro­no­mers have found a “weird and freak­ish ob­ject” re­sem­bling a spin­ning lawn sprink­ler in the as­ter­oid belt be­tween Mars and Ju­pi­ter.

The find, re­ported on­line in the Nov. 7 is­sue of the jour­nal As­t­ro­phys­i­cal Jour­nal Let­ters, has left them scratch­ing their heads for an ex­plana­t­ion. Nor­mal as­ter­oids ap­pear simply as ti­ny points of light. This bi­zarre one has six com­et-like tails of dust ra­di­at­ing from it like spokes on a wheel.

Credit: NASA, ESA, and D. Jewitt (UCLA)


“It’s hard to be­lieve we’re look­ing at an as­ter­oid,” said lead in­ves­ti­ga­tor Da­vid Je­witt, of the Uni­vers­ity of California-Los An­ge­les. “We were dumb­founded when we saw it. Amaz­ing­ly, its tail struc­tures change dra­mat­ic­ally in just 13 days as it belches out dust.” 

One pos­si­bil­ity is that thanks to in­creas­ingly fast spin, the as­ter­oid’s sur­face started fly­ing apart, spit­ting out dust in bursts start­ing last spring, the re­search­ers added.

It was first seen as an un­usu­ally fuzzy ob­ject with the Pan-STARRS sur­vey tel­e­scope in Ha­waii. Its mul­ti­ple tails were dis­cov­ered in im­ages tak­en by NASA’s Hub­ble Space Tel­e­scope on Sept. 10. When Hub­ble re­turned to the as­ter­oid on Sept. 23, it looked as if the whole struc­ture had swung around.

“We were com­pletely knocked out,” said Je­witt.

The tails could have aris­en from a se­ries of “im­pul­sive dust-e­jec­tion events,” mod­el­ing by team mem­ber Jes­si­ca Agar­wal in­di­cat­ed. Agar­wal, of the Max Planck In­sti­tute for So­lar Sys­tem Re­search in Lin­dau, Ger­ma­ny, cal­cu­lat­ed that the first ejec­tion oc­curred on April 15 and the last on Sept. 4. The ones in be­tween were on July 18, July 24, Aug. 8 and Aug. 26.

Pres­sure from the sun’s radia­t­ion smears the dust in­to stream­ers. The as­ter­oid may have been “spun up” if that pres­sure ex­erted a torque, or twist­ing force, Je­witt said. If the spin got fast enough, he added, the ob­ject’s weak gra­vity would no long­er be able to hold it to­geth­er. Dust might av­a­lanche to­ward its equa­tor and even­tu­ally drift in­to space to make a tail. So far, less than a thou­sandth of the as­ter­oid’s con­tent has been lost—per­haps 100 to 1,000 tons of dust, Je­witt said.

Fol­low-up ob­serva­t­ions may show wheth­er the dust leaves the as­ter­oid in the equa­torial plane; that would in­di­cate a “rota­t­ional breakup,” Je­witt said. This must be a com­mon phe­nom­e­non in the as­ter­oid belt, Je­witt said, and may even be the main way that small as­ter­oids die. “In as­tron­o­my, where you find one, you even­tu­ally find a whole bunch more,” he said.

The ob­ject may be a piece from an as­ter­oid col­li­sion around 200 mil­lion years ago, Je­witt added. The re­sult­ing frag­ments, known as the Flo­ra as­ter­oid fam­i­ly, are still fol­low­ing si­m­i­lar or­bits around the sun. Me­te­orites from these bod­ies show ev­i­dence of hav­ing been heat­ed to as much as 1,500 de­grees Fahr­en­heit (800 Cel­sius).


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Astronomers have found a “weird and freakish object” resembling a spinning lawn sprinkler in the asteroid belt between Mars and Jupiter. The find, reported online in the Nov. 7 issue of the Astrophysical Journal Letters, has left them scratching their heads for an explanation. Normal asteroids appear simply as tiny points of light. This bizarre one has six comet-like tails of dust radiating from it like spokes on a wheel. “It’s hard to believe we’re looking at an asteroid,” said lead investigator David Jewitt, of the University of California-Los Angeles. “We were dumbfounded when we saw it. Amazingly, its tail structures change dramatically in just 13 days as it belches out dust.” One possibility is that thanks to increasingly fast spin, the asteroid’s surface started flying apart, spitting out dust in bursts starting last spring, the researchers added. It was first seen as an unusually fuzzy object with the Pan-STARRS survey telescope in Hawaii. Its multiple tails were discovered in images taken by NASA’s Hubble Space Telescope on Sept. 10. When Hubble returned to the asteroid on Sept. 23, it looked as if the whole structure had swung around. “We were completely knocked out,” said Jewitt. The tails could have arisen from a series of “impulsive dust-ejection events,” modeling by team member Jessica Agarwal indicated. Agarwal, of the Max Planck Institute for Solar System Research in Lindau, Germany, calculated that the first ejection occurred on April 15 and the last on Sept. 4. The ones in between were on July 18, July 24, Aug. 8 and Aug. 26. Pressure from the sun’s radiation smears the dust into streamers. The asteroid may have been “spun up” if that pressure exerted a torque, or spinning force, Jewitt said. If the spin got fast enough, he added, the object’s weak gravity would no longer be able to hold it together. Dust might avalanche toward the asteroid’s equator and eventually drift into space to make a tail. So far, less than a thousandth of the asteroid’s main mass has been lost—perhaps 100 to 1,000 tons of dust, Jewitt said. Follow-up observations may show whether the dust leaves the asteroid in the equatorial plane; that would indicate a “rotational breakup,” Jewitt said. This must be a common phenomenon in the asteroid belt, Jewitt said, and may even be the main way that small asteroids die. “In astronomy, where you find one, you eventually find a whole bunch more,” he said. The object may be a piece from an asteroid collision that occurred roughly 200 million years ago, Jewitt added. The resulting fragments, known as the Flora asteroid family, are still following similar orbits around the sun. Meteorites from these bodies show evidence of having been heated to as much as 1,500 degrees Fahrenheit (800 Celsius).