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

RETURN TO THE WORLD SCIENCE HOME PAGE


Asteroid is leading Earth in strange dance, astronomers say

July 28, 2011
Courtesy of NASA
and World Science staff

A new­found as­ter­oid is locked in a strange dance with our plan­et—trav­el­ing ahead of Earth in its path around the Sun, but adding some moves of its own along the way, as­tro­no­mers say.

Re­search­ers say the find­ing now puts Earth in com­pa­ny with at least five oth­er plan­ets or moons in the So­lar Sys­tem that al­so have so-called “Tro­jan” com­pan­ion bodies. These are ob­jects that fol­low be­hind, or lead in front of, a plan­et or moon in its or­bit.

An animation il­lus­trates the or­bit of 2010 TK7 (green dots). (Cour­tesy NA­SA)


“Tro­jans” in­hab­it ar­eas where the gravita­t­ional forc­es be­tween the cen­tral body and the larg­er or­bit­ing body bal­ance out, so that the Tro­jans can stay in that same place re­la­tive to them for many years. Each or­biting body is as­so­ci­at­ed with two such “tri­an­gu­lar points”: one be­hind, one in front it along the or­bit. Each point is sep­a­rat­ed by the main or­biting body by one-sixth of the dis­tance cov­ered by the whole or­bit.

In this case, “it’s as though Earth is play­ing fol­low the lead­er,” said re­search­er Amy Mainzer of NASA’s Je­t Pro­pul­sion Lab­o­r­a­to­ry in Pas­a­de­na, Calif., prin­ci­pal in­ves­ti­ga­tor of the proj­ect that led to the find­ing. “Earth al­ways is chas­ing this as­ter­oid around.” They are not ex­pected to col­lide, she added.

The “Tro­jan,” dubbed 2010 TK7, is­n’t just blandly plow­ing through space along the same, roughly cir­cu­lar path that Earth fol­lows, as­tro­no­mers say. In­stead­—if we en­vi­sion Earth as a point mov­ing along the edge of a plate, with the Sun in the mid­dle—the Tro­jan would be snak­ing around and around a point in front of Earth. Our plan­et’s own gra­vity con­tri­butes to the weird play of forc­es that make this hap­pen.

The tiny dancer ahead of us is rath­er dif­fer­ent from anoth­er as­ter­oid re­portedly discov­ered as a com­pan­ion to Earth ear­li­er this year. That ob­ject is not be­lieved to be a Tro­jan, though sci­en­tists say it may have been one once. It’s in­stead de­scribed as a “horse­shoe” com­pan­ion, be­cause of the shape of the path it traces out in the sky with re­spect to our point of view. That ob­ject is al­so ex­pected to probably leave Earth’s neigh­bor­hood with­in the next mil­lion years or so. The au­thors of the new study did­n’t ven­ture pre­dic­tions that far ahead for their “Tro­jan,” but did say it will keep do­ing what it’s do­ing for at least 10,000 years.

Tro­jans are so called be­cause the first known ones, as­so­ci­at­ed with the plan­et Ju­pi­ter, were named af­ter fig­ures from the Tro­jan war saga.

Sci­en­tists had pre­dicted Earth should have Tro­jans, but they were hard to find be­cause they’re small and “d­well mostly in the day­light, mak­ing them very hard to see” for us, said Mar­tin Con­nors of Ath­a­bas­ca Uni­vers­ity in Can­a­da. “But we fi­nally found one, be­cause the ob­ject has an un­usu­al or­bit that takes it far­ther away from the sun than what is typ­i­cal for Tro­jans,” added Con­nors, lead au­thor of a pa­per on the find­ing in the July 28 is­sue of the re­search jour­nal Na­ture.

The discovery fi­nally came thanks to NASA’s Wide-field In­fra­red Sur­vey Ex­plor­er, or WISE, sa­tel­lite, as­tro­no­mers said. It “was a game-changer, giv­ing us a point of view dif­fi­cult to have at Earth’s sur­face,” Con­nors ex­plained. WISE’s tel­e­scope scanned the whole sky in in­fra­red light from Jan­u­ary 2010 to Feb­ru­ary 2011. Con­nors and his team be­gan their search for an Earth Tro­jan us­ing da­ta from NE­O­WISE, an ad­di­tion to the WISE mis­sion that fo­cused in part on near-Earth ob­jects, such as as­ter­oids and comets. 

The new­found ob­ject is roughly 1,000 feet (300 me­ters) wide, the re­search­ers said, and lies about 50 mil­lion miles (80 mil­lion kilome­ters) from Earth. They added that it would be im­prac­tical to send a probe there be­cause it would take too much fuel to reach it—given its fun­ny path—but that oth­er Earth-com­pan­ion as­ter­oids could make great tar­gets for ex­plora­t­ion.


* * *

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

A newfound asteroid is locked in a strange dance with our planet—traveling ahead of Earth in its path around the Sun, but adding some moves of its own along the way, astronomers say. Researchers say the finding puts Earth in company with at least five other planets or moons in the Solar System that also have so-called “Trojan” companions: bodies that follow behind, or lead in front of, a larger planet or moon in its orbit. “Trojans” inhabit areas where the gravitational forces between the central body and the larger orbiting body balance out, so that the Trojans can stay in that same place along the path for many years. Each orbiting body is associated with two such “triangular points”: one behind, one in front it along the orbit. Each point is separated by the main orbiting body by one-sixth of the distance covered by the whole orbit. In this case, “it’s as though Earth is playing follow the leader,” said researcher Amy Mainzer of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., principal investigator of the project that led to the finding. “Earth always is chasing this asteroid around.” They are not expected to collide, she added. The “Trojan,” dubbed 2010 TK7, isn’t just blandly plowing through space along the same, roughly circular path that Earth follows, astronomers say. Instead—if we envision Earth as a point moving along the edge of a plate, with the Sun in the middle—the Trojan would be snaking around and around a point in front of Earth. Our planet’s own own gravity contributes to the weird play of forces that make this happen. The object is rather different from another asteroid reportedly discovered to be a companion to Earth earlier this year. That object is not believed to be a Trojan, though scientists say it may have been one once. It’s instead described as a “horseshoe” companion to Earth, because of the path it traces out in the sky with respect to our point of view. That object is also expected to probably leave Earth’s neighborhood within the next million years or so. The authors of the new study didn’t venture predictions that far ahead for their “Trojan,” but did say it will keep doing what it’s doing for at least 10,000 years. Trojans are so called because the first known Trojans, associated with the planet Jupiter, were named after figures from the Trojan war. Scientists had predicted Earth should have Trojans, but they were hard to find because they’re small and “dwell mostly in the daylight, making them very hard to see” for us, said Martin Connors of Athabasca University in Canada, lead author of a paper on the discovery in the July 28 issue of the journal Nature. “But we finally found one, because the object has an unusual orbit that takes it farther away from the sun than what is typical for Trojans.” The discovery finally came thanks to NASA’s Wide-field Infrared Survey Explorer, or WISE, mission, astronomers said. It “was a game-changer, giving us a point of view difficult to have at Earth’s surface,” Connors explained. The WISE telescope scanned the whole sky in infrared light from January 2010 to February 2011. Connors and his team began their search for an Earth Trojan using data from NEOWISE, an addition to the WISE mission that focused in part on near-Earth objects, such as asteroids and comets. The newfound object is roughly 1,000 feet (300 meters) wide, the researchers said, and lies about 50 million miles (80 million kilometers) from Earth. They added that it would be hard to send a probe there because it would take too much fuel to reach it—given its funny path—though other companion asteroids to Earth could make great candidates for future exploration.