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Distant solar system forming from mysterious dust, scientists say

Jan. 11, 2010
Courtesy Gemini Observatory
and World Science staff

A far-off so­lar sys­tem seems to be form­ing from a strange dust whose make­up is un­like that of our and oth­er so­lar sys­tems, as­tro­no­mers say.

The researchers at the Univers­ity of Cal­i­for­nia Los An­ge­les found ev­i­dence for the forma­t­ion of young, rocky plan­ets from dust cir­cling a star some 500 light-years away. A light-year is the dis­tance light trav­els in a year. 

Artist'sren­der­ing of what HD 131488's in­ner plan­e­tary sys­tem might look like as two large rocky bod­ies col­lide. In­set il­lus­trates the lo­ca­tion of HD 131488's dust belts (top) and com­pa­ra­ble re­gions to our own So­lar Sys­tem (bot­tom). HD 131488's hot in­ner dust belt has si­m­i­lar sep­a­ra­tions from its host star as the ter­res­tri­al plan­et zone around our Sun while the star's cool dust belt has si­m­i­lar sep­a­ra­tions from its host star as the Kuiper Belt re­gion in our So­lar Sys­tem. Al­so shown for our So­lar Sys­tem are the or­bits of Ju­pi­ter, Sat­urn, Ura­nus, and Nep­tune.</font> (Cour­te­sy Gem­i­ni Ob­serv­a­to­ry)


“Un­til now, warm dust found around oth­er stars has been very si­m­i­lar in com­po­si­tion to as­ter­oi­dal or com­et­ary ma­te­ri­al in our So­lar Sys­tem,” said the uni­vers­ity’s Carl Melis, who led the re­search while a grad­u­ate stu­dent. 

But this case is diff­er­ent, he said.

“Typic­ally, dust de­bris around oth­er stars, or our own Sun, is of the ol­i­vine, py­rox­ene, or sil­ica va­ri­e­ty, min­er­als com­monly found on Earth,” he noted. But this ma­te­ri­al “is not one of these dust types. We have yet to iden­ti­fy what spe­cies it is.” 

Melis re­ported the find­ings last Wednes­day at the annual Amer­i­can As­tro­nom­i­cal So­ci­e­ty meet­ing in Wash­ing­ton, D.C.

The star, known as HD 131488, ap­pears to be sur­rounded by warm dust in a re­gion called the ter­res­tri­al plan­et zone, where tem­per­a­tures are si­m­i­lar to those on Earth, Melis said. He added that the dust seems to harbor rocky, emb­ry­onic planets that have re­cently coll­ided.

“What makes HD 131488 truly un­ique is the un­iden­ti­fied dust spe­cies re­leased from the col­lid­ing bod­ies as well as the pres­ence of cold dust far away from the star,” said as­tron­o­mer Ben­ja­min Zuck­er­man of the univers­ity, a co-author of the re­search. “These two char­ac­ter­is­tics make HD 131488 un­like any oth­er star with ev­i­dence for mas­sive quanti­ties of dust in its ter­res­tri­al plan­et zone.”

The re­search­ers an­a­lyzed the warm in­ner dust through in­fra­red im­ag­ing and spec­tros­co­py us­ing an in­stru­ment called T-ReCS on the Gem­i­ni South tel­e­scope in Chil­e. Spec­tros­co­py is the anal­y­sis of the com­po­si­tion of ob­jects us­ing the spec­trum of light they give off.

Melis and his team ar­gue that the most plau­si­ble ex­plana­t­ion for the un­usu­al abun­dance of warm dust is a re­cent col­li­sion of two rocky plan­e­tary mass bod­ies.

While the mys­te­ri­ous warm dust lies at a dis­tance from HD 131488 that is com­pa­ra­ble to the Earth-Sun separa­t­ion, the team al­so found cool­er dust about 45 times fur­ther out. This out­er dusty re­gion is anal­o­gous to the Kuiper Belt in our own So­lar Sys­tem where many mi­nor plan­ets or­bit the Sun just be­yond the or­bit of Nep­tune.

“The hot dust al­most cer­tainly came from a re­cent cat­a­stroph­ic col­li­sion be­tween two large rocky bod­ies in HD 131488’s in­ner plan­e­tary sys­tem,” Melis said. But the cool­er dust “is probably left over from plan­et forma­t­ion that took place far­ther away from HD 131488.” 

HD 131488 lies in the di­rec­tion of the con­stella­t­ion Cen­tau­rus and is three times heav­i­er and 33 times more lu­mi­nous than our own Sun. The star is part of a ma­jor, south­ern-hem­i­sphere star form­ing re­gion known as the Upper-Cen­tau­rus-Lupus as­socia­t­ion whose mem­bers are be­lieved to be about 10 mil­lion years old. By con­trast, the Sun and Earth are about 4.6 bil­lion years old.


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A far-off solar system seems to be forming out of a strange dust whose makeup is unlike that of our and other solar systems, astronomers say. Astronomers at the University of California at Los Angeles found evidence for the formation of young, rocky planets from dust circling a star some 500 light-years away. A light-year is the distance light travels in a year. But in the aftermath of collisions between planetary embryos in the dust, the debris bears no resemblance to the planetary building blocks of our own Solar System, the scientists say. “Until now, warm dust found around other stars has been very similar in composition to asteroidal or cometary material in our Solar System,” said the university’s Carl Melis, who led the research while a graduate student. “This newly discovered dusty star is a compelling exception.” “Typically, dust debris around other stars, or our own Sun, is of the olivine, pyroxene, or silica variety, minerals commonly found on Earth,” he added. “The material orbiting HD 131488 is not one of these dust types. We have yet to identify what species it is—it really appears to be a completely alien type of dust.” Melis reported the findings last Wednesday at the American Astronomical Society meeting in Washington, D.C. The star, known as HD 131488, appears to be surrounded by warm dust in a region called the terrestrial planet zone, where the star heats the dust to temperatures similar to those found on Earth, Melis said. “What makes HD 131488 truly unique is the unidentified dust species released from the colliding bodies as well as the presence of cold dust far away from the star,” said astronomer Benjamin Zuckerman of the university, a co-author of the research. “These two characteristics make HD 131488 unlike any other star with evidence for massive quantities of dust in its terrestrial planet zone.” The researchers analyzed the warm inner dust through infrared imaging and spectroscopy using an instrument called T-ReCS on the Gemini South telescope in Chile. Spectroscopy is the analysis of the composition of objects using the spectrum of light they give off. Melis and his team argue that the most plausible explanation for the unusually large quantity of warm dust is a recent collision of two rocky planetary mass bodies. Such a collision would provide an appropriate source of dust particles needed to explain the observations. While the mysteriously composed warm dust is located at a distance from HD 131488 that is comparable to the Earth-Sun separation, the team also found cooler dust about 45 times further out. This outer dusty region is analogous to the Kuiper Belt in our own Solar System where many minor planets orbit the Sun just beyond the orbit of Neptune. “The hot dust almost certainly came from a recent catastrophic collision between two large rocky bodies in HD 131488’s inner planetary system,” Melis said. But the cooler dust “is probably left over from planet formation that took place farther away from HD 131488.” HD 131488 lies in the direction of the constellation Centaurus and is three times heavier and 33 times more luminous than our own Sun. The star is part of a major southern hemisphere star forming region known as the Upper-Centaurus-Lupus association whose members are believed to be about 10 million years old. By contrast, the Sun and Earth are about 4.6 billion years old.