"Long before it's in the papers"
March 28, 2012

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Planets from long ago puzzle astronomers

March 28, 2012
Courtesy of the Max Planck Institute for Astronomy
and World Science staff

As­tro­no­mers have iden­ti­fied a plan­e­tary sys­tem that they de­scribe as a likely sur­vi­vor from one of the ear­li­est cos­mic times, 13 bil­lion years ago. 

The sys­tem, they say, con­sists of a star dubbed HIP 11952, and two plan­ets that or­bit it eve­ry 290 and sev­en Earth days, re­spec­tive­ly.

Artist’s im­pres­sion of HIP 11952 and its two Jupiter-like plan­ets. (Im­age cred­it: Tim­o­th­eos Sa­mar­t­zi­dis)
Most known plan­ets form in vast clouds that in­clude heav­i­er chem­i­cal el­e­ments, but this sys­tem is thought to con­tain very lit­tle be­sides the light­est ones, hy­dro­gen and he­li­um—a sign the sys­tem formed ear­ly.

As­tro­no­mers be­lieve the uni­verse orig­i­nally con­tained hy­dro­gen and he­li­um al­most ex­clu­sive­ly. Heav­i­er el­e­ments, which as­tro­no­mers re­fer to ge­ner­ic­ally as “met­als,” were pro­duced over time in stars, then flung in­to space as mas­sive stars died in gi­ant ex­plo­sions called su­per­novae. Plan­ets might not be able to form in ar­eas that are too poor in these heav­i­er el­e­ments, sci­en­tists say.

But the newly iden­ti­fied plan­ets came to light thanks to a sur­vey spec­i­fic­ally tar­get­ing metal-poor stars, car­ried out by a team of as­tro­no­mers in­clud­ing re­search­ers from the Max Planck In­sti­tute for As­tron­o­my in Hei­del­berg, Ger­ma­ny. The star, ex­tremely metal-poor and old, lies in the di­rec­tion of the con­stella­t­ion Ce­tus (“the whale” or “the sea mon­ster”) at a dis­tance of about 375 light-years from Earth.

“In 2010 we found the first ex­am­ple of such a metal-poor sys­tem, HIP 13044. Back then, we thought it might be a un­ique case; now, it seems as if there might be more plan­ets around metal-poor stars than ex­pect­ed,” said Ve­ron­i­ca Roc­catagli­ata of Uni­vers­ity Ob­serv­a­to­ry Mu­nich, the prin­ci­pal in­ves­ti­ga­tor of the sur­vey.

HIP 11952 is es­ti­mat­ed to be 12.8 bil­lion years old. “This is an ar­chae­o­log­i­cal find in our own back­yard,” said Johny Se­ti­awan of the Max Planck In­sti­tute, who led the study of the star. “These plan­ets probably formed when our Gal­axy it­self was still a ba­by.”

“We would like to disco­ver and study more plan­e­tary sys­tems of this kind. That would al­low us to re­fine our the­o­ries of plan­et forma­t­ion. The disco­very of the plan­ets of HIP 11952 shows that plan­ets have been form­ing through­out the life of our Uni­verse,” added An­na Pasquali of Hei­del­berg Uni­vers­ity, a co-author of the pa­per.

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Astronomers have identified a planetary system that they describe as a likely survivor from one of the earliest cosmic times, 13 billion years ago. The system, they say, consists of a star dubbed HIP 11952, and two planets that orbit it every 290 and seven Earth days, respectively. Most known planets form in vast clouds that include heavier chemical elements, but this system is thought to contain very little besides the lightest, hydrogen and helium—an indicator that the system formed early. Astronomers believe the universe originally contained hydrogen and helium almost exclusively. Heavier elements, which astronomers refer to generically as “metals,” were produced over time in stars, then flung into space as massive stars died in giant explosions called supernovae. Planets might not be able to form in areas that are too poor in these heavier elements, scientists say. But the newly identified planets came to light thanks to a survey targeting metal-poor stars, carried out by a team of astronomers including researchers from the Max Planck Institute for Astronomy in Heidelberg, Germany. The star, extremely metal-poor and old, lies in the direction of the constellation Cetus (“the whale” or “the sea monster”) at a distance of about 375 light-years from Earth. “In 2010 we found the first example of such a metal-poor system, HIP 13044. Back then, we thought it might be a unique case; now, it seems as if there might be more planets around metal-poor stars than expected,” said Veronica Roccatagliata of University Observatory Munich, the principal investigator of the survey. HIP 11952 is estimated to be 12.8 billion years old. “This is an archaeological find in our own backyard,” said Johny Setiawan of the Max Planck Institute, who led the study of the star. “These planets probably formed when our Galaxy itself was still a baby.” “We would like to discover and study more planetary systems of this kind. That would allow us to refine our theories of planet formation. The discovery of the planets of HIP 11952 shows that planets have been forming throughout the life of our Universe”, added Anna Pasquali of Heidelberg University, a co-author of the paper.