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In a first, “cousin” planets reported

March 30, 2005
Courtesy 
and World Science staff

As­tro­no­mers say they have found two new plan­ets, each or­bit­ing one star—while the stars or­bit each oth­er. The re­search­ers are call­ing the Jupiter-sized plan­ets, tied in a strange, not-quite-sister rela­t­ion­ship, “cousin plan­ets.”

Most known plan­ets out­side our so­lar sys­tem or­bit stars that drift alone, like our Sun. 

Yet many stars are paired up in “bi­na­ry” sys­tems, twin stars formed from the same gas cloud, and which cir­cle each oth­er. Oc­ca­sion­ally as­tro­no­mers iden­ti­fy a plan­et that or­bits an en­tire bi­na­ry-star sys­tem, but re­search­ers say this is the first case where each bi­na­ry star seems to have its own sep­a­rately or­bit­ing world.

The find­ings, around stars known as WASP-94A and WASP-94B, were made by a team of Brit­ish, Swiss and Bel­gian as­tro­no­mers. The Brit­ish WASP-South sur­vey, op­er­ated by Keele Uni­vers­ity in the U.K., found ti­ny dips in the light of the first star, sug­gest­ing that a Jupiter-like plan­et was pass­ing in front of it. Swiss as­tro­no­mers then found ev­i­dence for plan­ets around both stars. 

“We ob­served the oth­er star by ac­ci­dent, and then found a plan­et around that one al­so!” said Mar­i­on Neveu-VanMalle of Ge­ne­va Ob­serv­a­to­ry, who wrote a pa­per on the find­ings. The report is online here.

The plan­ets are of a type known as “Hot Jupiters,” which or­bit so close to their suns that their “years” last only a few days. They are rare, the as­tro­no­mers said, so it would be un­likely to find two such plan­ets in the same star sys­tem by chance. Per­haps, they spec­u­late, WASP-94 has just the right con­di­tions for pro­duc­ing Hot Jupiters. If so, it could be an im­por­tant sys­tem for stu­dy­ing their de­vel­op­ment.

The ex­ist­ence of huge, Jupiter-size plan­ets so near to their stars is a long-stand­ing puz­zle, since it is be­lieved they can’t form near to the star, where it is far too hot. They must form much fur­ther out, where it is cool, then move clos­er, per­haps as a re­sult of an in­ter­ac­tion with anoth­er plan­et or star. The idea is that find­ing Hot Jupiters in two stars of a bi­na­ry pair might al­low us to study the pro­cesses that move the plan­ets in­ward.

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Astronomers have found two new planets, each orbiting one star—while the stars orbit each other. They’re calling the Jupiter-sized planets, tied in a strange, not-quite-sister relationship, “cousin planets.” Most known planets outside our solar system orbit stars that drift alone, like our Sun. Yet many stars are paired up in “binary” systems, twin stars formed from the same gas cloud, and which circle each other. Occasionally astronomers identify a planet that orbits an entire binary-star system, but researchers say this is the first case where each binary star seems to have its own separately orbiting world. The findings, around stars known as WASP-94A and WASP-94B, were made by a team of British, Swiss and Belgian astronomers. The British WASP-South survey, operated by Keele University in the U.K., found tiny dips in the light of the first star, suggesting that a Jupiter-like planet was passing in front of it. Swiss astronomers then found evidence for planets around both stars. “We observed the other star by accident, and then found a planet around that one also!” said Marion Neveu-VanMalle of Geneva Observatory, who wrote a paper on the findings. The planets are of a type known as “Hot Jupiters,” which orbit so close to their suns that their “years” last only a few days. They are rare, the astronomers said, so it would be unlikely to find two such planets in the same star system by chance. Perhaps, they speculated, WASP-94 has just the right conditions for producing Hot Jupiters? If so, it could be an important system for studying their development. The existence of huge, Jupiter-size planets so near to their stars is a long-standing puzzle, since it is believed they can’t form near to the star, where it is far too hot. They must form much further out, where it is cool, then move closer, perhaps as a result of an interaction with another planet or star. The idea is that finding Hot Jupiters in two stars of a binary pair might allow us to study the processes that move the planets inward.