Mighty Dons Of Science News

As­tro­no­mers have re­ported find­ing as many as six plan­ets, not many times heav­i­er than Earth, or­bit­ing two near­by Sun-like stars.
The ob­jects, which in­clude two that are about 5 and 7.5 times as heavy as Earth, are rais­ing sci­en­tists’ hopes that it will be just a few years that plan­ets very much like ours turn up.

Image from a sci­en­tists' an­i­ma­tion of the 5-Earth-mass plan­et 61 Vir B, or­bit­ing the star 61 Vir­gi­nis. This plan­et moves in a tight, 4-day or­bit around its star. Half of the plan­et sur­face is much hot­ter than the oth­er half be­cause one side al­ways faces the star. (Cour­tesy U. Hert­ford­shire)

The re­search­ers, led by Ste­ven Vogt of the Un­ivers­ity of Cal­i­for­nia, San­ta Cruz, and Paul But­ler of the Car­ne­gie In­sti­tu­tion of Wash­ing­ton, said the two “super-Earths” are the first ones found around Sun-like stars.

“These de­tec­tions in­di­cate that low-mass plan­ets are quite com­mon around near­by stars. The dis­cov­ery of po­ten­tially hab­it­a­ble near­by worlds may be just a few years away,” said Vogt. As­tro­no­mers claim they’re over­com­ing past dif­fi­cul­ties in find­ing smaller plan­ets, which are more like ours in size and are con­sid­ered like­li­er to be hab­it­a­ble than large plan­ets.

The team found the new plan­et sys­tems by com­bin­ing da­ta gath­ered at the W. M. Keck Ob­serv­a­to­ry in Ha­waii and the An­glo-Aus­tral­ia Tel­e­scope in New South Wales, Aus­tral­ia. Two pa­pers de­scrib­ing the new plan­ets have been ac­cept­ed for pub­lica­t­ion in the As­t­ro­phys­i­cal Jour­nal.

Three of the new plan­ets or­bit the bright star 61 Vir­gi­nis, vis­i­ble with the na­ked eye un­der dark skies in the Spring con­stella­t­ion Vir­go. Space sci­en­tists have long been fas­ci­nat­ed with this star, which is a re­la­tive­ly close 28 light years away (a light year is the dis­tance light trav­els in a year). Among hun­dreds of our near­est stel­lar neigh­bors, 61 Vir stands out as be­ing the most nearly si­m­i­lar to the Sun in terms of age, mass, and oth­er es­sen­tial prop­er­ties.

Vogt and col­leagues have found that 61 Vir hosts at least three plan­ets, weigh­ing in the range of about 5 to 25 Earths. All would be ex­treme­ly hot, though, as they are well with­in orbits equi­va­lent to that of Ve­nus.

Re­cent­ly, a sep­a­rate team of as­tro­no­mers used NASA’s Spitzer Space Tel­e­scope to dis­cov­er that 61 Vir al­so con­tains a thick ring of dust at a dis­tance roughly twice as far from 61 Vir as Plu­to is from our Sun. The dust is ap­par­ently cre­at­ed by col­li­sions of comet-like bod­ies in the cold out­er reaches of the sys­tem.

“Spitzer’s de­tec­tion of cold dust or­bit­ing 61 Vir in­di­cates that there’s a real kin­ship be­tween the Sun and 61 Vir,” said Eu­ge­nio Ri­ve­ra of the Un­ivers­ity of Cal­i­for­nia, San­ta Cruz. Ri­ve­ra com­put­ed an ex­ten­sive set of sim­ula­t­ions to find that a hab­it­a­ble Earth-like world could easily ex­ist in the as-yet un­ex­plored re­gion be­tween the newly dis­cov­ered plan­ets and the out­er dust disk.

Ac­cord­ing to Vogt, the plan­etary sys­tem around 61 Vir is an ex­cel­lent can­di­date for study by the new Au­to­mat­ed Plan­et Find­er Tel­e­scope re­cently con­structed at Lick Ob­serv­a­to­ry on Mount Ham­il­ton near San Jose, Ca­lif. “Need­less to say, we’re very ex­cit­ed to con­tin­ue mon­i­tor­ing this sys­tem” us­ing that de­vice, said Vogt, who is the prin­ci­pal in­ves­ti­ga­tor for the tel­e­scope.

The sec­ond new sys­tem found by the team fea­tures a plan­et weigh­ing the equiv­a­lent of about 7.5 Earths and or­bit­ing the star HD 1461, anoth­er near per­fect twin of the Sun about 76 light-years away. The plan­et, des­ig­nat­ed HD 1461b, is about half­way be­tween Earth and Ura­nus in weight. The re­search­ers said they can­not tell yet if it’s a scaled-up ver­sion of Earth, com­posed largely of rock and iron, or wheth­er, like Ura­nus and Nep­tune, it is made mostly of wa­ter.

At least one and pos­sibly two ad­di­tion­al plan­ets al­so or­bit the star, the group said. Ly­ing in the con­stella­t­ion Ce­tus, HD 1461 can be seen with the na­ked eye in the early eve­ning un­der good dark-sky con­di­tions.

The Lick Car­ne­gie Exoplan­et Sur­vey Team led by Vogt and But­ler uses ve­locity mea­sure­ments from ground-based tel­e­scopes to de­tect the “wob­ble” in­duced in a star by the gravita­t­ional tug of an or­bit­ing plan­et. In the past year, im­prov­ing meth­ods have made it ev­i­dent that plan­ets or­bit­ing the Sun’s near­est neigh­bors are ex­tremely com­mon: cur­rent in­dica­t­ions are that fully half of near­by stars have a de­tectable plan­et with mass equal to or less than Nep­tune’s, But­ler said.

The Lick-Car­ne­gie Exoplan­et Sur­vey Team has de­vel­oped a pub­licly avail­a­ble tool, the Sys­tem­ic Con­sole, which en­ables mem­bers of the pub­lic to search for the sig­nals of ex­tra­so­lar plan­ets by ex­plor­ing real da­ta sets. This tool is avail­a­ble on­line at www.ok­lo.org.