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Strongest evidence yet that planets form from disks claimed

Oct. 9, 2006
Special to World Science  

A new study has pro­vid­ed what as­tronomers call the strong­est ev­i­dence yet for what the phi­los­o­pher Em­man­u­el Kant and sci­en­tists have long pre­dicted: plan­ets form from de­bris disks around stars.

Artist's con­cept of the Ep­si­lon Erid­a­ni sys­tem. (Cour­te­sy NA­SA, ESA, and G. Ba­con [STScI])


Kant, a German, first pro­posed more than two cen­tu­ries ago that plan­ets are born from disks of dust and gas that swirl around their home stars. 

As­tronomers have re­ported de­tec­tions of more than 200 ex­tra­so­lar plan­ets, and many de­bris disks around young stars. But they have yet to iden­ti­fy a plan­et and disk around the same star. 

In the new study, re­search­ers using the Hub­ble Space Tel­e­scope and ground-based ob­ser­va­to­ries said they found such a sys­tem. 

The as­tro­no­mers, led by G. Fritz Ben­e­dict and Bar­ba­ra Mc­Ar­thur of the Uni­ver­si­ty of Tex­as, Aus­tin, said the plan­et is aligned with the disk, called a cir­cum­stel­lar disk. 

First de­tected six years ago, the world or­bits the near­by Sun-like star Ep­si­lon Erid­a­ni, 10.5 light-years from Earth in the di­rec­tion of the con­stel­la­tion Erid­a­nus. A light-year is the dis­tance light trav­els in a year. The body is al­so the near­est known plan­et to us out­side our so­lar sys­tem.

The plan­et’s or­bit is tilted 30 de­grees to Earth, the same an­gle at which the star’s disk is tilted, re­search­ers said. The re­sults are to ap­pear in the No­vem­ber is­sue of the As­tro­nom­i­cal Jour­nal. The re­search­ers al­so used the Hub­ble ob­ser­va­tions to get a more pre­cise es­ti­mate of the world’s mass, which they cal­cu­lat­ed as 1.5 times that of Ju­pi­ter.

The as­tronomers cal­cu­lat­ed the mass and or­bit of the plan­et, des­ig­nat­ed HD22049, by meas­ur­ing the star’s lo­ca­tion as it wob­bled on the sky, a tech­nique called as­trom­e­try. The slight wob­bles are caused by the grav­i­ta­tion­al tug of the un­seen plan­et, like a small dog pulling its mas­ter on a leash.


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A new study has provided what astronomers call most solid evidence yet for what the philosopher Emmanuel Kant and scientists have long predicted: planets form from debris disks around stars. More than two centuries ago, Kant first proposed that planets are born from disks of dust and gas that swirl around their home stars. Astronomers have reported detections of more than 200 extrasolar planets, and many debris disks around young stars. But they have yet to find a planet and a debris disk around the same star. The new study used the Hubble Space Telescope and ground-based observatories. The astronomers, led by G. Fritz Benedict and Barbara McArthur of the University of Texas, Austin, reported the planet is aligned with the disk, called a circumstellar disk. Detected six years ago, the world orbits the nearby Sun-like star Epsilon Eridani, located 10.5 light-years from Earth in the direction of the constellation Eridanus. A light-year is the distance light travels in a year. The body is also the nearest known planet to us outside our solar system. The planet’s orbit is tilted 30 degrees to Earth, the same angle at which the star’s disk is tilted, researchers said. The results are to appear in the November issue of the Astronomical Journal. The researchers also used the Hubble observations to get a more precise estimate of the planet’s mass, which they calculated as 1.5 times that of Jupiter. The astronomers calculated the mass and orbit of the planet, designated HD22049, by measuring the star’s location as it wobbled on the sky, a technique called astrometry. The slight wobbles are caused by the gravitational tug of the unseen planet, like a small dog pulling its master on a leash.