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Photo captures three planets by distant sun

Nov. 13, 2008
World Science staff

The tech­nol­o­gy for pho­tograph­ing plan­ets in dis­tant so­lar sys­tems is mak­ing strides, as­tro­no­mers say, with new im­ages in­clud­ing one that shows three worlds around a young star.

As­t­ro­phys­i­cist Chris­tian Marois and col­leagues said they found the plan­ets—which appeared as tiny dots by the star HR 8799—using the Keck and Gem­i­ni North tele­scopes on Mau­na Kea in Ha­waii. 

A­bove, a di­rect im­age of the star HR 8799. Be­low, the image af­ter com­put­er pro­cess­ing, which re­duces the star­light to a bunch of speck­les and al­lows three pre­sumed plan­ets to ap­pear as faint red dots around the star at about 2:00, 5:00 and 10:00 o'­clock. The im­ages were tak­en in in­fra­red light with the Keck tel­e­scope, and the bot­tom im­age co­vers the same ar­ea as shown in the box in the top im­age. (Cour­te­sy Na­tion­al Re­search Coun­cil Can­a­da) 


Be­fore now, as­tro­no­mers had re­ported pho­tograph­ing just one plan­et of a star oth­er than our sun. Oth­er de­tec­tions of such ob­jects had been done through stu­dy­ing their gravita­t­ional ef­fects rath­er than through im­ag­ing, which is dif­fi­cult be­cause the star­light tends to over­whelm any light from the plan­ets.

Mem­bers of Marois’ group said they de­vel­oped an ad­vanced com­put­er pro­cess­ing meth­od that helped dis­tin­guish the plan­ets from the star­light. Their find­ings ap­pear in the Nov. 13 is­sue of Sci­ence Ex­press, the ad­vance on­line edi­tion of the re­search jour­nal Sci­ence.

HR 8799 is just vis­i­ble to the un­aided eye and lies about 130 light-years from Earth in the di­rec­tion of the con­stella­t­ion Peg­a­sus, in the north­ern sky. A light-year is the dis­tance light trav­els in a year.

These plan­ets, about 60 mil­lion years old, are young enough that they are still glow­ing from heat left over from their forma­t­ion, said the re­search­ers, led by Marois, of the Na­tional Re­search Coun­cil of Can­a­da Herzberg In­sti­tute of As­t­ro­phys­ics in Vic­to­ria, Brit­ish Co­lum­bia.

The worlds seem to be around sev­en, ten, and ten times the weight of Ju­pi­ter and some­what wid­er, they added. But these es­ti­mates are rough, the group not­ed, be­cause the speed of the plan­ets’ or­bit, which would yield the best meas­ure of weight, is un­known.

“Com­par­i­son with the­o­ret­i­cal mod­el at­mo­spheres con­firms that all three plan­ets pos­sess com­plex at­mo­spheres with dusty clouds par­tially trap­ping and re-radiating the es­cap­ing heat,” said Travis Bar­man, an as­tron­o­mer at Low­ell Ob­serv­a­to­ry at the Uni­ver­s­ity of Cal­i­for­nia Los An­ge­les, a co-author of the stu­dy.

Fur­ther stud­ies of the light emis­sions from the plan­ets will let re­search­ers study their make­up in de­tail, he added. The plan­ets are meas­ured to lie up to 70 times furth­er from their sun than the Earth does from ours.

Sep­a­rate­ly, anoth­er re­search team im­aged a plan­et or­bit­ing the star Fo­mal­haut, one of the bright­est in the sky and just 25 light years from Earth. These are the first snap­shots of a plan­et out­side our so­lar sys­tem tak­en in vis­i­ble light rath­er than in oth­er forms of light not vis­i­ble to hu­man eyes, said Uni­ver­s­ity of Cal­i­for­nia, Berke­ley, as­tron­o­mer Paul Kalas, co-author of a pa­per on the find­ings. That re­port al­so ap­pears in the Nov. 13 Sci­ence Ex­press.


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The technology for photographing planets in distant solar systems is making strides, astronomers say, with new images including one that shows three planets around a young star. Astrophysicist Christian Marois and colleagues said they used the Keck and Gemini North telescopes on Mauna Kea in Hawaii to find the three planets orbiting the star HR 8799. Before now, astronomers had reported photographing just one planet of a star other than our sun. Other detections of such objects had been done through studying their gravitational effects rather than through imaging, which is difficult because the starlight tends to overwhelm any light from the planets. Members of Marois’ group said they developed an advanced computer processing method that helped distinguish the planets from the starlight. Their findings appear in the Nov. 13 issue of Science Express, in the advance online edition of the research journal Science. HR 8799 is just visible to the unaided eye and lies about 130 light-years from Earth in the direction of the constellation Pegasus, in the northern sky. A light-year is the distance light travels in a year. These planets, about 60 million years old, are young enough that they are still glowing from heat left over from their formation, said the researchers, led by Marois, of the National Research Council of Canada Herzberg Institute of Astrophysics in Victoria, British Columbia. The worlds seems to be around seven, ten, and ten times the weight of Jupiter and somewhat wider, they added. But these estimates are rough, the group noted, because the speed of the planets’ orbit, which would yield the best measure of weight, is unknown. “Comparison with theoretical model atmospheres confirms that all three planets possess complex atmospheres with dusty clouds partially trapping and re-radiating the escaping heat,” said Travis Barman, an astronomer at Lowell Observatory at the University of California Los Angeles, a co-author of the study. Further studies of the light emissions from the planets will let researchers study their makeup in detail, he added. Separately, another research team imaged a planet orbiting the star Fomalhaut, one of the brightest in the sky and just 25 light years from Earth. These are the first snapshots of a planet outside our solar system taken in visible light rather than in other forms of light not visible to human eyes, said University of California, Berkeley, astronomer Paul Kalas, co-author of a paper on the findings. That report also appears in the Nov. 13 Science Express.