"Long before it's in the papers"
January 28, 2015


Solar system “packed with planets” looks like our own

Nov. 6, 2007
World Science staff

As­tro­no­mers say they have found a dis­tant so­lar sys­tem that looks more like ours than do any of the others known. Though it lacks any ev­i­dence of hab­it­a­ble worlds, they added, some might turn up there.

It’s the “first quin­tu­ple plan­e­tary sys­tem,” and may have as yet-unde­tected Earth-like plan­ets or hab­it­a­ble moons, said San Fran­cis­co State Un­ivers­ity as­tron­o­mer Deb­ra Fisch­er, a mem­ber of the re­search team.

In this di­a­gram, a plan­et or­bits the "hab­it­a­ble zone" around its sun, at right. The hab­it­a­ble zone is in­di­cat­ed in green. The white curved lines mark the es­ti­mat­ed or­bits of plan­ets. (Image cour­te­sy NA­SA/JPL-Cal­tech).

Two an­i­ma­tions follow (cour­te­sy NA­SA/JPL-Cal­tech):

The first "flies" view­ers from Earth to the new­est known member of the 55 Can­cri sys­tem. (Down­load quick­time videos: small, large, stream­ing). This be­gins with a view of our night sky and 55 Can­cri (flash­ing dot), 41 light-years away. It then zooms through our so­lar sys­tem, pass­ing as­ter­oids and plan­ets, un­til reach­ing 55 Can­cri's out­skirts. The first plan­et to ap­pear is the far­thest from the star – a gi­ant plan­et, prob­a­bly made of gas, four times as heavy as Ju­pi­ter. It or­bits the star eve­ry 14 years, si­m­i­lar to Ju­pi­ter's 12-year or­bit. Three in­ner plan­ets next ap­pear, the clos­et be­ing about 10 to 13 times the Earth's mass with a less-than-three-day or­bit. Zoom­ing out, the an­i­ma­tion then shows the sys­tem's new­est known mem­ber – a mas­sive plan­et, like­ly made of gas, wa­ter and rock, weigh­ing some 45 Earths and or­biting eve­ry 260 days. The plan­ets' col­ors were cho­sen to re­sem­ble those of our sys­tem. As­tro­no­mers don't know what they real­ly look like.

The sec­ond an­i­ma­tion flies us out to 55 Can­cri's hab­it­a­ble zone (green) and shows the es­ti­mated or­bits of its plan­ets com­pared to our own. (Down­load quick­time videos: small, large, stream­ing.) It starts by high­light­ing the sys­tem's new­est known member, which is the fourth out from the star and thought to lie in the hab­it­a­ble zone. As­tro­no­mers spec­u­late it might have moons with liq­uid wa­ter.

It seems to be “packed with plan­ets,” as ours is, she added. All the plan­ets de­tected there are much heav­i­er than Earth, she not­ed, which poses prob­lems for their hab­it­abil­ity. But Earth-sized plan­ets, prac­tic­ally un­de­tect­a­ble out­side our So­lar Sys­tem with cur­rent tech­nol­o­gy, could easily have gone un­no­ticed.

The find­ing “has me jump­ing out of my socks,” said Ge­off Mar­cy of the Un­ivers­ity of Cal­i­for­nia, Berke­ley, an­oth­er mem­ber of the re­search team. The group an­nounced the find­ings at a press con­fer­ence in Pas­a­de­na, Ca­lif. Tues­day.

The dis­cov­ery sug­gests so­lar sys­tems much like our own are com­mon, he added. “Our Milky Way gal­axy, with 200 bil­lion stars, con­tains bil­lions of plan­e­tary sys­tems—many as rich as our own,” he said. “We strongly sus­pect many of these har­bor Earth-like plan­ets.”

More than 250 plan­ets out­side our sys­tem are known, but most of them are in so­lar sys­tems or in ar­range­ments that would seem to make it hard for life to form there. 

A pos­si­ble ex­cep­tion was an­nounced last April with a re­port that a plan­et or­bit­ing the star Gliese 581 might be hab­it­a­ble. But as­tron­o­mers have be­gun de­bat­ing wheth­er that’s the case, ac­cord­ing to Fisch­er’s team. It’s very tricky to de­fine a star’s “hab­it­a­ble zone,” the re­gion around it with the right tem­per­a­tures for liq­uid wa­ter to ex­ist, Mar­cy said.

The new find­ings—involving the star 55 Can­cri, visi­ble with bi­no­cu­lars in the con­stella­t­ion Can­cer—do re­veal a hab­it­a­ble-zone plan­et, they added. But it seems too large for life as we know it to take root there: it weighs the equiv­a­lent of an es­ti­mat­ed 45 Earths, which sci­en­tists say would probably make it a gas gi­ant like Sat­urn, though smaller.

“Such plan­ets are probably not hab­it­a­ble,” Mar­cy said; but it might well have hab­it­a­ble moons that re­main to be found. “If there is a moon or­bit­ing this new, mas­sive plan­et, it might have pools of liq­uid wa­ter on a rocky sur­face,” said Fisch­er. The hab­it­a­ble-zone gi­ant is about as far from its star as Ve­nus is from the Sun; but it would be cool­er than Ve­nus be­cause the star is some­what smal­ler and fainter than ours, the re­search­ers added.

The oth­er plan­ets around 55 Can­cri, whose whole plan­e­tary co­te­rie took 18 years to dis­cov­er, are also giants, they said. Re­search­ers dis­cov­ered the worlds us­ing the Dop­pler tech­nique, in which a plan­et’s gravita­t­ional tug is de­tected by the wob­ble its gra­vity pro­duces in the par­ent star.

A key fea­ture of the new­found sys­tem is that most of its worlds have near-circular or­bits around the star, Fisch­er said. That’s im­por­tant be­cause it means they would­n’t suf­fer dras­tic tem­per­a­ture varia­t­ions at dif­fer­ent times of the year; rath­er, their tem­per­a­ture fluctua­t­ions would be more or less equiv­a­lent to those of our sea­sons. The 55 Can­cri sys­tem also re­sembles ours in terms of its ap­prox­i­mate size, the re­search­ers said. A pa­per on the find­ings is to ap­pear in The Astro­phy­si­cal Jour­nal.

* * *

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Homepage image: Artist's impression of an extrasolar (not in our solar system) planet orbiting a star. (Courtesy NASA)

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Astronomers have identified a distant solar system that they say looks more like ours than any found to date. Though it lacks any evidence of habitable worlds, they added, some might yet turn up there. It’s the “first quintuple planetary system,” and may have as yet-undetected Earth-like planets or habitable moons, said San Francisco State University astronomer Debra Fischer, a member of the research team. It seems to be “packed with planets,” as ours is, she added. All the planets detected there are much heavier than Earth, she noted, which poses problems for their habitability. But Earth-sized planets, practically undetectable outside our Solar System with current technology, could easily have gone unnoticed. The finding “has me jumping out of my socks,” said Geoff Marcy of the University of California, Berkeley, another member of the research team. The group announced the findings at a press conference in Pasadena, Calif. Tuesday. The discovery suggests solar systems much like our own are common, he added. “Our Milky Way galaxy, with 200 billion stars, contains billions of planetary systems—many as rich as our own,” he said. “We strongly suspect many of these harbor earth-like planets.” More than 250 planets outside our system are known, but most of them are in solar systems or in arrangements that would seem to make it hard for life to form there. A possible exception was announced last April with a report that a planet orbiting the star Gliese 581 might be habitable. But astronomers have begun debating whether that’s the case, according to Fischer’s team. It’s a very tricky to define a star’s “habitable zone,” the region around it with the right temperatures for liquid water to exist, Marcy said. The new findings—involving the star 55 Cancri, in the constellation Cancer—do reveal a star in the habitable zone, they added, but it seems too large for life as we know it to take root there. It weighs the equivalent of an estimated 45 Earths, which scientists say would probably make it a gas giant similar to Saturn, though smaller. “Such planets are probably not habitable,” Marcy said; but it might well have habitable moons that remain to be found. “If there is a moon orbiting this new, massive planet, it might have pools of liquid water on a rocky surface,” said Fischer. The habitable-zone giant is about at the same distance from its star as Venus is from the Sun, but it would be cooler than Venus because the star is somewhat smaller than our Sun, the researchers added. The other planets around 55 Cancri, whose whole planetary coterie took 18 years to discover, weigh five to 10 Earths, and are much colder, they said. Researchers discovered the worlds using the Doppler technique, in which a planet’s gravitational tug is detected by the wobble its gravity produces in the parent star. NASA and the National Science Foundation funded the research. A key feature of the newfound system is that most of its worlds have near-circular orbits around the star, Fischer said. That’s important because it means they wouldn’t suffer drastic temperature variations at different times of the year; rather, their temperature fluctuations would be more or less equivalent to those of our seasons.