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Planet may be turning to dust

May 19, 2012
Courtesy of MIT
and World Science staff

As­tro­no­mers have de­tected what they say could be a plan­et that’s evap­o­rat­ing un­der the sear­ing heat of its par­ent star.

A long trail of de­bris, like a comet’s tail, seems to be fol­low­ing the plan­et in its or­bit around the star—stuff that could be re­mains of the plan­et it­self, ac­cord­ing to the re­search­ers. The sci­en­tists, from the Mas­sa­chu­setts In­sti­tute of Tech­nol­o­gy, NASA and else­whe­re, cal­cu­late that the plan­et may be gone with­in 100 mil­lion years.

The team found that the dusty plan­et cir­cles its par­ent star eve­ry 15 hours, one of the short­est plan­et or­bits ev­er ob­served. Such a short or­bit must be very tight and means, they said, that the the orange-hot par­ent star must be heat­ing the little world, not much larg­er than Mer­cury, to about 3,600 de­grees Fahr­en­heit or 2,000 Cel­sius.

They pro­pose that rocky ma­te­ri­al at the plan­et’s sur­face melts and evap­o­rates in such heat, form­ing thick clouds that drift off into space. “We think this dust is made up of sub­mi­cron-sized par­t­i­cles,” said Saul Rap­pa­port, a phys­i­cist at MIT who worked on the stu­dy. “It would be like look­ing through a Los An­ge­les smog.”

The group’s find­ings, pub­lished in The As­t­ro­phys­i­cal Jour­nal, are based on da­ta from the Kep­ler Ob­serv­a­to­ry, a space-based tel­e­scope that sur­veys more than 160,000 stars in the Milky Way. The ob­serv­a­to­ry records the bright­ness of each star at reg­u­lar in­ter­vals; sci­en­tists then an­a­lyze the da­ta for signs of new plan­ets out­side our own so­lar sys­tem.

As­tro­no­mers us­ing the Kep­ler sat­el­lite typ­ic­ally iden­ti­fy plan­ets around dis­tant stars by look­ing for reg­u­lar dips in a star’s bright­ness. For ex­am­ple, if a star dims eve­ry month, a plan­et might be cours­ing around the star month­ly; each time it gets in front of the star, it blocks the same small amount of light. But Rap­pa­port and col­leagues saw an odder light pat­tern from a star dubbed KIC 12557548, which lies about 1,500 light-years away. Its bright­ness dropped by dif­fer­ent in­tens­i­ties eve­ry 15 hours — as if some­thing were block­ing the star reg­u­larly, but by var­y­ing de­grees.

The team con­sid­ered sev­eral ex­plana­t­ions, in­clud­ing that two plan­ets might be or­biting each oth­er while al­so or­biting the star as a pair. But that idea was re­jected on grounds that plan­ets or­biting a star so closely would lack suf­fi­cient room to al­so or­bit each oth­er.

The sci­en­tists then came up with the notion that that the var­y­ing in­tens­i­ties of light were caused by a some­what amor­phous, shape-shifting body. “I’m not sure how we came to this epiphany,” Rap­pa­port said. “But it had to be some­thing that was fun­da­men­tally chang­ing. It was not a sol­id body, but rath­er, dust com­ing off the plan­et.”

Rap­pa­port and col­leagues in­ves­t­i­gated var­i­ous ways in which dust could be cre­at­ed and blown off a plan­et. They rea­soned that the plan­et must have a low gravita­t­ional field, much like that of Mer­cu­ry, in or­der for gas and dust to es­cape from the plan­et’s gravita­t­ional pull. The plan­et must al­so be ex­tremely hot.

Rap­pa­port said there are two pos­si­ble ways plan­etary dust might form: it could erupt as ash from vol­ca­noes, or it might arise from met­als that va­por­ize, then con­dense in­to dust. The re­search­ers cre­at­ed a mod­el of the plan­et or­biting its star, along with a long, trail­ing dust cloud. The dust was thick­est right around the plan­et, thin­ning out as it trailed away. The group sim­u­lat­ed the star’s bright­ness as the plan­et and its dust cloud passed by, and found that the light pat­terns matched those seen.

“We’re ac­tu­ally now very hap­py about the asym­me­try in the eclipse pro­file,” that is, the dim­ming patterns, Rap­pa­port said. “At first we did­n’t un­der­stand this pic­ture. But once we de­vel­oped this the­o­ry, we real­ized this dust tail has to be he­re. If it’s not, this pic­ture is wrong.”

Dan Fab­rycky, a mem­ber of the Kep­ler Ob­serv­a­to­ry sci­ence team, said the mod­el may add to the many dif­fer­ent ways in which a plan­et can dis­ap­pear. “This might be anoth­er way in which plan­ets are even­tu­ally doomed,” said Fab­rycky, who was not in­volved in the re­search. “A lot of re­search has come to the con­clu­sion that plan­ets are not eter­nal ob­jects, they can die ex­tra­or­di­nary deaths.”


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Astronomers have detected what they say could be a planet that’s evaporating under the searing heat of its parent star. A long trail of debris, like a comet’s tail, seems to be following the planet in its orbit around the star—stuff that could be remains of the planet itself, according to the researchers. The scientists, from the Massachusetts Institute of Technology, NASA and elsewhere, calculate that the planet may be gone within 100 million years. The team found that the dusty planet circles its parent star every 15 hours, one of the shortest planet orbits ever observed. Such a short orbit must be very tight and implies that the planet must be heated by its orange-hot parent star to a temperature of about 3,600 degrees Fahrenheit, the scientists said. They propose that rocky material at the surface of the planet melts and evaporates at such high temperatures, forming a wind that carries both gas and dust into space. Dense clouds of the dust trail the planet as it speeds around its star. “We think this dust is made up of submicron-sized particles,” said Saul Rappaport, a physicist at MIT who worked on the study. “It would be like looking through a Los Angeles smog.” The group’s findings, published in the Astrophysical Journal, are based on data from the Kepler Observatory, a space-based telescope that surveys more than 160,000 stars in the Milky Way. The observatory records the brightness of each star at regular intervals; scientists then analyze the data for signs of new planets outside our own solar system. Astronomers using the Kepler satellite typically identify planets around distant stars by looking for regular dips in a star’s brightness. For example, if a star dims every month, one possibility is that the dimming is due to a planet that travels around the star over the course of a month; each time the planet travels in front of the star, the planet blocks the same small amount of light. Rappaport and his colleagues came across a curious light pattern from a star dubbed KIC 12557548, which lies about 1,500 light-years away. They found that its brightness dropped by different intensities every 15 hours — suggesting that something was blocking the star regularly, but by varying degrees. The team considered several explanations for the puzzling data, including the possibility that two planets were orbiting each other while also orbiting the star as a pair. But that scenario was tossed out on grounds that planets orbiting a star so closely would lack sufficient room to also orbit each other. The scientists then came up with the idea that that the varying intensities of light were caused by a somewhat amorphous, shape-shifting body. “I’m not sure how we came to this epiphany,” Rappaport said. “But it had to be something that was fundamentally changing. It was not a solid body, but rather, dust coming off the planet.” Rappaport and colleagues investigated various ways in which dust could be created and blown off a planet. They reasoned that the planet must have a low gravitational field, much like that of Mercury, in order for gas and dust to escape from the planet’s gravitational pull. The planet must also be extremely hot — on the order of 3,600° F. Rappaport said there are two possible explanations for how the planetary dust might form: It might erupt as ash from surface volcanoes, or it could form from metals that are vaporized by high temperatures and then condense into dust. The researchers created a model of the planet orbiting its star, along with a long, trailing cloud of dust. The dust was thickest right around the planet, thinning out as it trailed away. The group simulated the star’s brightness as the planet and its dust cloud passed by, and found that the light patterns matched the observed light patterns. “We’re actually now very happy about the asymmetry in the eclipse profile,” Rappaport said. “At first we didn’t understand this picture. But once we developed this theory, we realized this dust tail has to be here. If it’s not, this picture is wrong.” Dan Fabrycky, a member of the Kepler Observatory science team, said the model may add to the many different ways in which a planet can disappear. “This might be another way in which planets are eventually doomed,” said Fabrycky, who was not involved in the research. “A lot of research has come to the conclusion that planets are not eternal objects, they can die extraordinary deaths, and this might be a case where the planet might evaporate entirely in the future.”