"Long before it's in the papers"
May 05, 2015


First evidence of changes on a “super-Earth” reported

May 5, 2015
Courtesy of the University of Cambridge
and World Science staff

Re­search­ers say they have for the first time de­tected at­mos­pher­ic changes on a rocky plan­et out­side the so­lar sys­tem, meas­ur­ing a nearly three­fold change in tem­per­a­ture over two years. 

The cause is still un­der in­ves­ti­ga­t­ion; mas­sive vol­can­ic ac­ti­vity is one pos­si­bil­ity, re­search­ers say. The plan­et was once thought to be made of dia­mond, but as­tro­no­mers are moving away from that theory.

Artist’s im­pres­sion of su­per-Earth 55 Can­cri e, show­ing a hot par­tially-molten sur­face of the plan­et before and after poss­ible volca­nic activity on the day side. (Cre­dit: NASA/JPL-Cal­tech/R. Hurt)

Plan­ets like the one be­ing stud­ied, called 55 Can­cri e, are called “super-Earths” be­cause they’re be­lieved to some­what Earth-like in their make­up, but big­ger. As­tro­no­mers de­tect big plan­ets more of­ten than small ones be­cause the big­ger ones are eas­i­er to find. 

The abil­ity to peek in­to the at­mo­spheres of ‘super-Earths’ marks an im­por­tant mile­stone to­wards iden­ti­fy­ing hab­it­a­ble plan­ets out­side the so­lar sys­tem, astro­n­om­ers say.

Us­ing NASA’s Spitzer Space Tel­e­scope, they ob­served light com­ing from the plan­et, which or­bits a Sun-like star lo­cat­ed 40 light-years away in the Can­cer con­stella­t­ion. A light-year is the dis­tance light trav­els in a year. 

Tem­per­a­tures on the hot “day” side of the plan­et, fac­ing its sun, were meas­ured as swing­ing be­tween 1,000 and 2,700 de­grees Cel­si­us.

“This is the first time we’ve seen such dras­tic changes in light emit­ted from an exoplan­et,” or plan­et out­side our so­lar sys­tem, said Nikku Mad­husud­han of the Uni­vers­ity of Cam­bridge, co-au­thor of a re­port on the find­ings.

The re­search­ers think the vari­abil­ity might be due to huge plumes of gas and dust that some­times blan­ket the sur­face, which may be par­tially mol­ten due to vol­can­ism. That would sug­gest more vol­can­ic ac­ti­vity than on Io, one of Ju­pi­ter’s moons and the most ge­o­log­ic­ally ac­tive body in the so­lar sys­tem.

“We saw a 300 per­cent change in the sig­nal com­ing from this plan­et, which is the first time we’ve seen such a huge lev­el of vari­abil­ity in an exo­plan­et,” said Brice-Olivier De­mory of the uni­vers­ity, lead au­thor of the new stu­dy. “While we can’t be en­tirely sure, we think a likely ex­plana­t­ion for this vari­abil­ity is large-scale sur­face ac­ti­vity, pos­sibly vol­can­ism, on the sur­face is spew­ing out mas­sive vol­umes of gas and dust, which some­times blan­ket the ther­mal [heat] emis­sion from the plan­et so it is not seen from Earth.”

55 Can­cri e is be­lieved to be rocky and about twice the size and eight times the weight of Earth. It is one of five plan­ets or­bit­ing its sun, which is so close that a year lasts just 18 hours. The plan­et is al­so tid­ally locked, mean­ing it does­n’t spin like Earth­—in­stead there are per­ma­nent day and night sides. It is the near­est super-Earth whose at­mos­phere can be stud­ied.

Most of the early re­search on exo­plan­ets has been on gas gi­ants si­m­i­lar to Ju­pi­ter and Sat­urn, since their enor­mous size makes them eas­i­er to find. In re­cent years, as­tro­no­mers have been able to map the con­di­tions on many of these gas gi­ants, but it is much harder to do so for super-Earths, which can weigh up to 10 times Earth.

Ear­li­er ob­serva­t­ions of 55 Can­cri e point­ed to an abun­dance of car­bon, sug­gesting the plan­et was made of dia­mond. But the new re­sults have mud­died those ear­li­er ob­serva­t­ions con­sid­erably and opened new ques­tions, ac­cord­ing to the in­ves­ti­ga­tors.

“When we first iden­ti­fied this plan­et, the mea­sure­ments sup­ported a car­bon-rich mod­el,” said Mad­husud­han. “But now we’re find­ing that those mea­sure­ments are chang­ing in time. The plan­et could still be car­bon rich, but now we’re not so sure—ear­li­er stud­ies of this plan­et have even sug­gested that it could be a wa­ter world. The pre­s­ent vari­abil­ity is some­thing we’ve nev­er seen an­y­where else, so there’s no ro­bust con­ven­tion­al ex­plana­t­ion. But that’s the fun in sci­ence—clues can come from un­ex­pected quar­ters. The pre­s­ent ob­serva­t­ions open a new chap­ter in our abil­ity to study the con­di­tions on rocky exo­plan­ets us­ing cur­rent and upcom­ing large tele­scopes.”

The study is ap­pears May 5 on­line in the jour­nal Monthly No­tices of the Roy­al As­tro­nom­i­cal So­ci­e­ty.

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For the first time, researchers have detected atmospheric changes on a rocky planet outside the solar system, measuring a nearly threefold change in temperature over two years. The cause is still under investigation; massive volcanic activity is one possibility, researchers say. The planet was once thought to be made of diamond, but astronomers are less sure about that now. Planets like the one being studied, called 55 Cancri e, are called “super-Earth” because they’re believed to somewhat Earth-like in their makeup, but bigger. Astronomers detect big planets more often than small ones because the bigger ones are easier to find. But the ability to peek into the atmospheres of ‘super-Earths’ marks an important milestone towards identifying habitable planets outside the solar system, they say. Using NASA’s Spitzer Space Telescope, they observed light coming from the planet, which orbits a Sun-like star located 40 light-years away in the Cancer constellation. A light-year is the distance light travels in a year. Temperatures on the hot “day” side of the planet, facing the sun, were measured as swinging between 1,000 and 2,700 degrees Celsius. “This is the first time we’ve seen such drastic changes in light emitted from an exoplanet,” or planet outside our solar system, said Nikku Madhusudhan of the University of Cambridge, a co-author on the new study. The researchers think the variability might be due to huge plumes of gas and dust that sometimes blanket the surface, which may be partially molten due to volcanism. That would suggest more volcanic activity than on Io, one of Jupiter’s moons and the most geologically active body in the solar system. “We saw a 300 percent change in the signal coming from this planet, which is the first time we’ve seen such a huge level of variability in an exoplanet,” said Brice-Olivier Demory of the university, lead author of the new study. “While we can’t be entirely sure, we think a likely explanation for this variability is large-scale surface activity, possibly volcanism, on the surface is spewing out massive volumes of gas and dust, which sometimes blanket the thermal [heat] emission from the planet so it is not seen from Earth.” 55 Cancri e is believed to be rocky and about twice the size and eight times the weight of Earth. It is one of five planets orbiting its sun, which is so close that a year lasts just 18 hours. The planet is also tidally locked, meaning it doesn’t spin like Earth—instead there are permanent day and night sides. Since it is the nearest super-Earth whose atmosphere can be studied, 55 Cancri e is among the best candidates for detailed observations of surface and atmospheric conditions on rocky exoplanets. Most of the early research on exoplanets has been on gas giants similar to Jupiter and Saturn, since their enormous size makes them easier to find. In recent years, astronomers have been able to map the conditions on many of these gas giants, but it is much harder to do so for super-Earths, which can weigh up to 10 times Earth. Earlier observations of 55 Cancri e pointed to an abundance of carbon, suggesting the planet was made of diamond. But these new results have muddied those earlier observations considerably and opened new questions, according to the investigators. “When we first identified this planet, the measurements supported a carbon-rich model,” said Madhusudhan. “But now we’re finding that those measurements are changing in time. The planet could still be carbon rich, but now we’re not so sure—earlier studies of this planet have even suggested that it could be a water world. The present variability is something we’ve never seen anywhere else, so there’s no robust conventional explanation. But that’s the fun in science—clues can come from unexpected quarters. The present observations open a new chapter in our ability to study the conditions on rocky exoplanets using current and upcoming large telescopes.” The study is to appear May 5 online in the journal Monthly Notices of the Royal Astronomical Society.