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Atmosphere of a “super-Earth” analyzed—possible poisons turn up

March 30, 2005
Courtesy 
and World Science staff

The first suc­cess­ful de­tec­tion of gas­es in the at­mos­phere of a “su­per-Earth” re­veals signs of hy­dro­gen and he­li­um—poss­ibly along with some gas­es known to us as poi­sons, as­tro­no­mers are re­port­ing.

Not de­tected, on the oth­er hand, was wa­ter va­por.

Anartist’s im­pres­sion of the super-Earth 55 Can­cri e in front of its par­ent star. Us­ing ob­ser­va­tions made with the NA­SA/ESA Hub­ble Space Tel­e­scope and new an­a­lyt­ic soft­ware sci­en­tists were able to an­a­lyse the com­po­si­tion of its at­mos­phere. It was the first time this was pos­si­ble for a super-Earth, they said. (Cred­it: ESA/Hub­ble, M. Ko­rn­messer)


The study is meant to help shed light on some gen­er­al char­ac­ter­is­tics of “Su­per-Earths”—plan­ets, found in oth­er so­lar sys­tems, that are thought to be bas­ic­ally sol­id like Earth, though quite a bit larg­er. 

De­spite the size dif­fer­ences, Su­per-Earths are among the more Earth-like plan­ets de­tected in oth­er so­lar sys­tems, be­ing much smaller than the “gas gi­ant” plan­ets like Sat­urn. Su­per-Earths are al­so be­lieved to be the most com­mon plan­e­tary type in our gal­axy, though they’re not nec­es­sarily liv­a­ble.

The plan­et in the stu­dy, called 55 Can­cri e, is far too hot to sup­port life as we know it, weighs about as much as eight Earths and was at one time dubbed a “di­a­mond plan­et” due to a sup­posedly car­bon-rich make­up, though lat­er work cast some doubt on that.

One fa­vor­a­ble fea­ture of 55 Can­cri e: its at­mos­phere was eas­i­er to study com­pared to many Super-Earths.

The re­sults of that study pro­vide “a first in­sight in­to the at­mos­phere of a super-Earth,” said Gio­van­na Tinetti of Un­ivers­ity Col­lege Lon­don, one of the re­search­ers. “We now have clues as to what the plan­et is cur­rently like, how it might have formed and evolved, and this has im­por­tant im­plica­t­ions for 55 Can­cri e and oth­er super-Earths.”

The as­tro­no­mers drew con­clu­sions about the gas­es by an­a­lyz­ing “spec­tral fin­ger­prints,” or dis­tinc­tive fea­tures of the star­light pass­ing near the plan­et.

The find­ing is “the first time that we have been able to find the spec­tral fin­ger­prints that show the gas­es,” said An­ge­los Tsiaras, a doc­tor­al stu­dent at Un­ivers­ity Col­lege Lon­don, who co-developed an anal­y­sis tech­nique used in the stu­dy. “Our anal­y­sis… sug­gests that the plan­et has man­aged to cling on to a sig­nif­i­cant amount of hy­dro­gen and he­li­um from the neb­u­la [a cloud of gas and dust] from which it formed.”

The re­search­ers used the new anal­y­sis tech­niques on da­ta ga­thered by the Hub­ble Space Tel­e­scope. The re­sults are to be pub­lished in the As­t­ro­phys­i­cal Jour­nal.

55 Can­cri e has a year that lasts 18 hours and tem­per­a­tures on the sur­face are thought to reach around 2,000 de­grees C (al­most 4,000 F). The plan­et lies in a so­lar sys­tem around the star 55 Can­cri, al­so known as Co­per­ni­cus, which is in the Can­cer con­stella­t­ion and lies an es­ti­mat­ed 40 light-years from Earth. A light-year is the dis­tance light tra­vels in a year.

What made the anal­y­sis pos­si­ble is that the star is very bright.

In­tri­guing­ly, the da­ta al­so hinted at a sig­na­ture for hy­dro­gen cy­a­nide, a mark­er for car­bon-rich at­mos­pheres.

“Such an amount of hy­dro­gen cy­a­nide would in­di­cate an at­mos­phere with a very high ra­tio of car­bon to oxy­gen,” said co-invest iga­tor Oliv­ia Venot of Cath­o­lic Un­ivers­ity Leu­ven, known as KU Leu­ven, in Bel­gium. “It would sup­port the the­o­ry that this plan­et is in­deed car­bon rich and a very ex­ot­ic place,” added Jon­a­than Ten­ny­son, one of the re­search­ers, with Un­ivers­ity Col­lege Lon­don. “Although, hy­dro­gen cy­a­nide or prus­sic ac­id is highly poi­son­ous, so it is per­haps not a plan­et I would like to live on!”


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The first successful detection of gases in the atmosphere of a “super-Earth” reveals signs of hydrogen and helium—possibly along with some gases known to us as poisons, astronomers are reporting. Not detected, on the other hand, was water vapor. The study is intended to help shed light on some general characteristics of “Super-Earths” — planets in other solar systems that are thought to be basically solid like Earth, though quite a bit larger. Despite the size differences, Super-Earths are among the more Earth-like planets detected in other solar systems, being much smaller than the “gas giant” planets like Saturn. Super-Earths also thought to be the most common planetary type in our galaxy, though they’re not necessarily livable. The planet in the study, called 55 Cancri e, is far too hot to support life as we know it, weighs about as much as eight Earths and was at one time dubbed a “diamond planet” due to a supposedly carbon-rich makeup, though later work cast some doubt on that. One favorable feature of 55 Cancri e: its atmosphere was easier to study compared to many Super-Earths. The results of that study provide “a first insight into the atmosphere of a super-Earth,” said Giovanna Tinetti of University College London, one of the researchers. “We now have clues as to what the planet is currently like, how it might have formed and evolved, and this has important implications for 55 Cancri e and other super-Earths.” The astronomers drew conclusions about the gases by analyzing “spectral fingerprints,” or distinctive features of the starlight passing near the planet. The finding is “the first time that we have been able to find the spectral fingerprints that show the gases,” said Angelos Tsiaras, a doctoral student at University College London, who co-developed an analysis technique used in the study. “Our analysis… suggests that the planet has managed to cling on to a significant amount of hydrogen and helium from the nebula [a cloud of gas and dust] from which it formed.” The researchers used the new analysis techniques on data from the Hubble Space Telescope. The results are to be published in the Astrophysical Journal. 55 Cancri e has a year that lasts 18 hours and temperatures on the surface are thought to reach around 2,000 degrees Celsius (almost 4,000 Fahrenheit). The planet lies in a solar system around the star 55 Cancri, also known as Copernicus, which is in the Cancer constellation and lies an estimated 40 light-years from Earth. What made the analysis possible is that the star is very bright. Intriguingly, the data also hinted at a signature for hydrogen cyanide, a marker for carbon-rich atmospheres. “Such an amount of hydrogen cyanide would indicate an atmosphere with a very high ratio of carbon to oxygen,” said co-investigator Olivia Venot of Catholic University Leuven, known as KU Leuven, in Belgium. “It would support the theory that this planet is indeed carbon rich and a very exotic place,” added Jonathan Tennyson, one of the researchers, with University College London. “Although, hydrogen cyanide or prussic acid is highly poisonous, so it is perhaps not a planet I would like to live on!”