A curiosa falta de metano num exoplaneta

Estadão:
“Falta de metano em exoplaneta gigante intriga cientistas.
O planeta gigante GJ 436b, descoberto em 2004 e localizado a 33 anos-luz da Terra, na direção da constelação de leão, é uma anomalia: não tem quantidades apreciáveis de metano em sua atmosfera.
Metano é um componente comum de vários planetas do nossos Sistema Solar. Modelos teóricos de atmosferas planetárias sugerem que qualquer mundo dotado da mistura de hidrogênio, carbono e oxigênio em sua atmosfera e com temperaturas de até 700ºC deveriam contar com uma grande quantidade de metano e uma pequena quantidade de dióxido de carbono.
Com temperatura de cerca de 500ºC, GJ 436b é uma exceção. Segundo a Nasa, isso mostra a diversidade dos planetas encontrados fora do Sistema Solar, e a necessidade de mais estudos.”
Leiam mais, aqui.

Terra:
“De acordo com os cientistas, para seguir uma lógica, o GJ 436b deveria ter uma grande quantidade de metano e pouco monóxido de carbono. Mas as observações do Spitzer, que captou a luz do planeta em seis comprimentos de infravermelho, mostram justamente o contrário.”

NASA:
“This Planet Smells Funny”.

Space.com:
“A big, hot alien planet with almost no methane in its atmosphere continues to stump astronomers, who have long thought the gas was a common feature of such worlds.
In our solar system, the gas giants Jupiter, Saturn, Uranus and Neptune are all rich in methane. But when astronomers trained NASA’s Spitzer Space Telescope on the extrasolar planet GJ 436b, a Neptune-sized world around a star 33 light-years from Earth, they found almost none of the stuff.
“Methane should be abundant on a planet of this temperature and size, but we found 7,000 times less methane than what the models predict,”
(…)
Gas giant planets are not the only worlds that contain methane in their atmospheres. The gas is common on Earth and has been spotted on Mars. For Mars and the gas giants, the gas is not an indicator of life since it can form through geophysical and chemical processes.
On Earth, methane can be a sign of life since it can form naturally — bubbling up from the bottom of swamps as organic matter decays — or as a byproduct from cows, goats or other lifeforms.
Methane’s link to life on our planet has made it a sought-after gas on other planets, including distant Earth-sized planets, since its presence could be a potential sign of biological activity.
But the lack of methane in a gas-giant world like GJ 436b, which was expected to have the compound in spades, is still a mystery to be solved, researchers said.”

Space.com:
“Alien Planet Has Pretty Weird Atmosphere.
A Neptune-sized planet orbiting another star has one odd atmosphere – analysis has shown that it lacks methane, a common ingredient for many planets in our solar system and a possible signature of life.
The discovery was made after NASA’s Spitzer Space Telescope captured the extrasolar planet’s light in six infrared wavelengths, allowing researchers to analyze the components of the exoplanet’s atmosphere.
The results are puzzling because existing models suggest that carbon present in the exoplanet should be in the form of methane”