Gliese 581 g – o primeiro planeta como a Terra?

Ainda há uns dias atrás, previa-se que um planeta como a Terra seria descoberto nos próximos meses.
Segundo a maior parte dos especialistas consultados, esse planeta foi encontrado esta semana.

Chama-se Gliese 581g, e é o 6º planeta a ser descoberto à volta da estrela Gliese 581.

Gliese 581 é uma estrela anã vermelha que se encontra a cerca de 20 anos-luz da Terra.
Sendo anã vermelha, então a chamada Zona Habitável é mais perto da estrela, ou seja, os planetas terão que estar mais perto da estrela (que a Terra do Sol) para poderem ter água no estado líquido na sua superfície e até terem vida.
(o Gliese 581f está na nossa Zona Habitável, ou seja, se estivesse em órbita de uma estrela como o Sol, estaria na Zona Habitável. Mas como a estrela é uma anã vermelha, então Gliese 581f está longe, mas Gliese 581g está mesmo na Zona Habitável dessa estrela)

Já no passado parecia que essa estrela tinha planetas na Zona Habitável, com as descobertas de Gliese 581d e Gliese 581e (leiam este nosso post), mas desta vez parece ser mesmo verdade.

Não só deverá ter água líquida na superfície, mas abre a possibilidade de ter vida.
E nós, humanos, até já enviamos mensagens para esse planeta. Foi o site social BEBO que enviou essas mensagens em Outubro de 2008, como podem ler aqui, aqui, e aqui. Daqui por 18 anos, eles recebem as mensagens, e 40 anos após o envio das mensagens (em 2048), nós vamos ter a resposta (se eles forem inteligentes, tiverem rádio-telescópios, e estiverem a ouvir nesta direcção).
Podem também ler aqui, que, em 2009, o astroPT também já enviou uma mensagem para essa estrela, através da revista Cosmos. Se os extraterrestres receberem essa mensagem, e nos responderem (ao astroPT), vamos receber essa mensagem em 2050.
😛
(claro isto é especulação… e humor)

Leiam o post do Luis Lopes, aqui no blog, sobre este assunto.
O planeta terá 3 vezes a massa da Terra, será praticamente do tamanho da Terra (só um pouco maior), tem uma gravidade praticamente igual à Terra (pouco superior), orbita a estrela em 37 dias (é o ano do planeta), está a 0.15 AU da estrela-mãe, é rochoso como a Terra, tem uma atmosfera, tem temperaturas moderadas (uma média de -31ºC a -12ºC, mas como é uma média, então em alguns locais será mais quente), deverá ter água líquida à superfície (lagos nas zonas mais quentes, com temperaturas superiores a 0ºC), e poderá ter, quiçá, vida tal como a conhecemos.
O planeta roda à mesma velocidade com que orbita a estrela, o que faz com que mostre sempre o mesmo lado para a sua estrela (tal como a Lua mostra sempre o mesmo lado para nós). Isso faz com que um dos lados será quente (máxima de 70ºC), e o outro lado será frio (mínima de -40ºC). A diferença não é enorme, porque a atmosfera estabiliza mais a temperatura. Ou seja, entre uma zona e outra, deverá existir uma temperatura moderada.

Gliese 581g está no sítio certo – comparando com o nosso sistema solar, será uma Terra.
Gliese 581c é o planeta dentro da Zona Habitável, mais perto da estrela – comparando com o nosso sistema solar, será Vénus.
Gliese 581d é o planeta dentro da Zona Habitável, mais longe da estrela – comparando com o nosso sistema solar, será Marte.

(Gliese 581g estará a meio, entre Gliese 581c e Gliese 581d)

Além do mais, as órbitas dos planetas são praticamente circulares.
Tal como os planetas no nosso sistema solar.

É um sistema solar, como o nosso.

E como a maioria das estrelas são anãs vermelhas, então esta notícia faz crescer exponencialmente a quantidade de possíveis “Terras” no Universo.

Esta notícia fenomenal está a ser divulgada com estrondo, como não poderia deixar de ser.
No entanto, aconselho calma… porque, para já, este é somente um planeta-candidato: ou seja, para já ainda não temos confirmação da existência do planeta.

Público:
“Planetas rochosos, parecidos com a Terra, já foram descobertos. Mas este, a 20 anos-luz de distância de nós, é o primeiro que parece ser habitável, dizem cientistas norte-americanos.”

Ionline:
“Encontrado planeta com “100% de hipóteses de ter vida”.
Chama-se Gliese 581g, está a 20 anos-luz da Terra na constelação de Balança e, de acordo com uma publicação do Astrophysical Journal, apresenta todas as características básicas para ser habitável.
O planeta foi descoberto por um grupo de astrónomos da Universidade da Califórnia em Santa Cruz (UCSC) e do Instituto Carnegie de Washington. “Acredito que existe 100% de probabilidade de vida neste planeta, já que, apresenta as condições ideias para isso”, disse o astrónomo responsável pela investigação, Steven Vogt.”

Diário de Notícias:
“Planeta habitável a 20 anos-luz da Terra”

SIC:
“Descoberto mais um planeta “potencialmente habitável” fora do Sistema Solar
Uma equipa de astrónomos do Instituto Carnegie e da Universidade da Califórnia descobriu um novo planeta fora do nosso Sistema Solar que tem um tamanho semelhante ao da Terra e está localizado numa área que poder ser habitável. Trata-se do Gliese 581g, e está a cerca de 20 anos luz, como publicado na revista Astrophysical Journal.
Com este, há agora seis planetas que se movem, com órbitas quase circulares, em torno desta estrela (anã vermelha) e três deles são “super-Terras”, ou seja, semelhantes ao nosso, embora apenas este possa ter organismos vivos, graças à sua localização. O documento assinala ainda que, na Via Láctea possam existir muito mais planetas habitáveis do que se pensava.”

TVI:
“O planeta tem um dos lados sempre voltado para a estrela e sob influência de uma luz diária perpétua, enquanto o outro lado fica na escuridão eterna, uma vez que está voltado para o lado oposto da estrela. Consequentemente, as temperaturas decrescem do lado oposto à estrela e elevam-se do lado iluminado.
A área mais habitável do novo planeta seria a parte intermediária entre luz e escuridão. Os cientistas calculam que a temperatura média na superfície varie de 31 a 12 graus Celsius negativos.”

Eternos Aprendizes:
“Gliese 581 g: cientistas descobriram uma nova e inédita super Terra que orbita sua estrela mãe na Zona Habitável.”

Folha:
“Astrônomos americanos anunciaram ontem a descoberta de um planeta quase do tamanho da Terra que, segundo eles, teria grandes chances de ser habitável. A descoberta fica a 20 anos-luz daqui. Ou seja: em termos espaciais, ele é nosso vizinho.
O planeta recém-descoberto fica na chamada “zona habitável” – local que reúne condições para que haja água em estado líquido – de uma estrela anã conhecida como Gliese 581. Embora os cientistas ainda não tenham encontrado indícios de que realmente exista água por lá, eles já demonstram entusiasmo.
“As chances de que exista vida neste planeta é de 100%”, afirma Steven Vogt, um dos autores do trabalho, publicado na revista científica “Astrophysical Journal”. ”

Inovação Tecnológica:
“Se as observações iniciais forem confirmadas, este pode ser o exoplaneta mais parecido com a Terra já descoberto e o primeiro forte candidato para ser potencialmente habitável.
Para os astrônomos, um planeta “potencialmente habitável” é um planeta capaz de sustentar a vida, mas não necessariamente seria algo que os humanos considerariam um lugar agradável para viver.
A habitabilidade depende de muitos fatores, mas a água líquida e uma atmosfera estão entre os mais importantes.
“Nossos resultados oferecem um caso muito convincente para um planeta potencialmente habitável,” disse Steven Vogt, membro da equipe. “O fato de termos sido capazes de detectar esse planeta tão rapidamente e tão perto nos diz que planetas como este devem ser muito comuns”.”

Record:

NASA:
“NASA and NSF-Funded Research Finds First Potentially Habitable Exoplanet. (…)
“Our findings offer a very compelling case for a potentially habitable planet,” said Vogt. “The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common.”

National Geographic:
“Astronomers studying a nearby star say they’ve found the first potentially habitable planet—likely a rocky place with an atmosphere, temperate regions, and crucially, liquid water, considered vital for life as we know it.”

Universe Today:
“An enticing new extrasolar planet found using the Keck Observatory in Hawaii is just three times the mass of Earth and it orbits the parent star squarely in the middle of the star’s “Goldilocks zone,” a potential habitable region where liquid water could exist on the planet‘s surface. If confirmed, this would be the most Earth-like exoplanet yet discovered and the first strong case for a potentially habitable one. The discoverers also say this finding could mean our galaxy may be teeming with prospective habitable planets.”

Universe Today:
“Could Chance for Life on Gliese 581g Actually Be “100%”?
The announcement yesterday of the discovery of the closest Earth-sized planet found so far that also exists in the habitable zone around its star is certainly exciting (read our previous article for all the details). Gliese 581g is surely a potential habitable planet where liquid water could exist on the planet‘s surface, and many are touting the old adage of where there’s water, there’s life. However, some quotes from one of the scientists involved in the discovery might be feeding some wild speculation about the potential for life on this extrasolar planet and elsewhere. “Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say, my own personal feeling is that the chances of life on this planet are 100 percent,” said discoverer and astronomer Steven Vogt during a press briefing yesterday. “I have almost no doubt about it.”
Yes, that is an exact quote. He really used those words. He also said that it would be pretty hard to imagine that water wouldn’t exist on the planet, given the ubiquity of water in our solar system and beyond, and the habitable region in which this planet orbits.
Also participating in the briefing was Paul Butler of the Carnegie Institution of Washington, which provided funds for the observations at the Keck I telescope, and his comments were more tempered.
“Any discussion of life on at this point is purely speculative,” Butler said. “What we know is that this planet exists at the right distance for liquid water it has the right amount of mass to hold on to its atmosphere and any liquid water on the surface. So any subsequent discussion of life there is purely speculative. That being said, on the Earth anywhere you find liquid water you find life in overwhelming abundance. The question should be, if this planet has liquid water, how can you rule out life doesn’t exist? It is pretty probable that anywhere you find liquid water pooling, that you would find life existing.”
Are Vogt’s claims too extreme, or were they made in exhilaration during an exciting announcement?”

Universe Today:
“The Gliese 581 system has been making headlines recently for the most newly announced planet that may lie in the habitable zone. Hopes were somewhat dashed when we were reminded that the certainty level of its discovery was only 3 sigma (95%, whereas most astronomical discoveries are at or above the 99% confidence level before major announcements), but the Gliese 581 system may yet have more surprises.”

Astrobiology Magazine:
“A team of scientists has announced the discovery of a planet with three times the mass of Earth orbiting a nearby star at a distance that places it in the middle of the star’s “habitable zone”.
This is the first Earth-like planet found in another solar system that could have the conditions necessary for life as we know it”

Space Daily:
“(…) discovery of a planet with three times the mass of Earth orbiting a nearby star at a distance that places it squarely in the middle of the star’s “habitable zone.”
(…) The research, sponsored by NASA and the National Science
Foundation, placed the planet in an area where liquid water could exist on the planet’s surface. If confirmed, this would be the most Earth-like exoplanet yet discovered and the first strong case for a potentially habitable one.
To astronomers, a “potentially habitable” planet is one that could sustain life, not necessarily one where humans would thrive. Habitability depends on many factors, but having liquid water and an atmosphere are among the most important.”

UCSC:
“Newly discovered planet may be first truly habitable exoplanet.
Discovery suggests our galaxy may be teeming with potentially habitable planets.
“Our findings offer a very compelling case for a potentially habitable planet,” said Steven Vogt, professor of astronomy and astrophysics at UC Santa Cruz. “The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common.”

Scientific American:
“Planet Hunters Discover a World That Could Harbor Life.”

BBC:
“Astronomers have detected an Earth-like exoplanet that may have just the right kind of conditions to support life.”

New York Times:
“New Planet May Be Able to Nurture Organisms.
It might be a place that only a lichen or pond scum could love, but astronomers said Wednesday that they had found a very distant planet capable of harboring water on its surface, thus potentially making it a home for plant or animal life.
Nobody from Earth will be visiting anytime soon: The planet, which goes by the bumpy name of Gliese 581g, is orbiting a star about 20 light-years away in the constellation Libra.
But if the finding is confirmed by other astronomers, the planet, which has three to four times the mass of Earth, would be the most Earthlike planet yet discovered, and the first to meet the criteria for being potentially habitable.”

Time:
“(…) None of this proves that there is water on Gliese 581g. “Those are things we just have to speculate about,” says Vogt. But he goes on to point out that there’s water pretty much everywhere else you look. “There’s water on Earth,” he says, “and on the moon, and Mars, and on Jupiter’s moon Europa and Saturn’s moon Enceladus, and in interstellar space. There’s enough water produced in the Orion Nebula every 24 seconds to fill the Earth’s oceans.”
It’s not hard to imagine, in other words, that Gliese 581g might have plenty of water as well. “It could have quite a good ocean,” Vogt says. Certainly, it could be a sterile, nonbiological ocean. But unlike any planet found until now, there’s nothing to rule out the idea that it could be teeming with life.”

Centauri Dreams:
“Gl 581g: Rocky and Potentially Habitable.
What exactly does the word ‘habitable’ mean? The question comes to mind because of two things, the first being the media buzz over Gliese 581g, now widely described as the first potentially habitable planet we’ve found. The second is Paul Davies’ presentation yesterday at the International Astronautical Congress in Prague, where Davies was careful to differentiate between ‘habitable’ and ‘inhabited.’”

Life Unbounded:
“This is the first world that clearly ticks off two key boxes in the laundry list for habitable planets – it’s very close in mass to the Earth, and sits at a perfect distance from its parent star to stand a chance of having a temperate surface. It’s a wonderful and thrilling discovery, and I’ll confess to going out and staring in the direction of Libra last night – although sadly Gliese 581 is too faint to see directly with our beady human eyes. The relative ease (relative being the operative word, it took the might of the Keck observatory to pin this down) of finding this world and its sisters is a potent indicator that planets like this are quite common.”

Guardian:
“New Earth-like planet discovered.
Gliese 581g is in the ‘Goldilocks zone’ of its solar system, where liquid water could exist, and is a strong contender to be a habitable world.”

The Register:
“Stargazing boffins say they have discovered evidence of a potentially habitable world orbiting a star just 20 light-years from Earth. They add that the circumstances of the discovery suggest that the galaxy may be “teeming with potentially habitable planets”.”

FOXnews:
“If confirmed, the exoplanet, named Gliese 581g, would be the first Earth-like world found residing in a star’s habitable zone — a region where a planet’s temperature could sustain liquid water on its surface.”

Telegraph:
“Gliese 581g: the most Earth like planet yet discovered.
A newly discovered planet may be the most Earth like yet and so most likely to be habitable, claim scientists.”

Telegraph: um dos cientistas, diz que a vida é certa neste planeta!
“Alien life certain to exist on Earth-like planet, scientists say.
The chances of alien life existing on a newly-discovered Earth-like planet are 100 per cent, an astronomer has claimed.”

Telegraph:
“A senior professor at the University of California has come out with a rather dramatic statement. Prof Steven Vogt is “100 per cent” sure that Gliese 581g, a new planet discovered 20 light years away, is home to life.
So is this it? Have we found alien life? Are we no longer alone? Is this, in short, the biggest story of all time?
Well, potentially. Sort of. No, not really. Not yet. Prof Vogt seems to have said this in a bit of a moment of understandable excitement, because he reels it back in a bit in his very next sentence: “I would say, my own personal feeling is that the chances of life on this planet are 100 percent. I have almost no doubt about it.” (Italics mine.)
Almost no doubt is, of course, not the same as 100 per cent certainty. Prof Vogt clearly believes it is very likely that Gliese 581b is home to life, but it sounds as though, under the glare of the cameras, he may have overstated his case.”

Wikipedia: o planeta terá água líquida na sua superfície, e quiçá vida!
“Results from the study imply that the planet is located in the middle of the “Goldilocks”, or habitable zone of its parent star, where the existence of liquid water is considered a strong possibility. (…) is believed to be the first Goldilocks planet ever found, the most Earth-like planet, and the best exoplanet candidate with the potential for harboring life found to date.”

APOD:
“Earthbound telescopes had detected the signatures of multiple planets orbiting the cool sun, two at least close to the system’s habitable zone — the region where an Earth-like planet can have liquid water on its surface. Now a team headed by Steven Vogt (UCO Lick), and Paul Butler (DTM Carnagie Inst.) has announced the detection of another planet, this one squarely in the system’s habitable zone. (…) Finding a habitable planet so close by suggests there are many others in our Milky Way galaxy.”

Space.com:
“Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say, my own personal feeling is that the chances of life on this planet are 100 percent,” said Steven Vogt, a professor of astronomy and astrophysics at the University of California, Santa Cruz, during a press briefing today. “I have almost no doubt about it.”
His colleague, Paul Butler of the Carnegie Institution of Washington, in Washington, D.C., wasn’t willing to put a number on the odds of life, though he admitted he’s optimistic.
“It’s both an incremental and monumental discovery,” Sara Seager, an astrophysicist at the Massachusetts Institute of Technology, told SPACE.com. Incremental because the method used to find Gliese 581g already has found several planets most of the known planets, both super-Earths, more massive than our own world outside their stars’ habitable zone, along with non-Earth-like planets within the habitable zone.
“It really is monumental if you accept this as the first Earth-like planet ever found in the star’s habitable zone,” said Seager, who was not directly involved in the discovery.”

Space.com:
“The announcement Wednesday of two newfound alien planets circling the star Gliese 581 adds to the nearby solar system’s intrigue, further cementing its status as a top candidate to harbor extraterrestrial life.
One of the two newly discovered planets, known as Gliese 581g, is a small, Earth-like world that likely lies within its star’s habitable zone — the just-right range of distances that allow liquid water to exist.
Astronomers have now detected six planets orbiting Gliese 581, the most known to circle any star beyond our own sun. Here’s a brief tour of the star and its planets, from the inside out: (…)”

Leiam o artigo científico, aqui, e o PDF.

Vejam este vídeo da TVI.

Vejam este vídeo, em português, na Euronews.

Vejam este vídeo no jornal Folha.