One of the key factors in their results was Rayleigh scattering, the phenomenon that makes the sky blue on Earth. In the Solar System, Rayleigh scattering limits the amount of sunlight a thick atmosphere can absorb, because a large portion of the scattered blue light is immediately reflected back to space. However, as the starlight from Gliese is red, it is almost unaffected.
This means that it can penetrate much deeper into the atmosphere, where it heats the planet effectively due to the greenhouse effect of the CO2 atmosphere, combined with that of the carbon dioxide ice clouds predicted to form at high altitudes.
Furthermore, the 3D circulation simulations showed that the daylight heating was efficiently redistributed across the planet by the atmosphere, preventing atmospheric collapse on the night side or at the poles. Scientists are particularly excited by the fact that at 20 light years from Earth, Gliese d is one of our closest galactic neighbours.
For now, this is of limited use for budding interstellar colonists - the furthest-travelled man-made spacecraft, Voyager 1, would still take over , years to arrive there.
However, it does mean that in the future telescopes will be able to detect the planet's atmosphere directly. While Gliese d may be habitable there are other possibilities; it could have kept some atmospheric hydrogen, like Uranus and Neptune, or the fierce wind from its star during its infancy could even have torn its atmosphere away entirely.
To distinguish between these different scenarios, Wordsworth and co-workers came up with several simple tests that observers will be able to perform in future with a sufficiently powerful telescope.
If Gliese d does turn out to be habitable, it would still be a pretty strange place to visit - the denser air and thick clouds would keep the surface in a perpetual murky red twilight, and its large mass means that surface gravity would be around double that on Earth. But the diversity of planetary climates in the galaxy is likely to be far wider than the few examples we are used to from the Solar System. In the long run, the most important implication of these results may be the idea that life-supporting planets do not in fact need to be particularly like the Earth at all.
References: " Gliese d is the first discovered terrestrial-mass exoplanet in the habitable zone". Wordsworth, F. This artist concept illustrates how a massive collision of objects, perhaps as large as the planet Pluto, smashed together to create the dust ring around the nearby star Vega. New observations from Massive Smash-Up at Vega. In the three and a half years of its primary mission, NASA's Kepler spacecraft produced a mountain of data. Astronomers continue to mine it, finding new likely planets all the time - including Kepl This image shows our own back yard, astronomically speaking, from a vantage point about 30 light-years away from the sun.
It highlights the population of tiny brown dwarfs recently discovered by NA Highlighting our Tiniest Neighbors. This chart shows most of the stars visible with the unaided eye on a clear night. The star Alpha Centauri is one of the brightest stars in the southern sky marked with a red circle.
It lies just Alpha Centauri in the constellation of Centaurus The Centaur. A truly doomed planet, WASPb is being cannibalized by its star. It's a Star-Eat-Planet World. Cluster of Stars in Kepler's Sight - This image zooms into a small portion of Kepler's full field of view -- an expansive, square-degree patch of sky in our Milky Way galaxy.
This diagram compares the planets of our inner solar system to Kepler, a five-planet star system about light-years from Earth in the constellation Cygnus. The five planets of Kepler orb Kepler and the Solar System. This artist's conception illustrates a storm of comets around a star near our own, called Eta Corvi.
It's Raining Comets. Astronomers performing a new atmospheric-modeling study have found that the planet likely lies in the "habitable zone" of its host star — that just-right range of distances that allow liquid water to exist. The alien world could be Earth-like in key ways, harboring oceans, clouds and rainfall, according to the research. This conclusion is consistent with several other recent modeling studies. But it does not definitively establish that life-sustaining water flows across the planet's surface.
The new study assumes that Gliese d, which is about seven times as massive as Earth, has a thick, carbon-dioxide-based atmosphere. That's very possible on a planet so large, researchers said, but it's not a given. Gliese d's parent star, known as Gliese , is a red dwarf located 20 light-years from Earth, just a stone's throw in the cosmic scheme of things. So far, astronomers have detected six planets orbiting the star , and Gliese d is not the only one intriguing to scientists thinking about the possibility of life beyond Earth.
Another planet in the system, called Gliese g , is about three times as massive as Earth, and it's also most likely a rocky world.
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