8 cool “habitable” planets

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With the discovery of a possibly habitable Earth-sized orbiting around our own nearest star some four light-years in the distance, we thought we’d take a look at some of the other potential Goldilocks planets discovered over the past years. Have a look…

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The newest possibility

What we see here, according to NASA, is an artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star – 4 light years -- to our solar system. Proxima b, spotted recently by a team of astronomers using the European Southern Observatory's 3.6-meter telescope at La Silla, Chile, is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface, NASA said.  While the newly discovered planet lies within its star's "habitable zone" scientists do not yet know if the planet has an atmosphere. It also orbits a red-dwarf star, far smaller and cooler than our sun. The planet likely presents only one face to its star, as the moon does to Earth. And Proxima b could be subject to potentially life-extinguishing stellar flares, NASA stated.

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Small and hot

In July, a crop of more than 100 planets was uncovered by NASA’s Kepler Space Telescope.  The group includes four in Earth’s size-range orbiting a single dwarf star. Two of these planets are too hot to support life as we know it, but two are in the star’s “habitable” zone, where liquid water could exist on the surface, NASA said. These small, rocky worlds are far closer to their star than Mercury is to our sun. But because the star is smaller and cooler than ours, its habitable zone is much closer. One of the two planets in the habitable zone, K2-72c, has a “year” about 15 Earth-days long—the time it takes to complete one orbit. This closer planet is likely about 10% warmer than Earth. On the second, K2-72e, a year lasts 24 Earth days, this slightly more distant planet would be about 6% colder than Earth, NASA said.

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Meet rocky

NASA's Kepler mission this year confirmed the first near-Earth-size planet in the “habitable zone” around a sun-like star.  The newly discovered Kepler-452b is the smallest planet to date discovered orbiting in the habitable zone -- the area around a star where liquid water could pool on the surface of an orbiting planet NASA said. Kepler-452b is 60% larger in diameter than Earth and is considered a super-Earth-size planet. While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a good chance of being rocky.  This artist's concept compares Earth (left) to the new planet, Kepler-452b.

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An artist's depiction of Kepler-62e. The super Earth-size planet is in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra.

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One of the first possibly habitable planets discovered by NASA’s Kepler was dubbed Kepler-22. Kepler-22b is about 2.4 times the radius of Earth and an orbit of 290 days around a sun-like star resembles that of our world. The planet is orbiting the same class of star as our sun, called G-type, although it is slightly smaller and cooler, NASA stated.

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Big Earth

Kepler-69c, is 70% larger than the size of Earth, and orbits in the habitable zone of a star similar to our sun. Astronomers are uncertain about the composition of Kepler-69c, but its orbit of 242 days around a sun-like star resembles that of our neighboring planet Venus, according tor NASA. The artist's concept depicts Kepler-69c, a super-Earth-size planet in the habitable zone of a star like our sun, located about 2,700 light-years from Earth in the constellation Cygnus.

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Potential life

The artist's concept depicts Kepler-186f, a validated Earth-size planet to orbit a distant star in the habitable zone—a range of distance from a star where liquid water might pool on the planet's surface. The size of Kepler-186f is known to be less than ten percent larger than Earth, but its mass, composition and density are not known. Previous research suggests that a planet the size of Kepler-186f is likely to be rocky. Prior to this discovery, the "record holder" for the most "Earth-like" planet went to Kepler-62f, which is 40% larger than the size of Earth and orbits in its star's habitable zone, according to NASA.

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Harvard-Smithsonian Center for Astrophysics

Cooler than the Sun

Kepler-438b and Kepler-442b were spotted in 2015 and both orbit red dwarf stars that are smaller and cooler than our Sun. Kepler-438b circles its star every 35 days, while Kepler-442b completes one orbit every 112 days. Kepler-438b receives about 40% more light than Earth. As a result, the Harvard-Smithsonian Center for Astrophysics  team that wrote a paper on these planets,  calculates it has a 70% likelihood of being in the habitable zone of its star.