The 12 planets most likely to contain life

Kepler22b artworkNASA/Ames/JPL-CaltechKepler-22b’s 290-day orbital period makes the conditions on the planet similar to those on Earth.

Scientists have discovered a rocky “mega-Earth” that expands the definition of planets beyond our solar system that could potentially host life.

The discovery of the new planet, Kepler 452b, is a new milestone in the 20-year hunt for a planets outside our solar system.

The find follows the discovery of Kepler-10c in June last year.

This amazing find comes with the tantalising question: Does this planet currently have life or did it at some point in the past?

The Planetary Habitability Laboratory run by the University of Puerto Rico at Arecibo maintains a list of exoplanets that are most similar to Earth, taking size, mass, and distance from their host stars into consideration — factors that are likely to support liquid water and would conducive to life as we know it.

The catalogue does not guarantee that these planets host life but “lists the best candidates so far for potential habitable worlds and the objects of interest for the search of life outside the Solar System.”

Here’s a look at some of the top candidates from the catalogue, ranked in order of Earth similarity.

12. Gliese-581d

Gliese-581d is one of five planets to be discovered orbiting red dwarf star Gliese 581. It is bigger than 581g, with a mass at least seven times Earth's and twice as big in size.

The planet orbits on the outer edge of the habitable zone and could be warm enough to support clouds, oceans, and rain.

11. Kepler 186f

The artist's concept depicts Kepler-186f, the first validated Earth-size planet orbiting a distant star in the habitable zone.

One of the latest additions to the catalogue is Kepler-186f, which is 450 light-years away and is the most Earth-like in size to be found in the habitable zone of its star.

The newly-found planet, described as 'Earth's cousin,' is about 10% larger than Earth and could have liquid water on its surface. That water may be frozen since it orbits the outer edge of the habitable zone. Its host star is also cooler and much smaller than our sun.

Scientists still don't know what Kepler 186f is made of, but think it could have a rocky surface like Earth. Ready to go?

10. Kepler-62f

Kepler-62f is the second potentially habitable planet found orbiting the sun-like Kepler 62, discovered April 18, 2013.

The planet is smaller than Kepler-62e at 1.41 times the radius of our planet.

Scientists think Kepler-62f could be rocky, based on observations of exoplanets that are similar in size.

9. Kepler-22b

Although Kepler-22b is 600 light-years away and about twice as big as our own planet, its 290-day orbital period makes the conditions on the planet similar to those on Earth. Its host star is in the same class our sun, but slightly smaller and cooler.

It is not clear if Kepler-22b is gaseous, rocky, or liquid, although an artist's interpretation shows clouds in its atmosphere. Kepler-22b is 2.4 times the radius of Earth

8. HD-40307 g

HD 40307 g is one of six planets to orbit around a star called HD 40307, which is 42 light-years away from Earth.

Although the planet is at least seven times the mass of Earth, scientists believe it could have an Earth-like climate because it orbits its parent star at a distance that is similar to that of Earth around our sun.

The planet is far enough away from HD 40307 that it is not tidally locked, meaning it rotates on an axis and does not always show the same face to its star, and each hemisphere has a proper daytime and nighttime.

7. Gliese-163c

In September 2012, an international team of astronomers using the European Southern Observatory's telescope in Chile, discovered Gliese-163c orbiting the star Gliese 163 about 50 light-years from Earth.

Gliese-163c is about seven times the mass of Earth and takes just 26 days to orbit its host star.

6. Gliese-581g

Gliese 581g was the first potentially habitable exoplanet discovered by astronomers in September 2010. The distant orb circles a red dwarf star called Gliese 581 that is located about 20 light-years away from Earth.

Gliese 581g, which exists in a five-planet system, is about three times as massive as our planet and is probably rocky, rather than made of gas.

The planet always shows the same face toward its host star as it whips around once every 37 days. This means it is always light in one hemisphere and constantly dark in the other, so that living along the 'light-dark' border would be the most comfortable location to set up house.

5. Tau Ceti e

Tau Ceti e is one of five planets to circle Tau Ceti, which at a distance of 12 light-years, is the closest sun-like star to Earth.

Tau Ceti e is about five times the mass of our planet.

4. Kepler-296f

Kepler-296f is roughly twice the size of Earth. It's part of a binary star system that is home to five planets.

3. Kepler-283c

Kepler-283c is one of two planets that orbits the star Kepler-283.

It's about 1.8 times larger than Earth and completes one orbit every 93 days.

2. Kepler-62e

Kepler-62e was added to the habitable exoplanet catalogue last year.

The planet is 1.61 times the radius of Earth, although astronomers do not yet know its mass or what it is made of. It could be rocky like Mars or a waterworld. Researchers should be able to discover more about the planet by studying the light that bounces off of it.

To visit our potential new home, space enthusiasts will have to travel 1,200 light-years from Earth, where the planet can be found whirling around a sun-like star called Kepler 62, which is slightly smaller and cooler than our sun.

1. Gliese-667C c

Gliese-667C c, discovered in February 2012, is about 4.5 times the mass of Earth.

The Super-Earth is found 22 light-years away, circling a red dwarf star called Gliese-66C at a distance that is closer than Mercury is to our sun.

It is still possible that Gliese-667C c could have Earth-like temperatures, however its parents star is dimmer than our own sun, which reduces the amount of radiation hitting the planet.

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