Is the Earth is the only planet in the universe where life exists? I think it’s impossible. Until recently it was thought that our solar system is the only planetary system. Now it turns out that the planets are quite common.

So let’s look at the five planets, which has the potential to develop life. All images in this article are artistic visions of the planets.

Gliese 581g


Gliese 581 g (pron.: /ˈɡliːzə/), also Gl 581 g or GJ 581 g, is an unconfirmed extrasolar planet claimed to orbit the red dwarf star Gliese 581, 22 light-years from Earth in the constellation of Libra. It is the sixth planet purportedly discovered in the Gliese 581 planetary system and the fourth in order of increasing distance from the star. The discovery was announced by the Lick-Carnegie Exoplanet Survey in late September 2010, after a decade of observation. However, the ESO/HARPS survey team was not able to confirm that the planet exists.

Gliese 581 g has attracted attention because it is near the middle of the habitable zone of its parent star. That means it could sustain liquid water on its surface and could potentially host life similar to that on Earth. The planet is expected to have temperatures around −37 to −12 °C, however. If it is a rocky planet, favorable atmospheric conditions could permit the presence of liquid water, a necessity for all known life, on its surface. With a mass 3.1 to 4.3 times Earth’s, Gliese 581 g is considered a super-Earth and is the planet closest in size to Earth known in a habitable zone. This makes it the most Earth-like Goldilocks planet found outside the Solar System and the exoplanet with the greatest recognized potential for harboring life.
The supposed detection of Gliese 581 g after such a short period of searching and at such close proximity has led some astronomers to hypothesize that the proportion of stars with habitable planets may be greater than ten percent.

The planet is tidally locked to the star, meaning that one side is always facing the star and basking in perpetual daylight, while the side facing away from the star is in perpetual darkness. One effect of this is to stabilize the planet’s surface climates, according to Vogt. The most habitable zone on the planet’s surface would be the line between shadow and light (known as the “terminator”).

Gliese 667C c


This artist’s impression shows a sunset seen from the super-Earth Gliese 667 Cc. The brightest star in the sky is the red dwarf Gliese 667 C, which is part of a triple star system. The other two more distant stars, Gliese 667 A and B appear in the sky also to the right. Astronomers have estimated that there are tens of billions of such rocky worlds orbiting faint red dwarf stars in the Milky Way alone. Caption and image courtesy of the ESO/L. Calçada

Gliese 667 C is a member of a triple star system in the constellation Scorpius, 22.1 lightyears from the Earth . According to a study by Delfosse and collaborators from the Joseph Fourier University in Grenoble the planet Gliese 667 Cc is right in the middle of the habitable zone. It receives only 10 percent less stellar energy than the Earth receives from the Sun.

It is said to be within the habitable zone – an area far enough away from the sun where it isn’t too hot or too cold. Otherwise known as the “Goldilocks” zone, the area is a pretty good breeding ground for microbial life as liquid water could exist.

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“It´s the Holy Grail of exoplanet research to find a planet orbiting around a star at the right distance so it´s not too close where it would lose all its water and not too far where it would freeze,” Steven Vogt, an astronomer from the University of California, said in this article. “It´s right there in the habitable zone – there´s no question or discussion about it. It is not on the edge. It is right in there.”

Kepler-22b


The newly confirmed planet, Kepler-22b, is the smallest yet found to orbit in the middle of the habitable zone of a star similar to our sun. The planet is about 2.4 times the radius of Earth. Scientists don’t yet know if Kepler-22b has a predominantly rocky, gaseous or liquid composition, but its discovery is a step closer to finding Earth-like planets.

“Fortune smiled upon us with the detection of this planet,” said William Borucki, Kepler principal investigator at NASA Ames Research Center at Moffett Field, Calif., who led the team that discovered Kepler-22b. “The first transit was captured just three days after we declared the spacecraft operationally ready. We witnessed the defining third transit over the 2010 holiday season.”

Kepler-22b is located 600 light-years away. While the planet is larger than Earth, its orbit of 290 days around a sun-like star resembles that of our world. The planet’s host star belongs to the same class as our sun, called G-type, although it is slightly smaller and cooler.

This diagram compares our own solar system to Kepler-22, a star system containing the first “habitable zone” planet discovered by NASA’s Kepler mission. The habitable zone is the sweet spot around a star where temperatures are right for water to exist in its liquid form. Liquid water is essential for life on Earth.Kepler-22’s star is a bit smaller than our sun, so its habitable zone is slightly closer in. The diagram shows an artist’s rendering of the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. Kepler-22b has a yearly orbit of 289 days. The planet is the smallest known to orbit in the middle of the habitable zone of a sun-like star. It’s about 2.4 times the size of Earth.
Image credit: NASA/Ames/JPL-Caltech

HD 85512 b


HD 85512 b is an extrasolar planet orbiting Gliese 370 (a K-type or “orange dwarf”) star approximately 36 light-years distance from Earth in the constellation of Vela (the Sail).
Due to its mass of at least 3.6 times the mass of Earth, HD 85512 b is classified as a super-Earth and is one of the smallest exoplanets discovered to be on the edge of the habitable zone. HD 85512 b, along with Gliese 581 d is considered to be one of the best candidates for habitability as of August 30, 2011.
Earth is considered the Goldilocks planet for its perfect combination of planet resources and its place within the habitable zone of the sun’s orbit. Meaning, it’s in the “narrow area around a star where water can exist in liquid form.” HD 85512 b also orbits within the habitable zone of its star, indicating the possibility for water if the planet is rocky and has more than 50 percent cloud cover.

In this zone it’s not too cold and not too warm, this way water won’t freeze or evaporate. Liquid water is seen as a basic essential for a planet to contain life. On HD 85512 b it is between thirty and fifty degrees. This fact, plus the high humidity would make being on this planet “like living in a hot steam bath” says researcher Lisa Kaltenegger. Furthermore the researchers think sixty percent of the planet is covered in clouds, that’s ten percent more then our earth has.

Never before has a planet been found that is so much like ours. On HD 85512 b, people could be walking around without falling through the ground, freezing, burning or choking in the atmosphere. Furthermore, it’s the biggest clue until now that we are not alone in the universe. According to research it’s not impossible that life is present on this planet. Due to the gravity being fifty percent higher then on earth creatures will be shorter, more angular and living lower to the ground.

Gliese 581d


Gliese 581d orbits a red dwarf star called Gliese 581, located around 20 light years from Earth, which makes it one of our closest neighbors. Gliese 581d orbits on the outer fringes of the star’s “Goldilocks zone”, where it is not so hot that water boils away, nor so cold that water is perpetually frozen. Instead, the temperature is just right for water to exist in liquid form.

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“With a dense carbon dioxide atmosphere — a likely scenario on such a large planet — the climate of Gliese 581d is not only stable against collapse but warm enough to have oceans, clouds and rainfall,” France’s National Center for Scientific Research (CNRS) said in a press release.

A radio message has been sent to Gliese 581 in 2008 and will reach the star system in 2029.

The habitable zone of Gliese 581 compared with our Solar System’s habitable zone. Within the zone you could see two exoplanets Gliese 581 g an Gliese 581d

Sources:
wikipedia, NASA, Space oddities