Astronomers reveal top 20 planets with aliens, most similar to Earth

• Second Earth’ found orbiting sun’s stellar neighbour could have oceans of liquid water
• NASA’s Kepler has discovered over 4,000 exoplanets in three years
• Theory says life could have evolved on Venus with ‘nudge’ in conditions

The United States Aeronautic Space Agency (NASA’s) Kepler telescope has been busy in the hunt for alien life, finding over 4,000 new planets outside Earth’s solar system over the past three years.

Now a team of astronomers has narrowed down this list to those with the most potential to have liquid water, or even life.They pinpointed 20 out of the 4,000 that are most likely to be like our own, and are starting to look more closely at these candidates.The ‘habitable zone’ is an area around a star in which an orbiting planet’s surface could hold liquid water.

The boundaries of the habitable zone are critical. If a planet is too close to its star, it will experience a runaway greenhouse gas effect, like Venus. But if it’s too far, any water will freeze, as is seen on Mars.A group led by San Francisco State University physicists searched through the list Kepler had returned to find those most likely to support life like our own.

They found 216 Kepler planets are located within the ‘habitable zone’ – an area around a star in which an orbiting planet’s surface could hold liquid water.Of those, they list 20 that are the best candidates to be habitable rocky planets like Earth.These include Kepler-186 f, Kepler-62 f, Kepler-283 c and Kepler-296 f.

Meanwhile, if reports of a new discovery are to be believed, of all the 100 billion stars in our universe, the one closest to us might just be one that supports alien life.According to reports, a newly-spotted planet in our galactic neighbourhood might have the right conditions for life.

Scientists spotted the planet, which is believed to be ‘Earth-like’, orbiting the star Proxima Centauri, the nearest stellar neighbour to our sun.The researchers are due to unveil the discovery later this month and apparently believe it orbits its star at a distance that could favour life – the so-called habitable zone, claims German weekly Der Spiegel.

Proxima Centauri is part of the Alpha Centauri star system just 4.2 light years from our own solar system.According to Der Spiegel, the European Southern Observatory (ESO) will announce the finding at the end of August.ESO spokesman Richard Hook said he is aware of the report, but refused to confirm or deny it. “We are not making any comment,” he said.

Proxima Centauri is the closest star to our own. A planet orbiting the star would be the closest exoplanet to Earth.Discovered in 1915, Proxima Centauri is one of three stars in the Alpha Centauri system, a constellation mainly visible from the southern hemisphere.The planet is thought to be in the star’s ‘habitable zone’ – an area around a star in which an orbiting planet’s surface could hold liquid water.

Meanwhile, a new theory has claimed if conditions had been just a little different, life could exist on a lush, green Venus and Earth would be a dead planet.Researchers say that minor evolutionary changes could have altered the fates of both Earth and Venus – and hope to soon be able to model them.

This could make the search for alien life far more fruitful, and rewrite the theory of ‘goldilocks zones’ where life can exist. The hypothesis by Rice University scientists and their colleagues is published in Astrobiology this month.

The Goldilocks zone has long been defined as the band of space around a star that is not too warm, not too cold, rocky and with the right conditions for maintaining surface water and a breathable atmosphere.

But that description, which to date scientists have only been able to calibrate using observations from our own solar system, may be too limiting, Rice Earth scientist Adrian Lenardic said.Lenardic and his colleagues suggested that habitable planets may lie outside the ‘Goldilocks zone’ in extra-solar systems, and that planets farther from or closer to their suns than Earth may harbor the conditions necessary for life.

“For a long time we’ve been living, effectively, in one experiment, our solar system,” he said.Lead author of the first study, Prof. Stephen Kane, said: “This is the complete catalogue of all of the Kepler discoveries that are in the habitable zone of their host stars.

“That means we can focus in on the planets in this paper and perform follow-up studies to learn more about them, including if they are indeed habitable.“This study is a really big milestone toward answering the key questions of how common is life in the universe and how common are planets like the Earth.”

The research also confirms the distribution of Kepler planets within the habitable zone is the same as the distribution of those outside of it.This means the universe is teeming with planets and moons where life could potentially exist.

The researchers further sorted them by planet size: smaller, rocky planets versus larger gas giants.The 20 planets in the most restrictive category, rocky surface and a conservative habitable zone, are the most likely to be similar to Earth.

Kane has already started to gather more data on these planets, as well as those in the other categories.“It’s exciting to see the sheer amount of planets that are out there, which makes you think that there is zero chance of there not being another place where life could be found,” said Michelle Hill, undergraduate student.The four categories are aimed at helping astronomers focus their research.

Those looking for moons that could potentially hold life can study exoplanets in the gas giant categories, for example.“There are a lot of planetary candidates out there, and there is a limited amount of telescope time in which we can study them,” Kane said.

“This study is a really big milestone toward answering the key questions of how common is life in the universe and how common are planets like the Earth.”An international team of astronomers has discovered a treasure trove of new worlds.Both Kepler and its K2 mission discover new planets by measuring the subtle dip in a star’s brightness caused by a planet passing in front of its star.

As early as 2012, Kepler scientists found that all five planets orbit in an area about 150 times smaller than the Earth’s orbit around the Sun, with ‘years’ of about one, three, four, seven and nine days.So far they have reported finding 197 planet candidates, with 104 planets confirmed by scientists.The planets, which are all between 20 and 50 per cent larger than Earth by diameter, are orbiting the M dwarf star K2-72, found 181 light years away.

The scientists, led by the University of Arizona, said the possibility of life on the new planets around such a star could not be ruled out.Four of the planets discovered have been found to be rocky, and could host alien life. They are thought to be between 20 and 50 per cent more massive than Earth, and they orbit a star smaller than our sun.

Two of the worlds could have radiation levels that are similar to Earth. The huge finding of planets was found by combining data with follow-up observations by earth-based telescopes including the North Gemini telescope and the WM Keck Observatory in Hawaii.

A crop of more than 100 planets, discovered by NASA’s Kepler Space Telescope, includes four in Earths 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 stars ‘habitable’ zone, where liquid water could exist on the surface. These small, rocky worlds are far closer to their star than Mercury is to our sun.