‘We’re Not Alone’: Milky Way Teeming with Billions of Earth-Size Planets

According to the recent NASA study there are at least 8.8 billion stars with Earth-size planets in the habitable temperature zone.

From some 150,000 stars photographed over four years, astronomers have discovered more than 3,000 planet candidates. Photo: tida_ketchup/ Flickr

A recent research shows that the Milky Way galaxy is teeming with Earth-like planets that are not too hot and not too cold for liquid water to exist at their surface – and so be capable of supporting life. The study was published Monday in the journal Proceedings of the National Academy of Science.

Scientists believe that one in five stars similar to the Sun is circled by an Earth-like planet that might be habitable. Astronomers using NASA data have calculated for the first time that in our galaxy alone, there are at least 8.8 billion stars with Earth-size planets in the habitable temperature zone. For perspective, that’s more Earth-like planets than there are people on Earth.

If people on Earth could only travel in deep space, “you’d probably see a lot of traffic jams,” Bill Borucki, NASA’s chief Kepler scientist, joked Monday.

Knowing how many rocky planets are in the so-called Goldilocks zone – neither too hot, nor too cold – was one of the central goals of the Kepler satellite mission to estimate the total number of “exoplanets” existing beyond the Solar System. The latest estimate, based on Kepler data, is the most accurate assessment so far of the number of potentially habitable planets in our own galaxy of between 100bn and 400bn stars.

“What this means is, when you look up at the thousands of stars in the night sky, the nearest Sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away and can be seen with the naked eye. That is amazing,” said Erik Petigura of the University of California, Berkeley, who led the research.

Dr. Andrew Howard, from the Institute of Astronomy at the University of Hawaii, who co-led the US study, said: “It’s been nearly 20 years since the discovery of the first extrasolar planet around a normal star.

“Since then we have learned that most stars have planets of some size and that Earth-size planets are relatively common in close-in orbits that are too hot for life. With this result we’ve come home, in a sense, by showing that planets like our Earth are relatively common throughout the Milky Way galaxy.

“For Nasa, this number – that every fifth star has a planet somewhat like Earth – is really important, because successor missions to Kepler will try to take an actual picture of a planet, and the size of the telescope they have to build depends on how close the nearest Earth-size planets are. An abundance of planets orbiting nearby stars simplifies such follow-up missions.”

The Kepler scientists reported about 3,000 planetary “candidates”, estimated by taking photographs every 30 minutes of about 150,000 stars. Many of these planets are much larger than Earth and unsuitable for water and life, such as gaseous giants like Jupiter or those with thick atmospheres like Neptune, or hot planets that orbit much too close to their star.

The next step, scientists say, is to look for atmospheres on these planets with powerful space telescopes that have yet to be launched. That would yield further clues to whether any of these planets do, in fact, harbor life, says the Huff Post.

It is likely that many of the Earth-size planets in the analysis are still not suitable for life even though they fall in to the habitable zone. Mars and Venus, for instance, are not presently habitable, although liquid water may have existed on them in the past.

The findings also raise a blaring question, study co-author Geoff Marcy said: If we aren’t alone, why is “there a deafening silence in our Milky Way galaxy from advanced civilizations?”

Kepler has identified only 10 planets that are about Earth’s size circling sun-like stars and are in the habitable zone, including one called Kepler 69-c.

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