Galaxy 'full of planets that could support human life'
THE Milky Way 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 could be capable of supporting life, a study has found.
Astronomers have calculated that about one in every five of the billions of Sun-like stars in our galaxy has at least one rocky planet orbiting them at a distance where water is neither frozen solid nor boiled dry.
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 number of "exoplanets" 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 100 billion and 400 billion 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.
The now-defunct Kepler space telescope, launched in 2009, was designed to detect the tiniest changes in a star's brightness as an orbiting planet crosses in front of it.
The signal had to be highly repeatable to confirm the existence of an orbiting planet.
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 – gaseous giants such as Jupiter, those with thick atmospheres such as Neptune, or hot planets that orbit much too close to their star.
"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," said Andrew Howard of the University of Hawaii.
The scientists focused on 42,000 stars that are similar in size and temperature to our own Sun. They found 603 planets orbiting these stars, but only 10 were the in the same size-range as Earth and with an orbit suitable for liquid water.
It is likely that many of the Earth-size planets are not suitable for life even though they fall in to the habitable zone. (© Independent News Service)