Kepler 452b (right) is about 60 per cent larger in diameter than Earth (Artist鈥檚 impression: NASA/JPL-Caltech/T. Pyle)
Meet Kepler 452b, Earth鈥檚 new alien cousin. This rocky planet is the first alien world we鈥檝e seen that circles a sun-like star at a distance that should allow liquid water to exist on its surface.
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The planet came to light after a first pass through the full data set collected during the NASA Kepler telescope鈥檚 four-year run. The analysis also yielded about a dozen other candidate worlds close to the size of Earth in the habitable zone around their stars.
Kepler鈥檚 original mission has ended, so the new discoveries come not from new data but from ever-more-thorough analyses of the existing data. Small Earth-like planets have proved the hardest to tease out. 鈥淲e鈥檙e treading through the weeds looking for these tiny stones,鈥� says from the NASA Ames Research Center in California.
The new search adds more than 500 planets to the roughly , of which about a quarter of have already been confirmed through follow-up studies.
But the newest confirmed planet, 452b, is in an Earth-like class by itself. 鈥淭oday the Earth is a little less lonely, because there鈥檚 a new kid on the block,鈥� says , also at NASA Ames. The new planet was confirmed when team members calculated that there was a less than 1 per cent chance that a pair of eclipsing binaries or a background transiting planet could be polluting the signal.
Older sibling
The planet鈥檚 star is about 1400 light years away in the constellation Cygnus. We鈥檝e previously seen a small planet in the habitable zone around a red dwarf, but 452b orbits a star just slightly bigger than our sun 鈥� meaning we understand its host star much better. Even the planet鈥檚 year is familiar at 385 days long.
That still doesn鈥檛 make Kepler 452b a perfect Earth analogue, though. It is 60 per cent larger than the Earth, and probably weighs about five times as much, which would probably drive volcanic activity.
Geological models suggest it would have a rocky composition and a thick atmosphere. And although the planet鈥檚 host star resembles the sun, it鈥檚 about 1.5 billion years older. That makes the star glow hotter, perhaps pushing 452b closer to a runaway greenhouse effect that would make it inhospitable to life.
Yet models of the star and planet still suggest that there鈥檚 been plenty of time in which water could have existed on 452b鈥檚 surface. 鈥淚t鈥檚 simply awe inspiring to consider this planet spent 6聽billion years in the habitable zone, which is longer than the age of the Earth,鈥� Jenkins says.
In addition to narrowing the search for Earth twins, the Kepler team is still working on its ultimate goal: determining the abundance of habitable, Earth-like planets in our galaxy. Specific planet discoveries demand such lavish attention because the mission will only find a few potentially habitable worlds, a small sample which has to be handled with statistical care, Batalha says. The final answer should come after another full sweep through Kepler鈥檚 data 鈥� due next year.
