Kepler find adds to planet- hunt tally
Inching ahead on their quest for what they call Earth 2.0, NASA astronomers announced Thursday that the Kepler planet- hunting spacecraft had found what stands to be one of the closest analogs to Earth yet.
It is a planet a little more than 11/ times as big in radius
2 as Earth. Known as Kepler 452b, it circles a sunlike star in an orbit that takes 385 days, just slightly longer than an Earth year, putting it firmly in the “Goldilocks” habitable zone where the temperatures are lukewarm and suitable for liquid water on the surface — if it has a surface.
The new planet’s size is right on the hairy edge between being rocky like Earth and being a fluffy gas ball like Neptune, according to studies of other such exoplanets.
In an email, Jon Jenkins, an astronomer at NASA’s Ames Research Center, home of the Kepler project, and lead author of a paper being published in The Astronomical Journal, said the planet had between a 50 percent chance and a 62 percent chance of being rocky, depending on uncertainties in the size of its home star. That would mean its mass is about five times that of Earth.
To determine whether Kepler 452b deserves a place on the honor roll of possible habitable worlds, astronomers have to measure its mass, which requires being close enough to observe the wobbling of the star as it is tugged around by the planet’s gravity. For now that is impossible, because Kepler 452b is 1,400 light- years away.
The planet is the first to be confirmed in a new list of candidates unveiled by Kepler astronomers at a news conference Thursday. It takes the list of possible planets discovered by Kepler to 4,675.
The spacecraft, launched in 2009, spent four years staring at a patch of the Milky Way on the border between the constellations Cygnus and Lyra, looking for dips in starlight caused by planets passing in front of their stars. Its pointing system failed in 2013, but astronomers are still analyzing the data Kepler collected. Every time they sift through the data, new planets pop out.
In the meantime, Kepler has switched to a different mode of observing in a new mission astronomers call K2.
The NASA news conference coincided with a major anniversary: It was 20 years ago this fall that Michel Mayor and Didier Queloz, of the University of Geneva, discovered a planet circling the star 51 Pegasi, about 50 light- years from here.
It was the first planet known to belong to a sunlike star outside the solar system, and its discovery ignited an astronomical revolution that is still growing.
Astronomers say they now know from Kepler that about 10 percent of the 200 billion stars in the Milky Way have potentially habitable Earthsize planets, Kepler 452b probably among them.
This means that of the 600 stars within 30 light- years of Earth, there are roughly 60 potentially habitable planets, which could be inspected by a future generation of telescopes.