Kepler gets mission extension in its search for Earth-like worlds

Timeline depicting major milestones during the Kepler mission so far.
Credit: NASA Ames Research Center / W. Stenzel

To say that the Kepler mission has been successful so far would be a major understatement – with 2,321 exoplanet candidates and 105 confirmed exoplanets to date, Kepler has revolutioned our understanding of planetary systems around other stars. Not all that long ago it wasn’t even known if any planets existed outside our solar system, and now they are being discovered on a regular basis.

But there’s other good news too. The Kepler mission has been extended, which is necessary for it to be able to find even more planets, specifically ones that are about the size of Earth, orbiting in their stars’ habitable zones.

Kepler just completed its primary 3 1/2 year mission and has already discovered an amazing variety of worlds, including “hot Jupiters” and “super-Earths” as well as planets in systems with two or even four suns!

“The initial discoveries of the Kepler mission indicate that at least a third of the stars have planets and that the number of planets in our galaxy must number in the billions,” said William Borucki, Kepler principal investigator at NASA’s Ames Research Center.

The primary focus and goal of Kepler, however, is to find other planets that are similar to Earth – rocky worlds about the same size and not too close their stars, allowing liquid water to exist on their surfaces. They are among the most difficult to detect; because it can take a few years to repeatedly observe a planet’s orbit around its star; the easiest ones to find first are those that are closer in, in smaller orbits (or larger gas giants like Jupiter) and Kepler has been finding those in large numbers.

“The planets of greatest interest are other Earths and these could already be in the data awaiting analysis. Kepler’s most exciting results are yet to come!,” Borucki adds.

To find smaller planets like Earth in larger orbits requires longer observing time. Kepler’s mission extension will provide that much-needed extra time, enabling it to confirm planets in orbits similar to Earth’s and in a star’s habitable zone (the habitable zone can also vary depending on the star’s size and luminosity). In our solar system, it extends roughly from the orbit of Venus to just past the orbit of Mars.

As Geoff Marcy, professor of astronomy at the University of California, Berkeley, so eloquently puts it, “The Earth isn’t unique, nor the center of the universe. The diversity of other worlds is greater than depicted in all the science fiction novels and movies. Aristotle would be proud of us for answering some of the most profound philosophical questions about our place in the universe.”

This article was first published on

Paul Scott Anderson is a freelance space writer with a life-long passion for space exploration and astronomy. He started his blog The Meridiani Journal in 2005, which is a chronicle of planetary exploration. He also publishes The Exoplanet Report e-paper. In 2011, he started writing about space on a freelance basis, and now also currently write for AmericaSpace and He has also written for Universe Today and SpaceFlight Insider, has been published in The Mars Quarterly and has done supplementary writing for the well-known iOS app Exoplanet for iPhone and iPad.