NASA Kepler celebrates five years in space

The panel features an image of NASA Kepler's launch and artist concepts of milestone discoveries (l to r): Kepler-9b and c, Kepler-10b, Kepler-11, Kepler-16b, Kepler-22 and Kepler-64f. 

The final panel illustrates exoplanet discoveries: blue is previous; red is previous Kepler; gold is Kepler's on Feb. 26. 

Credit: NASA Ames/W. Stenzel

Five years ago today, on March 6, 2009, NASA Kepler Space Telescope rocketed into the night skies above Cape Canaveral Air Force Station in Florida to find planets around other stars, called exoplanets, in search of potentially habitable worlds.

Since then, NASA Kepler has unveiled a whole new side of our galaxy—one that is teeming with planets. Because of Kepler we now know that most stars have planets, Earth-sized planets are common, and planets quite unlike those in our solar system exist.

By analyzing Kepler data, scientists have identified more than 3,600 candidates believed to be planets, and verified that 961 of those candidates actually are planets, many as small as Earth.

Discoveries made using Kepler now account for more than half of all the known exoplanets.

William Borucki

"During the last five years, Kepler has produced results needed to take the next big step forward in humankind's search for life in our galaxy, providing information needed for future missions that will ultimately determine the atmospheric composition of Earth-sized exoplanets to discover if they could be habitable," said William Borucki, Kepler principal investigator at NASA's Ames Research Center in Moffett Field, Calif.

Kepler's finds include planets that orbit in the habitable zone, the range of distances from a star where the surface temperature of an orbiting planet may be suitable for life-giving liquid water.

This diagram compares our own solar system to Kepler-22, a star system containing the first "habitable zone" planet discovered by NASA's Kepler mission. 

The habitable zone is the sweet spot around a star where temperatures are right for water to exist in its liquid form. 

Liquid water is essential for life on Earth.

Kepler-22's star is a bit smaller than our sun, so its habitable zone is slightly closer in. 

The diagram shows an artist's rendering of the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. Kepler-22b has a yearly orbit of 289 days. 

The planet is the smallest known to orbit in the middle of the habitable zone of a sun-like star. It's about 2.4 times the size of Earth.

Image credit: NASA/Ames/JPL-Caltech

One example of a habitable zone planet found by the mission is known as Kepler-22b.

At 2.4 times the size of Earth, it is thought to be too big to be rocky and support life.

The artist's concept depicts Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra.

Scientists believe other habitable zone planets found by the Kepler mission might be rocky, such as Kepler-62f, which is 40 percent larger in size than Earth.

A twin to Earth, a planet with the same temperature and size as Earth, has not yet been identified, but the analysis is far from over as scientists continue to search the Kepler data for the tiny signature of such a planet.

Other Kepler discoveries include hundreds of star systems hosting multiple planets, and have established a new class of planetary system where planets orbit more than one sun.

In August of last year, the mission ended its science observations after a faulty reaction wheel affected the telescope's ability to point precisely.

The mission may be able to operate in a different mode, and continue to do science.

This next-generation mission proposal, called K2, will be considered for funding by NASA in the 2014 Astrophysics Senior Review of Operating Missions.