NASA will retire the Kepler space telescope after it has run out of the fuel needed for further space operations.

During the past nine years, the Kepler telescope found more than 2,600 planets outside the Solar System, many of which could be promising for life. NASA said it will retire the spacecraft within its current, safe orbit, away from Earth.

"As NASA's first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond," said Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate in Washington. "Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars."

Through Kepler, NASA learned about the diversity of planets that exist in the Milky Way galaxy, concluding that 20 to 50% of the stars visible in the night sky are likely to have small, rocky planets similar in size to Earth and perhaps even located a habitable zone of their parent stars. A habitable zone is located at distances from a parent star where liquid water might pool on a planet’s surface.

The most common size of planet that Kepler found doesn’t exist in our solar system — a world somewhere between Earth and Neptune in size. Kepler also found that in some cases many planets orbit extremely close to stars, which is different from the well-spaced planets in our own solar system, NASA said.

Kepler’s History

Kepler found that the most common planet in the galaxy is not one in our solar system. Source: NASAWhen Kepler was launched in March of 2009, it featured the largest digital camera for outer space observations. Kepler was originally positioned to gaze continuously at 150,000 stars in one patch of the sky in the constellation Cygnus.

Five years after launch, Kepler had met its primary mission objectives but was temporarily halted due to mechanical failures. After a quick fix, the number of observed stars was bumped up to more than 500,000.

Kepler data allowed scientists to garner new research into the history of the Milky Way galaxy and the beginning stages of exploding stars called supernovae. Scientists expect to spend a decade or more in search of new discoveries near Kepler's observation area, NASA said.

"We know the spacecraft's retirement isn't the end of Kepler's discoveries," said Jessie Dotson, Kepler's project scientist at NASA's Ames Research Center in California's Silicon Valley. "I'm excited about the diverse discoveries that are yet to come from our data and how future missions will build upon Kepler's results."

When NASA discovered Kepler was in danger of having low fuel, scientists had the telescope initiate multiple observation campaigns that will complement the data from NASA’s newest planet-hunter, the Transiting Exoplanet Survey Satellite (TESS). That spacecraft was launched in April and will search planets orbiting some 200,000 of the brightest and nearest stars to the Earth and that later can be explored for signs of life by missions such as NASA’s James Webb Space Telescope.