The Kepler space telescope of NASA which discovered 2,700 exoplanets distant star systems is now officially retired after running out of fuel.
The space agency says it has chose to retire Kepler while it is located in its present orbit, which it describes as safe and away from Earth.
As Dr Andrew Rushby, a former scientist at NASA's Ames Research Centre told ten daily earlier this year, one of Kepler's greatest contributions was the concept there are more planets than stars in our galaxy.
Kepler showed us that "we live in a galaxy that's teeming with planets, and we're ready to take the next step to explore those planets", she said.
The most recent analysis of Kepler data suggests that as many as 50 percent of visible stars have small, possibly rocky planets located within their habitable zone.
Despite a malfunctioning steering system and dwindling hydrazine fuel levels, the $600 million spacecraft stayed in action for nine years and 19 observation campaigns-far longer than its original four-year mission. Borucki sought to develop what ultimately became Kepler for decades, eventually convincing NASA that a space telescope that could perform precise photometry of thousands of stars, needed to detect the brightness variations caused by transits, was feasible.
Kepler has studied more than 500,000 stars in this way.
"That means they're located at distances from their parent stars where liquid water -- a vital ingredient to life as we know it -- might pool on the planet surface".
Thanks to the spacecraft, scientists have learned that the Milky Way galaxy has more planets than stars.
Fuel supplies of Kepler ran out two weeks ago leaving the telescope unable to function. Scientists said that Kepler's data will support further research for a decade to come.
NASA's newest planet hunter, the Transiting Exoplanet Survey Satellite, launched in April.
Nasa's retired principal investigator for the Kepler mission, Bill Borucki, described it as an "enormous success". It began science operations in late July, as Kepler was waning, and is looking for planets orbiting 200,000 of the brightest nearby stars to Earth. TESS is created to survey about 200,000 stars across a wide stretch of sky in our celestial neighborhood, and identify prospects for further study. The first data from TESS is already being sent to Earth and analyzed.
"We saw it drop from 90 psi [pounds per square inch] all the way down to 25 psi" over a few hours, said Charlie Sobeck, project system engineer for Kepler at NASA's Ames Research Center. However, although these planets tend to be the most enticing, according to Kepler, they are not the most common type of planet out there.
In 2013, mechanical errors made Kepler too unstable to continue its precision surveys.
It's the pioneering telescope which, for those of us on Earth, filled the galaxy with planets.. "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". Kepler has revolutionised our understanding of the universe.
"I think we were all extremely impressed with what it was doing for us", Borucki said of Kepler.
Planetary exploration is going through a wider-ranging changing of the guard: For example, NASA's Dawn mission to the dwarf planet Ceres is ending, due to the same empty-tank issue that Kepler faced.