NASA announced on Tuesday that the Kepler mission - which has transformed how we understand planets outside of our solar system - is officially over.
Earlier this year, it became clear that the Kepler Space Telescope was running low on fuel - NASA has since been planning a replacement to take over the iconic satellite's ongoing search for exoplanets. Its ability to point at distant stars and identify possible alien worlds worsened dramatically at the beginning of October, but flight controllers still managed to retrieve its latest observations.
The telescope has now gone silent.
Based on the planets discovered by Kepler, researchers now think about 20 to 50 percent of stars in the Milky Way harbor rocky, roughly Earth-sized planets that may be able to support liquid water on their surfaces.
For years, Kepler stared at a fixed area of the sky bridging the constellations Lyra and Cygnus to monitor about 150,000 stars for signs of planets.
Launched in March 2009, the $600 million Kepler mission searched the night sky for Earth-like planets using what's called the "transit method".More news: Kylie Jenner Surprises Kris Jenner With A Ferrari For Her 63rd Birthday
When it comes to the planet quest, the next big thing on the horizon is the James Webb Space Telescope, which is now due for launch in 2021 and may be able to look for signs of life in the atmospheres of alien planets.
Kepler's mission was to determine if earth-like planets are common or rare outside our own solar system and was originally meant to only last three-and-a-half years.
It's the pioneering telescope which, for those of us on Earth, filled the galaxy with planets..
Nasa said it has made a decision to retire the spacecraft "within its current, safe orbit, away from Earth".
But the telescope has now run out of the fuel needed for further operations.
"We know the spacecraft's retirement isn't the end of Kepler's discoveries", Kepler's project scientist Jessie Dotson said. "Now we know there are billions of planets that are rocky like the Earth and are orbiting their stars in the habitable zone, or the Goldilocks zone, where their temperatures might be conducive to water on the surface".More news: The stern demand Prince Harry issued staff three days before marrying Meghan
In all, close to 4,000 exoplanets have been confirmed over the past two decades, two-thirds of them thanks to Kepler.
"It has revolutionized our understanding of our place in the cosmos", Hertz said. In that time, it has spotted thousands of exoplanet candidates and shown us that planets are rather ubiquitous, outnumbering stars in our galaxy.
Such data has allowed scientists to better interpret stellar behavior and properties-critical to the study of stars and the planets that orbit them.
Nasa's retired principal investigator for the Kepler mission, Bill Borucki, described it as an "enormous success". It has already identified two potential planets.
"The science and new discoveries were fantastic and changed our view in many fields of astrophysics and planetary science, including, of course, exoplanets", Kepler scientist Steve Howell said via email.
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.More news: Japan launches rocket carrying greenhouse gas observation satellite
The final commands have been sent, and the spacecraft will remain a safe distance from Earth to avoid colliding with our planet. And recent glitches with the 28-year-old Hubble Space Telescope and the 19-year-old Chandra X-Ray Observatory have signaled that those grand-scale telescopes are past their prime, mechanically if not scientifically.