But now Kepler is passing the torch.
Unfortunately the last five years of Kepler's exploits were hindered by malfunctioning reaction wheels, limiting the number of target stars that the space telescope could be directed towards.
Kepler made incredible discoveries, revealing that there are more planets than stars in our galaxy.
Kepler's retirement marks just the beginning of a quest to end humankind's cosmic loneliness.
Kepler is now orbiting the sun at a distance of about 94 million miles from Earth.
The $700 million mission even helped to uncover past year a solar system with eight planets, just like ours. Plus, NASA's newest planet hunter, the Transiting Exoplanet Survey Satellite, launched in April and has already identified two potential life-sustaining planets.
NASA's venerable Kepler space telescope, which discovered almost 2,700 exoplanets in distant star systems, has officially been retired after finally running out of fuel, the space agency wrote in a statement on Tuesday.
Many of these planets, he said, may be just warm enough that they could have liquid water on their surface, "a situation conducive to the existence of life".
Its scientific legacy now brought to a close, Kepler has proved that space is filled with planets more so than stars. Fuel exhaustion was seen in late June.More news: Video shows woman attacking bus driver after missing stop, causing deadly crash
When we started conceiving this mission 35 years ago, we didn't know of a single planet outside our solar system.
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.
In the course of its decade, Kepler discovered some 5,580 possible planets by staring intently at the stars in a tiny patch of the Milky Way. No, and in fact the opposite is true.
Both use the same system of detecting planetary transits, or shadows cast as they pass in front of their star. Finding so many edge-on system among Kepler's original 150,000 stars likely means that our galaxy - which has more than 100 billion stars - is likely have hundreds of billions of planets.
"The Kepler mission has paved the way for future exoplanet studying missions". It was an extremely clever approach to doing this kind of science.
However, it extended well beyond its four-year mission and survived nine eventful years in the space. But the mission team managed to salvage the telescope after figuring out how to use the pressure of sunlight to balance the spacecraft.
The observation of so many stars has allowed scientists to better understand stellar behaviors and properties, which is critical information in studying the planets that orbit them. "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". Now there is a great deal and it is clear that planets are very common. It ran out of fuel while observing a nearby star known to host seven.
The positioning system of the Kepler telescope had broken down in the year 2013, and luckily the researchers discovered a way to restore the spacecraft and got it back in operations soon. The mission was called K2 and found 350 exoplanets more than the ones uncovered since it was launched in 2009.