NASA’s Kepler Space Telescope, the spacecraft known for thousands of exoplanetary discoveries, has been put on hibernation mode, again.

The telescope, which has scoured several patches of the sky for nearly a decade, is running low on fuel and the agency has decided to put it on hibernation to assess the exact condition of fuel and determine how much time the mission has got on its hands.

Kepler’s state of hibernation is similar pretty similar to sleep or safe mode, where most of the instruments are to put on rest to save resources and extend the life of the craft in question.

The hydrazine fuel warming first came up when Kepler was on its 18th observational campaign, looking toward the constellation of Cancer. The project was disrupted, prompting the agency to place it on hibernation and prepare for downloading the scientific data the spacecraft had collected.

As data transmissions from space missions occur only at a certain Deep Space Network time, Kepler was awakened from its sleep Aug. 2. The telescope successfully made contact and corrected its orientation to point antennas back to Earth and beam the data from Campaign 18 over the next week.

Originally, the spacecraft was scheduled to begin Campaign 19 on Aug. 6, but that didn’t happen, and on Aug. 24, NASA announced they had to put the telescope back into sleep. The agency said the fuel situation still remains unclear, but as Kepler sleeps, they are looking at the health of the telescope and working out the range of options and next steps to be taken.

As per the preliminary analysis and signs of fuel noted till date, Kepler could run out of propellant within the next few months, which would effectively mark the end of its mission.

The era of exoplanet discovery

The $600 millions’ worth Kepler space telescope marked a new era of exoplanetary science after launching into the skies in March 2009. Over this period, it scoured cosmic regions and discovered more than 2,650 Earth-sized and bigger exoplanets around distant stars.

Kepler’s technique to find planets beyond our own solar system revolves around looking for occasional dips or "transits" in the light of distant stars. These changes signify the presence of an orbiting world, one that is coming between Kepler’s view and the star in question, blocking some of its light.

Kepler’s preliminary mission was to look at a batch of 150,000 stars, but the mission ended in 2013 due to a problem in the spacecraft’s orientation-assisting reaction wheels. When the agency found a way to stabilize its condition, the second phase of the mission, called K2, began. As part of this, the telescope has been conducting 80-day-long observational campaigns while looking different patches of the sky.