It’s safe to say that without the Kepler telescope, our knowledge of planets beyond the Solar System would be a fraction of what it is today. And now the mission is sadly reaching its conclusion.
On Friday, July 6, NASA said that the spacecraft had been placed in hibernation, as its fuel reserves were “running very low”. We’ve known for a while that the telescope was running out of fuel, but now it looks like we’re moving towards the end-game.
The spacecraft has recently been on its 18th observation campaign, looking at stars towards the constellation of Cancer to hunt for planets. It does this by watching for dips in the light of the stars, known as the transit method, caused by orbiting planets passing in front of the stars.
It has actually looked at this patch of sky before, back in 2015. But to confirm planets it needs to see three transits, so it looked again to try and verify some of the candidate planets spotted three years ago.
At the moment we don’t know what it found, because the data from the telescope is still on board. To send the data back to Earth, Kepler has to use fuel to fire its thrusters and point its antenna back towards our planet.
It has been allocated time on the Deep Space Network, a global array of dishes that receives data from spacecraft, in early August. So until then, NASA will keep the spacecraft in a “no-fuel-use” safe mode, to ensure it has enough fuel to point towards us.
“On August 2, the team will command the spacecraft to awaken from its no-fuel-use state and maneuver the spacecraft to the correct orientation and downlink the data,” said NASA. “If the maneuver and download are successful, the team will begin its 19th observation campaign on August 6 with the remaining fuel.”
Kepler has already returned a huge amount of data, which scientists are currently poring through. They’re still only sifting through the 10th observation campaign, meaning that even when the mission ends, it will take years to go through the remaining data.
So far the telescope has found more than 2,300 confirmed exoplanets, with thousands more candidate planets. Since March, though, we’ve known the spacecraft was nearing its end. It was just a matter of time until the mission came to an end.
Positioned 151 million kilometers (94 million miles) from Earth, the spacecraft cannot be refueled. So when it does eventually run out, we’ll be saying goodbye to this pioneering mission. It will be succeeded by the Transiting Exoplanet Survey Satellite (TESS), which launched in April. But Kepler will be sorely missed, leaving behind a fascinating legacy that enhanced our knowledge of exoplanets forever.