The Kepler space telescope is almost out of fuel, which means that its life is coming to an end, NASA announced today. The space agency says it placed the planet-hunting spacecraft in a safe mode of "hibernation" last Monday, and that a plan to reactivate Kepler next month could burn the remaining fuel.
NASA launched the Kepler Space Telescope in 2009 in an effort to learn more about the number and frequency of planets in our galaxy. To the delight of many, scientists using Kepler have found a large number of exoplanets or planets outside our solar system. The spacecraft, which is about 94 million miles away from Earth, has scanned only a small section of our galactic neighborhood, but its efforts have led scientists to discover 2,650 planets confirmed so far.
They have come in all shapes and sizes, too. The planets that researchers have appeared vary from large and strange, such as a planet the size of Jupiter in orbit around a binary star system, to those with a size and orbit closer to Earth. Each discovery has taught us more about how planets are formed, how many types of planets there are, and even how our planet came to be. And many rewards are still found in Kepler's generosity. There are thousands of other unconfirmed discoveries, and researchers continue to find new ways to delve into Kepler's data.
NASA says it plans to restart Kepler in early August, when it will order the spacecraft to aim its antenna at Earth to download the data from its most recent study of the sky. It is not clear if there is enough fuel to make that transfer. However, once the transfer is complete, NASA plans to begin what will be the 19th discreet "observation campaign" of Kepler's "K2" secondary mission, which began in 2014. The maneuvers necessary to point the antenna towards the Earth are the most fuel-intensive that Kepler performs, and at any point, the spacecraft's tank could eventually be depleted.
NASA knew that Kepler would one day run out of fuel, and when the K2 mission began, the agency originally predicted being able to extract only 10 observation campaigns from what was left in the tank. But putting the spacecraft in safe mode is a sign that Kepler is really working with gases. So now, "returning data to Earth is the top priority for the remaining fuel," says NASA.
Kepler has gone into hibernation before, and the space telescope has encountered a lot of problems in its nine years of operation. When it slid into a similar mode in 2016, it caused NASA to declare a temporary "space vehicle emergency" as the team worked to put the telescope back online.
But Kepler's biggest problem was in 2012, when two of the telescope's four gyroscopic "reaction wheels" stopped working. The impulse generated by these wheels was used to make fine adjustments in the orientation of the telescope. Losing one was fine, but losing two was a possible death sentence. Kepler had already completed his initial mission, and it seemed that NASA could stop the operation of the telescope, until an intelligent solution emerged within the agency to use the pressure exerted by the sun's rays on the solar panels of the ship as a substitute for the one of the wheels. That solution gave Kepler his second life with the K2 mission, which still works today.
NASA has already launched a successor to Kepler, so even when it dies, the search for exoplanets will continue. The satellite Transiting Exoplanet Survey Satellite, or TESS, took a flight from the planet in a SpaceX Falcon 9 earlier this year, and has already broken its first galactic sky image. TESS has a field of vision 400 times larger than Kepler, which will allow you to study hundreds of thousands of stars more than its predecessor. TESS will also search for planets around stars that are tens or hundreds of light-years away from us, unlike Kepler, who studied stars thousands of light-years from our solar system.