The Kepler Telescope’s decade-long run comes to an end

Unfortunately, the reign of the first ever spacecraft sent to search for unknown planets has ended. The Kepler Space Telescope has fallen subject to every couples’ road-trip nightmare: it’s run out of fuel, very far from a filling station. NASA has known this would happen for a while but it’s used this time well, making Kepler send back as much information as possible prior to its inevitable fate.

Kepler’s 12 kilograms (just over 3 gallons) of hydrazine fuel allowed the spacecraft to travel a whopping 94 million miles from Earth over the last nine-and-a-half years. In case you’re wondering, that’s roughly 31.3 million miles to the gallon – slightly better than your average Prius.

As its current path is clear of both Earth and sensitive environments, NASA continued to use the remaining fuel to send back as much information as possible until its reserves ran dry. The last commands Kepler will receive will order it to disable its on-board fault protection software and turn off its transmitters. Thereafter, it will drift through space.

Throughout its time Kepler used a technique called the “transit method” to discover planets. This method uses light detecting sensors called photometers. These photometers monitor alterations in the light coming from stars, discerning whether these changes came from planets passing across them and, if so, how large they were. Borucki describes this like “trying to detect a fly crawling across a car headlight when the car was 100 miles away. And the instrument must do it for 150,000 stars simultaneously.”

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Launched in March 2009, Kepler observed over 5,000 potential and confirmed planets in the Cyrnus and Lyra constellations. Of which, two to 12 are deemed Earth-sized and within the estimated distance from a star to hold water. This means that, although Kepler will be shutting down, its findings have paved the way for the delayed James Webb Space Telescope mission set to launch in 2021. The James Webb Space Telescope has the capability to study atmospheres – a crucial aspect to concluding if these Earth-like planets can support life.

For now, NASA’s latest mission, the Transiting Exoplanet Survey Satellite (TESS), which launched in April, will continue to use the transit method to explore the stars and their respective planets in the wake of Kepler’s retirement.

During its operational lifetime, the Kepler telescope led to the discovery of 2,681 planets, observed 530,000 stars, and drew attention to 2,899 other potential planets. To put that into perspective, just in case you’d forgotten, our solar system has eight planets – and one star. Understandably, Bill Borucki, the retired astronomer responsible for leading Kepler’s science team from its earliest days, has boasted that his spacecraft has found planets which have been around since the forming of our galaxy, some six-and-a-half-billion years ago. He has also personally re-categorized our solar system to be “atypical”.

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NASA has said that Kepler was “a wonderful success”, noting that it’s survived twice its designed time, surpassed technical faults, and has been literally “blasted” by cosmic rays. Jessie Dotson, Kepler Project Scientist at Ames, has referred to Kepler as a spacecraft which did all it was asked and sometimes more.

Kepler’s contribution to space exploration has helped to write over 3,000 papers – with numerous still to come as the final findings are reviewed. To quote The Hitchhiker’s Guide To The Galaxy, “Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is.” But because of Kepler’s efforts, it’s a little less big.