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Kepler spacecraft goes into emergency mode

NASA's planet-hunting Kepler probe has entered its lowest operational mode as NASA scientists try to determine what is wrong with it.

Artist's impression of the Kepler spacecraft looking for planets.

The Kepler space observatory has officially entered emergency mode, NASA has reported, which means planet-hunting operations are low priority while the terrestrial team tries to diagnose the craft and bring it back to capacity.

The last contact previous to this check-in was on April 4, at which time Kepler was operating at capacity.

Kepler was originally launched in 2009, and its mission, hunting for exoplanets, was expected to run for three and a half years. However, NASA quickly found that the mission would take more time than that, and the mission was extended until 2016.

However, in 2012 and 2013, two of the observer's four reaction wheels failed, and the mission was modified to search primarily for planets around smaller, dimmer red dwarf stars. This extended K2 mission commenced in 2014.

Before Kepler went into emergency mode, it was about to commence the ninth campaign of the K2 mission, looking for planets in the direction of the centre of the Milky Way galaxy. This campaign is now delayed.

Kepler is currently over 120 million kilometres (75 million miles) from Earth, which makes communicating with the spacecraft difficult.

"Even at the speed of light, it takes 13 minutes for a signal to travel to the spacecraft and back," mission manager Charlie Sobeck explained.

To date, Kepler has identified 1,963 confirmed exoplanets of 4,696 exoplanet candidates.