NASA engineers are scrambling to diagnose and fix their planet-hunting Kepler spacecraft after it unexpectedly switched to an emergency mode — its lowest operational, albeit fuel-guzzling, mode — last week. The spacecraft, which has discovered over 1,000 exoplanets since it was launched in 2009, is currently at a distance of nearly 75 million miles from Earth.

“The last regular contact with the spacecraft was on April. 4. The spacecraft was in good health and operating as expected,” Charlie Sobeck​, Kepler mission manager, said in a brief statement released Saturday. “During a scheduled contact on Thursday, April 7, mission operations engineers discovered that the Kepler spacecraft was in Emergency Mode. ... Initial indications are that Kepler entered EM approximately 36 hours ago, before mission operations began the maneuver to orient the spacecraft to point toward the center of the Milky Way for the K2 mission's microlensing observing campaign.”

So far, Kepler has detected exoplanets — planets outside our solar system — by looking for periodic dimming in their parent stars’ light. Although this technique has proven to be wildly successful and has yielded 1,040 confirmed discoveries and over 4,500 candidates, it does not work so well for planets whose orbits are too far from their parent star to cause significant dimming, or for free-floating exoplanets wandering the cosmic void between stars.

The microlensing observing campaign, part of Kepler’s extended K2 mission, aims to detect distant exoplanets by detecting the warping effect of gravity on light, called gravitational lensing.

“This first-of-its-kind survey serves as a proof of concept for NASA’s Wide-Field Infrared Survey Telescope (WFIRST), which will launch in the 2020s to conduct a larger and deeper microlensing survey,” Paul Hertz, director of the astrophysics division in NASA’s Science Mission Directorate, explained. “In addition, because the Kepler spacecraft is about 100 million miles from Earth, simultaneous space- and ground-based measurements will use the parallax technique to better characterize the systems producing these light amplifications.”

For now, though, the mission is on hold as scientists attempt to get the telescope working again.

This is not the first time the spacecraft, which completed its primary mission in November 2012, has run into trouble. Between July 2012 and May 2013, two of its gyroscope-like reaction wheels, which were used to precisely orient the spacecraft, failed. Then, in November 2013, NASA announced Kepler’s secondary mission — the K2. Since then, the spacecraft has been utilizing the two remaining wheels and the tiny pressure exerted by sunlight to balance itself and carry out observations.