NASA’s Kepler planet-hunting space telescope resumed science operations March 20 after spending six days stuck in a protective safe mode while engineers studied the computer glitch.

An anomaly response team will continue to evaluate the spacecraft data to determine the cause of the safe mode event, Kepler mission managers explained in a March 21 written update.

The glitch occurred March 14, when Kepler’s on-board systems ordered the spacecraft’s network interface card to begin a computer program update. The card is a key component in Kepler’s subsystem interface box and provides a link between the space observatory’s flight software, attitude control and other sensors and control subsystems, mission managers said.

While Kepler’s computer program was updating, the network interface card sent faulty data to the spacecraft’s flight software, sending the observatory into safe mode.

Safe mode is a hibernation-like state that spacecraft enter when their on-board computer detects an operational state or malfunction that it is not able to solve on its own. During the event, Kepler shut down all non-essential systems and orientated itself to point its solar arrays at the sun.

“This safe mode orientation provides the vehicle with the maximum power and limits the buildup of momentum from solar wind,” Kepler mission managers said.

NASA launched the $600 million Kepler observatory in 2009 to seek out alien planets that circle other stars.

To do that, the spacecraft is staring continuously at a single patch of the sky, watching for tiny changes in the amount of light coming from every star it sees — a sign of a potential planet crossing (or transiting) in front of its parent star, as seen by Kepler. Astronomers use other telescopes to follow up Kepler’s findings in order to confirm whether or not the candidate stars do, in fact, host exoplanets.

To date, Kepler has discovered 1,235 possible planets, with 54 of those candidates located within the so-called Goldilocks zone — a just-right habitable zone around a star in which liquid water could exist on a planet’s surface.

Based on the wealth of planet candidates from Kepler, astronomers have estimated that the Milky Way galaxy could hold as many as 50 billion alien planets, with 2 billion of those being about the size of Earth.

The Kepler spacecraft was built by Boulder, Colo.-based Ball Aerospace & Technologies Corp. under NASA’s Discovery program of scientist-led missions.