The search for planets orbiting other stars has reached industrial scale. Astronomers have discovered over 4,000 of them, more than half using data from the Kepler space telescope, an orbiting observatory designed for this purpose.

Launched in 2009, Kepler observed a fixed field of view for many months, looking for the tiny periodical changes in stars’ brightness caused by planets moving in front of them.

But in 2012 the mission ran into trouble when one of the spacecraft’s four reaction wheels failed. These wheels stabilize the craft, allowing it to point accurately in a specific direction. In 2013, a second reaction wheel failed, leaving the mission in jeopardy.

As a fix, engineers devised a way for the crippled spacecraft to continue gathering data with less precision and more noise. They called this part of the mission K2. Astronomers continued to find new exoplanets in the K2 data, but at a much lower rate than before. READ MORE ON: MIT TECHNOLOGY REVIEW