The Kepler space telescope

Lore & Background

The Kepler space telescope was developed under NASA's Discovery Program, with construction managed by the Jet Propulsion Laboratory and Ball Aerospace building the flight system. The telescope was placed into an Earth-trailing heliocentric orbit and began surveying a fixed field of view in the Milky Way. After launch, the Ames Research Center handled mission operations and data analysis. The initial planned lifetime was three and a half years, but noise from stars and the spacecraft required additional time. In 2012, one of four reaction wheels failed, and a second failed in May 2013, disabling science data collection. NASA announced on August 15, 2013, that it would not repair the wheels, but the mission was modified into the K2 'Second Light' extension, approved on May 16, 2014, to detect planets around red dwarfs. Kepler's camera had a 94.6-megapixel focal plane made of 42 CCDs, the largest camera system launched into space at the time. Its primary mirror, 1.4 meters in diameter, was made of ultra-low expansion glass and coated with a reflective silver layer. The photometer's performance fell short of design goals, with a median combined differential photometric precision of 29 ppm instead of the target 20 ppm, partly due to higher-than-expected stellar variability.

Reader's Guide

The Kepler space telescope fundamentally changed humanity's understanding of exoplanets by providing the first large-scale census of Earth-sized planets in the Milky Way. Its data enabled estimates that up to 40 billion rocky Earth-size exoplanets may orbit in habitable zones of Sun-like stars and red dwarfs. Kepler also contributed to supernova studies by collecting half-hour light curves. The mission's legacy continues through the TESS telescope, launched in 2018, and through the K2 extension that allowed continued planet hunting after reaction wheel failures. Kepler's discoveries shifted the scientific consensus from uncertainty about planetary systems to a view that planets are common around stars.

Did You Know?

• Kepler was named after Johannes Kepler, who was convinced that planetary systems did not exist around any of the stars.
• The telescope's primary mirror was 1.4 meters in diameter and had a mass only 14% that of a solid mirror of the same size.
• Kepler's camera had a total resolution of 94.6 megapixels, the largest camera system launched into space at the time.