Mission Overview

Kepler is NASA's first mission capable of finding Earth-size and smaller planets. The Kepler mission, scheduled to launch in 2009, will monitor the brightness of stars to find planets that pass in front of them during the planets' orbits. During such passes or 'transits,' the planets will slightly decrease the star's brightness. Measuring this brief dimming will help scientists detect Earth-size and larger planets in or near the habitable zone (HZ), where liquid water can exist on the planet's surface.


The Kepler mission, scheduled to launch in 2008, will be a space mission to search for Earth-size and smaller planets around other stars in our neighborhood of the galaxy. Scientists also expect to detect larger planets during the mission. Kepler is a special-purpose spacecraft that precisely measures the light variations from distant stars, looking for planetary transits.

When a planet passes in front of its parent star, as seen from our solar system, it blocks the light from that star. This is known as a 'transit.' Searching for transits of distant 'Earths' is like looking for the drop in brightness when a moth flies across a searchlight. Measuring repeated transits, all with a regular period, duration and change in brightness, provides a rigorous method for discovering and confirming planets and their orbits – planets the size of Earth and smaller in habitable zones around other stars. Scientists define habitable zones as volumes in space where planets could be that may well have liquid water on their surfaces.

Kepler will survey four classes of stars – F stars (bigger and brighter than Earth's sun), G stars (similar to our sun in brightness and size) and K and M stars (smaller and less bright than our sun).

Kepler will operate for four years to view an area of the sky 500 times the area of Earth's moon. During this time, Kepler will continuously monitor the brightness of 100,000 stars in the Milky Way galaxy. The Kepler spacecraft consists of a spacecraft bus and a single instrument called a photometer, that is, a light meter, which can simultaneously measure the brightness variations of stars with a precision of about 20 parts per million.

Kepler must measure at least three transits of a planet to consider it a valid planetary candidate. Then, each star with a candidate planet must be observed by ground-based telescopes to eliminate any that have nearby stars that produce a signal that imitates a planetary transit. Consequently, the announcement of planetary discoveries can only be made after a minimum of several months. For Earth-size planets in orbit around stars similar to our sun, we must wait a minimum of three years to get three transits plus the ground-based observing time. Thus, the most valuable discoveries cannot be announced until near the end of the Kepler mission in 2012.

According to researchers, the results will tell scientists how often planets occur in the habitable zone of other stars. If these planets are common, then hundreds of Earth-size planets in the habitable zone and thousands outside the habitable zone will be detected, according to Kepler scientists.

The Kepler mission is a NASA Ames Research Center collaboration with the Space Telescope Science Institute, the Los Cumbre Observatory, the Harvard-Smithsonian Center for Astrophysics, the Lawrence Hall of Science, the SETI Institute, the McDonald Observatory, the University of California at Berkeley, York University, Jet Propulsion Laboratory (JPL), Carnegie Institute, Lowell Observatory, Goddard Space Flight Center, Harvard University, University of Hawaii, University of Washington, National Optical Astronomy Observatory, and Ball Aerospace and Technology Corporation.

Key Mission People
William Borucki, Kepler principal investigator.

David Koch, Kepler deputy principal investigator.

Mike Haas, Kepler science director

Dave Pletcher, Kepler science operations center manager at NASA Ames

Sally Cahill, Kepler business office manager.

Related links:

Kepler Mission Page

Kepler Mission Description

Kepler Featured Image

Ames Researchers Confirm New Technique, Extra-Solar Planet

Images of Kepler Briefing for News Media