NASA’s Kepler Mission will be able to find planets the size of Earth and even smaller that are orbiting in the habitable zone of other stars similar to our Sun. Kepler is specifically designed to survey our region of the Milky Way galaxy to discover hundreds of Earth-size and smaller planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets.

The Kepler Mission was launched on Friday, March 6, 2009. Liftoff occurred on time at 10:49pm EST from Cape Canaveral Air Force Station in Florida. The mission will last for three and one-half or more years, to enable the detection of three to four transits for each planet in the habitable zone of a star.


For the first time in human history, we will know if there are Earth-size planets capable of supporting life beyond our solar system. Kepler supports scientific objectives, as well as the objectives of future NASA Origins theme missions.

Specific goals and objectives of the Kepler Mission include:

  • Determine the frequency of terrestrial and larger planets in or near the habitable zone of a wide variety of spectral types of stars.
  • Determine the distributions of sizes and orbital semi-major axes of these planets.
  • Estimate the frequency of planets and orbital distribution of planets in multiple-stellar systems.
  • Determine the distributions of semi-major axis, albedo, size, mass and density of short-period giant planets.
  • Identify additional members of each photometrically discovered planetary system using complementary techniques.
  • Determine the properties of those stars that harbor planetary systems. [1]

The Kepler Mission also supports the objectives of future NASA Origins theme missions, the Space Interferometry Mission (SIM), and the Terrestrial Planet Finder (TPF) by:

  • Identifying the common stellar characteristics of host stars for future planet searches.
  • Defining the volume of space needed to search.
  • Providing a list of targets for SIM where systems are already known to have terrestrial planets. [2]


The Kepler Mission is supported by several individuals affiliated with NASA Ames Research Center. More specifically, the Kepler Project Office, Kepler Science Office, and Kepler Science Operations Center (SOC) are all located at the NASA Ames Research Center. The Kepler Science Team includes co-investigators associated with NASA Ames Research Center, University of California-Berkeley, San Jose State University, Las Cumbres Observatory Global Telescope (LCOGT), SETI Institute, McDonald Observatory, Aarhus University, Lowell Observatory, Jet Propulsion Laboratory, Smithsonian Astrophysical Observatory, Space Telescope Science Institute, NASA Goddard Space Flight Center, Harvard Smithsonian Astrophysical Observatory, U.S. Naval Observatory, and Harvard-Smithsonian Center for Astrophysics.

The Kepler Science Team also encompasses a Science Working Group, which includes scientists affiliated with the Carnegie Institution of Washington Department of Terrestrial Magnetism, Harvard Smithsonian Astrophysical Observatory, York University, NexSci Caltech, Aarhus University, Harvard-Smithsonian Center for Astrophysics, NASA Ames Research Center, SETI Institute, and Villanova University.

Additional participating scientists contributing to the Kepler Science Team include those affiliated with Eureka Scientific, Harvard-Smithsonian Center for Astrophysics, Massachusetts Institute of Technology, SETI Institute, Fermilab, University of Florida, San Diego State University, and University of California-Santa Cruz.

There are additional Kepler project teams within the NASA Jet Propulsion Laboratory, Laboratory for Atmospheric and Space Physics (LASP), Ball Aerospace, Deep Space Network, and the Space Telescope Science Institute (STScI). This is not intended to reflect a comprehensive list. [3]


The Kepler instrument is a 0.95-meter diameter telescope which is referred to as a photometer or light meter. The telescope has a very large field of view for an astronomical telescope—105 square degrees. As a basis for comparison, the field of view for most telescopes is less than one square degree. The Kepler instrument requires a large field of view in order to observe the large number of stars. The instrument views the same star field for the entire mission, continuously monitoring the brightness of more than 100,000 stars for at least 3.5 years.

The diameter of the Kepler telescope must be large enough in order to reduce the noise from photon counting statistics, so that it is capable of measuring the small change in brightness of an Earth-like transit. The system is designed in such a way that the combined differential photometric precision over a 6.5 hour integration is less than 20 ppm (one-sigma) for a 12th magnitude solar-like star, including an assumed stellar variability of 10 ppm. [4]

Expected Outcomes

Results from the Kepler Mission are broken down into the following categories, based on method. These expectations are based on conservative assumptions regarding detection criteria, stellar variability, taking into account only orbits with four transits in 3.5 years, and the assumption that planets are common around other stars (like our Sun).

From transits of terrestrial planets in one year orbits:

  • About 50 planets if most are the same size as Earth (R~1.0 Re) and none larger.
  • About 185 planets if most have a size of R~1.3 Re.
  • About 12% with two or more planets per system. [5]

From transits of giant planets:

  • About 135 inner-orbit planet detections.
  • Densities for 35 inner-orbit planets.
  • About 30 outer-orbit planet detections. [6]


  • As of September 2018, the Kepler Mission had 2,344 confirmed planets, 290 candidates and confirmed in a habitable zone, 4,696 Kepler project candidates, and 2,244 Kepler project unconfirmed candidates. The total number of candidates and confirmed planets is 4,588. [7]
  • The mission has also discovered the first Earth-sized planets, as well as the first small planet in the habitable zone. Kepler has confirmed a new class of double-star planetary systems, as well as the first multiple-transiting planet system, and has identified the first rocky planet. In August 2012, the Kepler mission discovered multiple transiting planets orbiting two suns for the first time. Known as a circumbinary planetary system, this system is 4,900 light-years from Earth, located in the Cygnus constellation. The discovery of such a system proves that more than one planet can form and persist in the realm of a binary star. [8]
  • In February 2014, the mission announced the discovery of 715 new planets. These worlds orbit 305 stars, revealing multiple-planet systems much like our own solar system. Almost 95 percent of the newly-verified planets are smaller than Neptune. [9]
  • In April 2014, Kepler discovered the first Earth-size planet orbiting a star in the “habitable zone,” Kepler-186f. This discovery confirms that planets the size of Earth exist in the habitable zone of stars other than our Sun. Planets had previously been found to exist in the habitable zone, but all were significantly larger than Earth – most by about 40 percent. The discovery of Kepler-186f represents the discovery of an Earth-like planet, which is less challenging when it comes to understanding its makeup. [10]
  • In January 2015, using data from the Kepler mission, astronomers discovered an ancient planetary system that dates back to when the Milky Way galaxy was only two billion years old. This system, Kepler-444, has five planets that range in size – the smallest planet is comparable to Mercury, while the largest is similar to Venus. The system is very tightly packed, with all five planets orbiting their sun-like star in under 10 days. [11]
  • In July 2015, NASA’s Kepler team announced the discovery of planet Kepler-452b, which has the closest match of planet characteristics to Earth. The planet is 60% larger than Earth and orbits a Sun-like star in a 385 day orbit period, placing it in the star’s habitable zone. [12]
  • In July 2015, NASA first announced 12 new small Kepler habitable zone candidates. These 12 new planet candidates are from the seventh Kepler planet candidate catalog that are less than twice the size of Earth and orbit in the stars’ habitable zone. [13]
  • In May 2016, the Kepler Mission announced the largest collection of planets ever discovered. Approximately 550 of the 1,284 new Kepler planets are small possibly rocky, with nine of those residing in the habitable zone. [14]
  • In June 2016, a team of astronomers from NASA’s Goddard Space Flight Center and San Diego State University used NASA’s Kepler Space Telescope to identify the new planet, Kepler-1647b. This planet is 3,700 light-years away and approximately 4.4 billion years old. The planet has a mass and radius nearly identical to that of Jupiter, making it the largest transiting circumbinary planet ever found. [15]
  • March 2018 news indicated that the while the Kepler was continuing to bring exciting data, it was drawing close to the finish line, as fuel began running low. [16]
  • August 24, 2018 sources indicated that the Kepler spacecraft had gone into sleep mode, but then was roused from sleep mode on August 29th, to begin the spacecraft’s 19th observation campaign involving data collection. September 5th, 2018 sources indicate that the spacecraft’s configuration has been modified due to unusual behavior exhibited by one of the thrusters and that preliminary indications were that the telescope’s pointing performance may be somewhat degraded. The source notes that it remains unclear how much fuel remains and that NASA will continue to monitor the health and performance of the spacecraft. [17]

NASA Exoplanet Archive

The NASA Exoplanet Archive is an online astronomical exoplanet and stellar catalog and data service that collates and cross-correlates astronomical data and information on exoplanets and their host stars, providing tools to work with this data. The Exoplanet Archive lists all known planets and hosts, all Kepler Objects of Interest, and all Kepler Threshold-Crossing Events. [[18]] The NASA Exoplanet Archive is accessible through this website.

Updated September 2018 by Theresa Pipher

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