The Kepler mission will be the first serious attempt to discover Earth-like planets around other stars in our Milky Way galaxy. Designed as an orbiting space telescope, Kepler is the eighth and most recently approved mission of NASA's ambitious Discovery Program. The final price tag of the mission will be around $299 million, which is the cap for missions in the Discovery Program.

Transit method

Astronomers have discovered 80 or so large gas planets around other stars, however a small, solid terrestrial planet has yet to be discovered. This is partly because current ground-based and space-based telescopes, including Hubble, do not have the sensitivity to detect them. To discover extrasolar planets, scientists use the transit method. When a planet moves in front of the star it is orbiting, it blocks some of the star's light. This decrease in luminosity can be detected and used to compute the size and orbit of the planet. Until now, we have only been able to discover large gaseous planets such as our sun's Jupiter. The Kepler mission will utilize a telescope so powerful that it can detect changes in the light of a star of 1/100th of a percent. It will stare at the same point in the constellation Cygnus and track up to 100,000 stars simultaneously. In order to avoid statistical bias, no star in this region will be discounted from observation, even if it is considered too large or too small to host Earth-like planets. Most current theories of planet formation suggest the stars with the highest probability of possessing solid, inner terrestrial planets are about the size of our sun. Many believe large gas planets are a critical part in the formation of small planets in a solar system small, as they may act as a shield for the inner sanctum by gravitationally taking care of comets, asteroids, and other planet-busting intruders. Scientists predict that most sun-like stars have one to two inner planets, and they expect to find hundreds of these worlds during its five year long data collection period.

Habitable zones

In 1993, Kasting, Whitmore, and Reynolds proposed the boundaries of a so-called habitable zone around a given star where liquid water is most likely to exist. The Kepler mission will focus on discovering planets within this zone. The calculation of this zone is tailored for an individual star's size and intensity. Still, theorists are not certain that water is critical for the formation of life. Based on the number of planets found in habitable zones, researchers will be able to refine the infamous Drake equation. Currently, there is no evidence of how common terrestrial, habitable planets are in the universe, or even the galaxy. This number is a critical part of the Drake equation, which seeks to predict the number of intelligent civilizations in the universe.

Onboard instrumentation

Encircling the globe in an Earth-trailing heliocentric orbit, the Kepler mission will employ an enormous 95 centimeter photometer incorporating a primary mirror with a diameter of 1.5 meters. This allows the planet-seeking contraption a constant field of view of about 10 degrees by 10 degrees, resulting in a 100 degree "square of sky." To block the blinding intrusion of the sun, Kepler will sport a movable sun shield. Data collected are sent back instantaneously to Earth via a High-Gain antenna to be analyzed by ground computers. The mathematical examination of this information should result in frequent discoveries of extrasolar planets over the mission's five year life span.

Johannes Kepler

NASA has always been quite fond of naming missions and their spacecraft after historical figures in the field of astronomy and mathematics. (See: Galileo probe, Hubble Space Telescope, Cassini probe, Huygens probe) The Kepler mission is named after Johannes Kepler, the famous 17th century astronomer credited with discovering the three laws of planetary motion, first published in 1609 and 1619. You might remember from grade school his famous edict that planets "sweep out equal areas in equal times." Interestingly, Kepler was reluctant to give up his vision of a perfect and crystalline universal geometry for the uneven and oblong reality of the solar system, perhaps in much the same way many will have to one day grudgingly admit that other beings inhabit other earths around other suns.

Critical Mission Dates

  • October 2007 - Launch

  • November 2007 - Begin data collection

  • November 2012 - End data collection

Habitable Zones around Main Sequence Stars, JF Kasting, DP Whitmire, RT Reynolds, Icarus, 101, 108-128 (1993)

Other NASA Discovery Program Missions
·Mars Pathfinder·
·Lunar Prospector·
·Deep Impact·

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