Kepler (Discovery 10)

Kepler [NASA]

The scientific goal of the Kepler Mission is to explore the structure and diversity of planetary systems. This is achieved by surveying a large sample of stars to:

• 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 semi-major axes of these planets;
• Estimate the frequency and orbital distributions 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; and
• Determine the properties of those stars that harbor planetary systems.

Transits by terrestrial planets produce a fractional change in stellar brightness of 5 x 10^-5 to 40 × 10^-5 lasting for 2 to 16 hours. The orbit and size of the planets can be calculated from the period and depth of the transit.

The Kepler instrument is a 0.95-meter aperture differential photometer with a 105 deg² field of view. It continuously and simultaneously monitors brightnesses of 100,000 A-K dwarf (main-sequence) stars brighter than 14th magnitude. The experiment is not biased by preselection of stellar type or single versus multiple star system.

The Kepler photometer is a simple single purpose instrument. It is basically a Schmidt telescope design with a 0.95-meter aperture and a 105 deg2 (about 12 degree diameter) field-of-view (FOV). It is pointed at and records data from just a single group of stars for the four year duration of the mission.
The photometer is composed of just one "instrument," which is, an array of 42 CCDs (charge coupled devices). Each 50 × 25 mm CCD has 2200 × 1024 pixels. The CCDs are read out every three seconds to prevent saturation. Only the information from the CCD pixels where there are stars brighter than mv=14 is recorded. (The CCDs are not used to take pictures. The images are intentionally defocused to 10 arc seconds to improve the photometric precision.) The data are integrated for 15 minutes.

Launch is planned for June 2008.