MeasurementBlog

Kepler is NASA’s first mission capable of finding Earth-size and smaller planets around other stars.

The Kepler Mission, a NASA Discovery mission, is specifically designed to survey our region of the Milky Way galaxy to detect and characterize hundreds of Earth-size and smaller planets in or near the habitable zone. The habitable zone encompasses the distances from a star where liquid water can exist on a planet’s surface.

Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy.

Read all about the background and the planned measurement methods: at Frequently Asked Questions.

The key factors used to achieve the required differential performance for the Kepler Mission are:

* Differential spatial photometry: The brightness of each target star is normalized to the average of all nearby stars, providing common-mode rejection in the measuring system.

* Differential temporal photometry: Transit durations are a few hours to less than about half of a day. Brightnesses are compared to data just shortly before and after the test interval, so there is no need for long term stability.

* Decorrelation of image motion: Motion due to the image drifting over time scales long compared to a transit produce highly correlated amplitude variations that are removed.

* Optimal weighting of pixels: The individual pixels that comprise each star image are weighted to maximize the SNR.

* Keeping each star image on the same pixels for three months: Eliminates effects of inter- and intra-pixel quantum-efficiency variations.

* Operating the CCDs near full well capacity: Read noise and dark current are negligible.

* Selection of an Earth-trailing heliocentric orbit: Stable thermal environment and negligible scattered light background.

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