The scientific goal of the Kepler Mission
is to explore the structure and diversity of planetary systems.
More specifically, this is achieved by observing a large sample
of stars to:
Goal 1: Determine the frequency
of terrestrial and larger planets in or near the habitable zone
of a wide variety of spectral types of stars.
The frequency of planets is derived from the number and size
of planets found and from the number and spectral type of stars
monitored. Even a null result would be highly meaningful because
of the large number of stars searched and the low false alarm
Goal 2: Determine the distributions
of sizes and orbital semi-major axes of these planets.
The planet's area is found from the fractional brightness decrease
and the stellar area. For a detection with a statistical significance
of >8 sigma, the uncertainty of the planetary area is about
14% and the planetary radius to 7%.
The planet's semi-major axis is derived from
the measured period and stellar mass, using Kepler's Third Law.
An uncertainty in the semi-major axis of about 1% results from
a 3% uncertainty in the mass of the central star, derived from
ground-based spectroscopic observations.
Goal 3: Estimate the frequency
of planets and orbital distribution of planets in multiple-stellar
This goal is achieved by comparing
the number of planetary systems found in single versus multi-star
systems. Multiple-stellar systems are identified from ground-based
spectroscopic measurements if they are tightly bound or from
high angular resolution observations if they are widely spaced
Goal 4: Determine the distributions
of semi-major axis, albedo, size, mass and density of short-period
Short-period giant planets are detected from variations in their
reflected light. As above, the semi-major axis is derived from
the orbital period and the stellar mass.
Transits should also be seen in about 10%
of the cases and the size of the planet determined. These planets
are found in the first few months of the mission. From the planet
size, semi-major axis and the amplitude of reflected light modulation,
the albedo is determined. The density is calculated when the
planet is seen both in transit (to yield its size) and when Doppler
spectroscopy is used (to determine the planet's mass for stars
with mv<13 and cooler than
F5) as was done for the case of HD209458b.
Goal 5: Identify additional
members of each photometrically discovered planetary system using
Observations using both the Space
Interferometry Mission (SIM) and ground-based Doppler spectroscopy
are used to search for additional massive companions which do
not transit, thereby providing greater details of each planetary
Goal 6: Determine the properties
of those stars that harbor planetary systems
The spectral type, luminosity class,
and metalicity for each star showing transits are obtained from
ground-based observations. Additionally, rotation rates, surface
brightness inhomogeneities and stellar activity are obtained
directly from the photometric data. Stellar age and mass
is determined from Kepler p-mode measurements.
Support for Origins Theme Missions:
Further, the results of the above stated Goals
support the 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 and
- Providing a list of targets for SIM where systems are already known to have terrestrial planets.