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KEPLER The Planet find Mission. NASA's first mission capable of finding Earth-size and smaller planets around other stars. Kepler Overview. The question of is there other worlds has been answered. There is now clear evidence for substantial numbers of three types of exoplanets ;
The Planet find Mission
NASA's first mission capable of finding Earth-size and smaller planets around other stars
Kepler'sthird law, which is often called the harmonic law, is a mathematical relationship between the time it takes the planet to orbit the Sun and the distance between the planet and the Sun. The time it takes for a planet to orbit the Sun is its orbital period, which is often simply called its period. For the average distance between the planet and the Sun, Kepler used what we call the semi-major axis of the ellipse. The semi-major axis is half the major axis, which is the longest distance across the ellipse. Think of it as the longest radius of the ellipse.
Illustration of Kepler's three laws with two planetary orbits. (1) The orbits are ellipses, with focal points ƒ1 and ƒ2 for the first planet and ƒ1 and ƒ3 for the second planet. The Sun is placed in focal point ƒ1. (2) The two shaded sectors A1 and A2 have the same surface area and the time for planet 1 to cover segment A1 is equal to the time to cover segment A2. (3) The total orbit times for planet 1 and planet 2 have a ratio a13/2 : a23/2.
Newton's Form of Kepler's Third Law
M1 + M2 = A3 / P2
Solar Mass 1 + Solar Mass 2 = Astronomical Units 3 / Orbit Years 2
Kepler Focal Plane Array
The focal plane consists of an array of 42 charge coupled devices (CCDs). Each CCD is 2.8 by 3.0 cm with 1024 by 1100 pixels. The entire focal plane contains 95 mega pixels. Credit: NASA and Ball Aerospace
Since transits only last a fraction of a day, all the stars must be monitored continuously, that is, their brightnesses must be measured at least once every few hours. (We must sum the light accumulated in this time to obtain a statistically significant measurement). The ability to continuously view the stars being monitored dictates that the field of view (FOV) must never be blocked at any time during the year. Therefore, to avoid the Sun the FOV must be out of the ecliptic plane.
The payload envelope of the launch vehicle limits the sunshade size and hence the target field to be >55º from the ecliptic plane. The secondary requirement is that the FOV have the largest possible number of stars. This leads to the selection of a region along the Cygnus arm of our Galaxy as shown.
To meet the goals of making statistically meaningful conclusions, the mission design should be such at least 45 terrestrial planets (R<1.3 Re) are expected, requiring many thousands of stars to be observed simultaneously in one FOV. (Continuously re-orienting the photometer to view fewer bright stars in many different fields-of-view (FOV) increases the mission complexity and cost and is less efficient than using a single FOV.)
A region of the extended solar neighborhood in the Cygnus region along the Orion arm centered on galactic coordinates (76.32º,+13.5º) or RA=19h 22m 40s, Dec=+44º 30' 00' has been chosen.
The star field is far enough from the ecliptic plane so as not to be obscured by the Sun at any time of the year. This field also virtually eliminates any confusion resulting from occultations by asteroids and Kuiper-belt objects. Comet-size objects in the Oort cloud subtend too small an angular size and move too rapidly to be a problem.
Based on the model of stellar distribution and dependence of detectable planet size on stellar type and brightness, the number and type of stars monitored as a function of planet size is shown in the figure.
For all candidate transit cases, complementary follow-up observations are made to confirm that the transits are due to planets and to learn more about the characteristics of the parent stars and planetary systems.
All known 400+ exoplanets as of Dec 2009 plus the 5 new planets found with Kepler. The green band represents the parameters for habitable planets. Too close to the Sun and water vaporizes. Too far from the Sun and water freezes. Too low of a mass, and the planet does not have enough surface gravity to hold onto a life sustaining atmosphere. Too large of a mass and the planet has enough gravity to hold onto the most abundant element in the universe, hydrogen, and become a gas-giant planet.
Two common types of astrophysical phenomena that can masquerade as a planetary transit are grazing eclipsing binaries (left), where a pair of stars orbit each other, and background eclipsing binaries (right), where a distant binary star system is aligned very close to the star of interest. These require significant amount of ground-based observations to eliminate using radial velocity techniques
In the first 43 days of data-taking, Kepler found about 175 transit candidates.
Lots more planets are coming — probably hundreds by the time the mission is scheduled to end three years from now.
Any such planet has only a 1-in-200 chance of being in an orbit that's oriented just right to cross a Sun-sized host star as seen from our viewpoint. That's one reason why Kepler is watching so many stars.Another is statistics. Kepler is intended not just to identify a few individual exo-Earths. It was designed to watch enough stars to give a firm statistical reading on the abundance — or rarity — of terrestrial-size planets generally, throughout the galaxy and the universe.
A star’s placement on the detector’s array of pixels yields its position to better than a thousandth of a pixel-width, or 4 milliarcseconds.