Kepler Orbit

Kepler does not orbit the Earth, rather it orbits the Sun in concert with the Earth, slowly drifting away from Earth. Every 61 Earth years, Kepler and Earth will pass by each other. Throughout the lifetime of the mission, Kepler will point at just one place on the sky in the Cygnus-Lyra constellations. Four times a year, the Kepler spacecraft will make a 90 degree roll about the optical axis to keep the solar array pointed at the Sun and the radiator that cools the detectors pointed to deep space.

Kepler Field of View

The Kepler mission will be looking continuously at over 100,000 stars in one region of the sky, in the Cygnus and Lyra constellations. The field of view is extremely large for an astronomical telescope. Most telescopes such as Hubble Space Telescope only view a small region at one time, about the size of a grain of sand held at arms length.  Kepler covers a much larger field, about an hand at arm’s length or 2 dips from the Big Dipper. The field of view is overhead at midnight in the middle of summer for those in the mid-Northern latitudes, and earlier in the evening in late summer and fall.

Galactic View

Our Sun is just one out of over 200 billion stars in our galaxy, the Milky Way. The Sun is located in the Orion arm of our galaxy about 75,000 light years from the center of the Galaxy. Kepler will be examining over 100,000 stars in our neighborhood of our galaxy in the Cygnus and Lyra constellations. Most of these stars will be somewhere between 500 and 3,000 light years from our solar system.

Lost in the Glare

Within our own solar system we can observe planetary transits of Mercury and Venus when they pass in front of the Sun as viewed from Earth. Kepler will observe the same phenomena in order to detect Earth-size planets, but from very far away. In fact, the distant suns that Kepler will observe are so far away that the stars are just points of light. Detecting an Earth-size planet transiting a distant star is like observing a gnat flying in front of a car’s headlight seen from many miles away.

Transit Graph

The results from Kepler will come from measuring the brightness of the stars. The data will look like an EKG showing the heart beat. Whenever a planet passes in front of its parent star as viewed from our solar system it produces a tiny pulse or beat. From the repeated beats we can detect and confirm the existence of Earth-size planets and learn about the orbit and size of the planet. The scientific results from Kepler come in a different way than most astronomy missions. It will not produce pretty pictures or even colorful spectrograms, but rather light curves that take several years to gather.

ComparativeLifeZones

The habitable zone is the distance from a star where one can have liquid water on the surface of a planet. If a planet is too close to its parent star, it will be too hot and water would have evaporated. If a planet is too far from a star it is too cold and water is frozen.
Stars come in a wide variety of sizes, masses and temperatures. Stars that are smaller, cooler and lower mass than the Sun (M-dwarfs) have their habitable zone much closer to the star than the Sun (G-dwarf). Stars that are larger, hotter and more massive than the Sun (A-dwarfs) have their habitable zone much farther out from the star.

Optical Path

Kepler does not directly observe the image of a planet. Rather it observes the effect the planet has on its parent star. If the orbit of the planet is aligned along Kepler's line of sight to the star, it will block a very tiny amount of light coming from the star to the Kepler telescope. The telescope will image the light from many stars at once. It uses 42 CCDs, charge coupled devices, detectors similar to those in commercial digital cameras, but much larger, having at total of 95 mega-pixels. With the CCDs Kepler is capable of observing over 100,000 stars all at once and measuring their brightness to an accuracy of better than 1 part in 100,000,  or ten parts per million. This is equivalent to looking at the Rose Bowl from the Goodyear blimp and detecting every time just one person walks in or out of the stadium.

Range Of Views

Kepler uses the transit method to detect the existence of a planet. A transit occurs when a planet passes in front of its parent star and blocks a bit of starlight while doing so.. The problem is that the orientations of planet orbits in other solar systems are randomly aligned. Some may even orbit face on. Only about 1% of the planets are aligned so that they can be detected by the transit method. Hence to detect a large number of planets we can't just look at a few stars. Hundreds or even a thousands stars are not enough. Rather, with Kepler, the scientists will be observing over 100,000 stars at once to find Earth size planets.

Zoology
Hot Jupiter
Earth-like World
Kuiper Belt World
Water World

Planets in our own solar system have a wide range of properties. They are distinguished by two basic properties, their size and their orbit. The size determines if the planet can have a life-sustaining atmosphere. The orbit affects the surface temperature and whether there could be liquid water on the planet's surface.

A habitable planet, one that could have liquid water on its surface must be between about 80% to 200% the diameter of Earth. Planets that are smaller then 8/10ths of an Earth diameter have less than half an Earth mass and do not have enough gravity to hold onto a life-sustaining atmosphere. Planets that are more than twice the diameter of Earth have about ten Earth masses and enough gravity to hold onto hydrogen, the most abundant element in the Universe. Such large planets turn into gas giants like Jupiter and Saturn. Jupiter is more than ten times the diameter of Earth and more than 300 times the mass of Earth.

Most of the 300 plus planets that have been detected so far are gas giants. The first extra-solar planet detected around a star similar to the Sun was 51 Peg. It has about the mass of Jupiter. But unlike Jupiter, which is five times as far from the Sun as Earth and orbits the Sun in 12 years, 51 Peg is twenty times closer to its star than Earth is to the Sun and orbits its star every 4 days. Planets like these are referred to as "Hot Jupiters.”
Kepler was designed specifically to detect Earth-size planets in the Habitable zone of solar-like stars. But it will also be capable of finding a range of planets as small as Mars in short period orbits to gas-giant planets, from burning hot to frozen worlds.

Launch sequence

These frames show the various phases of the Kepler launch sequence

Delta 2 on Launch pad at night

Kepler is NASA’s 10th Discovery mission. It is designed specifically to detect Earth-size planets orbiting in the habitable zone of solar-like stars. The telescope will stare continuously at over 100,000 stars in one region of the sky for 3 1/2 or more years looking for transits of planets, when they block a bit of light from their parent stars. From the amount of light blocked during the transit, scientists can calculate the size of the planet. Measuring the time between the transits , scientists can calculate the orbital period. Using Kepler’s Third Law of planetary motion, scientists then can calculate the distance the planet is from its star. The distance from the star largely determines the temperature of the planet and whether it may be habitable.

Kepler Launch at night

Kepler is launched at night (10:48 PM EST) on a Delta 2 expendable launch vehicle.

Fairing Separation

When the launch vehicle has risen sufficiently above the atmosphere, the fairings protecting the Kepler spacecraft during launch are jettisoned, exposing Kepler to space for the first time.

Second Stage

After a 43-minute coast in low Earth orbit, the second stage is fired for a final time.

Second Stage Separation

When the second stage burn is complete, the spacecraft and third stage are spun up to 55 rpm to stabilize the third stage during its short firing. The second stage is then jettisoned and the third stage is fired for a minute and a half.

Third Stage

Once the third stage finishes its work, Kepler will have sufficient energy to leave the gravitational pull of Earth and go into orbit around the Sun, trailing behind Earth and slowly drifting away from the Earth. Kepler and the Earth will pass each other every 61 years.