Kepler: Finding Earth-Size and Smaller Extrasolar Planets

Tonight, March 6, a Delta II rocket lifted off from the launch pad at NASA's Cape Canaveral Air Force Station in Florida, United States. Onboard is a very special payload, Kepler. Kepler's mission is to try to reach the ages old goal of trying to find something somewhere else in the universe like us. Right now, we know about many extrasolar planets, planets outside our solar system, but most of these are gas giants or very hot planets. What we want to find more of, however, is planets like our own Earth. We are seeking terrestrial planets, about one-half to twice the size of the Earth, located at an ideal distance away from the star so that liquid water can exist on the surface of the planet. And the Kepler Instrument is made specifically to tackle this monumental challenge. Its challenge is to survey our region of the Milky Way galaxy (right) to search for exactly these planets, and find out how common they are in our galaxy.

Transit Method

Kepler utilizes the transit method to extract information about a specific planet. During a transit, when a planet passes in front of its star as appearing on Earth, there is a tiny drop in brightness. Kepler uses this to find planets. It can then calculate the orbital size from the period of the planet (the amount of time it takes to orbit the star) and the mass of the star, by using Kepler's Third Law of planetary motion.

The amount of brightness a star drops by during the transit, called the depth of the transit, can give additional information. Since the size of the star is known, the planet's size can then be found by using its orbital size and the temperature of the star.

All of this information is not merely trivia. These can tell a lot about a planet, and ultimately give a strong indicator about whether or not the planet is able to support life as we know it. And this process is carried out for thousands of stars throughout the mission. All of these tasks may seem hard for just one telescope, but Kepler is completely prepared.

The Kepler Instrument

The Kepler Instrument (left) is built to confront the numerous jobs given to it. It is a 0.95-meter (about 3 feet) diameter telescope called a photometer or light meter. This telescope has a large field of view, 105 square degrees, meaning it is able to view a large portion of the sky at once (right). The Kepler Instrument will continuously analyze this same field and simultaneously handle the brightness of 100,000+ stars throughout the entire 3.5 year mission. Since the telescope is in space, it can avoid the loss of precision, that can happen easily on Earth, necessary to conduct this important research.

The Kepler Mission may lead us to find out many planets very similar to ours, and will help get us closer
to finding the answer to where life may exist in the universe.

Images: NASA


Astronomy and Space celebrates International Year of Astronomy 2009.