NASA Search for ExoPlanets, The Kepler Mission
Looking for Planets in the Habitable Zone
Aug 4, 2009
The search for extraterrestrial life has been on many people's minds for over a century. SETI (Search for Extraterrestrial Intelligence) is probably the most sustained search for radio signals from outer space that would provide evidence of Intelligent life beyond earthly confines. But that is only one way of looking for life. In March 2009, NASA launched a space probe that would look for earth-like planets, exoplanets, in the Milky Way galaxy. Exoplanets are planets outside of the solar system. NASA scientists Lawson and Traub have written for NASA about the exoplanet project and provide additional scientific details in "Earth-Like Exoplanets: The Science of NASA’s Navigator Program" (2006).
But essentially, the focus of the The Kepler mission involves looking for planets that are in the "field of life" also known as the habitable zone; such planets are close to a star, but not too close, or too far away. They are also similar in size to earth with the potential for an earth like atmosphere. The star also must be similar in size to the Sun.
Currently there are several earth-based telescopes that are being used in this project. The Keck Interferometer located in Hawaii is one, the large Binocular Telescope Interferometer which is a two 8-meter class telescope on Mount Graham, Arizona is another. Sim PlanetQuest at the Jet Propulsion laboratory and the Terrestrial Planet Finder observatory are NASA exoplanet study missions. The current search is limited to stars within 20 parsecs (60 light years). This is primarily due to the technology that is is currently in place but may change as technology changes. They are looking for the right combination of planet location, star size, and atmospheric components which allow water to exist and possibly life.
As described in the web page "Kepler", on NASA's Jet Propulsion Laboratory website, the quest of the Kepler mission is to find earth-size planets orbiting stars like our sun in the habitable zone. At this time the spacecraft is approaching 9 million miles from earth. It surveys a patch of stars. The spacecraft then remains focused on it for 30 days. It then moves on to a new star patch as programmed by the NASA team at the Ames Research center. The last download from Kepler occurred in June 2009 and it included a survey of 145,000 stars; this was 50 gigabits of data.
The Transit Method
So how does the spacecraft identify the planets? By the shadow. That is too simplistic, but when a planet passes in front of a star, it briefly hides part of the star from view. As it traverses the front of the star it leaves its transit mark. How fast and how big was the shadow. There is a dip in the brightness of the star, and this is a telltale mark. Once the planet is identified, the usual mathematical astronomic protocols are put in place: the size of the planet, its mass, its orbital velocity around the star and temperature are calculated.
The Kepler Telescope
The Kepler scope is a specially designed with a diameter of 0.95-meters. It is a photometer with a very large field of view, 105 sq degrees. By way of comparison, this is similar to the size of a person's hand held at arm's length. The mission life is expected to last about 3-4 years.
The Kepler Mission is one of several NASA exoplanet projects designed to look for evidence of earth-like planets with a habitable zone. This project is spaced based, but there are others earth bound. The quest is to look for planets that are close to a Sun-like star, but not too close or far away. As such, they present good physical and chemical opportunities for water and an atmosphere to be present on the planet and hence life.
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