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2011 Science News: A Search for Habitable Planets

The planet-hunting space telescope Kepler has found 1,235 planet candidates

by Catherine McNiff

Kepler Telescope

Kepler focal plane assembly Source: NASA.

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The year 2011 proved to be a profitable one for the planet-hunting space telescope Kepler. As of February, our eye in the galaxy had found 1,235 planet candidates. The spacecraft is part of NASA's Kepler mission designed to uncover "Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets. Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy."

Kepler, named after Johannes Kepler, the father of the scientific method, employs transit timing variations (TTV) to determine the characteristics of a planet by measuring tiny decreases in the brightness of stars caused by planets crossing in front of them. How much or little a star dims determines the size of the planet. Similarly, how much time elapses between transits gives astronomers clues as to how long it takes for the planet to orbit around its star. Kepler must be patient as transits of planets in the habitable zone of sun-like stars are rare, occurring only about once a year (which means an Earth-like orbit of one year).

Not Riding Solo

The more planets transiting the same star, the more relative information the scientists can extract, including stability, gravitational interactions, planet masses, and orbital shapes. Until February 2011, there were only a few known stars with more than one orbiting planet. Enter Kepler 11, with an unheard-of six transiting planets. Located about 2,000 light years away, the extrasolar system is the most dense planetary arrangement that astronomers have ever seen and may help them understand the cosmos better and our place in it. The orbits of five of the planets range from 10 to 47 days, with the sixth planet enjoying a longer trip. The five inner planets are a few times larger than Earth and perform their galactic dance within an area smaller than the distance from the Sun to Mercury.

The discovery of this solar system marked a new era of planetary discovery, bringing the extraterrestrial home. The discovery of a twin-sunned planet affectionately nicknamed Tatooine after the similarly endowed planet in Star Wars in September sent a clear cosmic message—there is so much more out there to discover. A planetary scientist and Kepler science team member, Jack Lissauer, had this to say, "We suspected that the planetary zoo would have a great variety. But what that was, and how quickly we would find out about it, no way. This is way beyond anything we expected. Things like Kepler 11, these are just weird."

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