'Transitory' Discoveries
The Sun will grow a tiny bit fainter this afternoon. Some of its light will be blocked by the planet Mercury, which is passing across the Sun as seen from Earth -- an event called a transit. Mercury is so tiny, though, that the dip in the Sun's brightness isn't enough to notice.
But astronomers can use transits to discover planets in other star systems. As a planet passes in front of its parent star, the star suddenly gets a little bit fainter. If the planet covers enough of the star, the dip in the star's light can be detected by telescopes on Earth. In fact, the technique has led to the discovery of about 10 possible planets.
A NASA spacecraft that's scheduled for launch in 2008 should do much better -- perhaps discovering hundreds of new planets. The craft is called Kepler. From outside Earth's obscuring atmosphere, it'll keep an eye on a hundred thousand stars, watching for small changes in brightness. If the changes occur at regular intervals, then they're probably caused by transiting planets.
Kepler should do much more than just find planets, though. It's designed to reveal how big the planets are -- including whether any are comparable to Earth -- and how far they are from their stars. And that will tell astronomers if any of the planets are at the right distance for liquid water -- the "sweet spot" for life.
You can find more about the Kepler mission on the web at kepler.nasa.gov.
Script by Damond Benningfield, Copyright 2006
For more about the Kepler Mission, visit NASA's website at http://kepler.nasa.gov.
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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