Sunday, July 26, 2009
New telescope looks for Earth-like planets
John Goss
John Goss is chairman of the Mid-East Region of the Astronomical League and a former president of the Roanoke Valley Astronomical Society.
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Blog
Mid-August nights are known by many skywatchers to be a time for the two-week-long Perseid meteor shower, which culminates in the morning hours of Aug. 12. This year, the waning gibbous moon interferes with viewing the dimmer meteor streaks, but don't let that stop you from enjoying the starry dome of a clear August night.
When people gather for casual meteor watching or stargazing, their thoughts and conversations invariably drift toward the possibility of life elsewhere in the galaxy. With all the stars above us, surely there must be life around one of them.
Astronomers wonder about that, too. Some of them are searching for Earth-like planets, and NASA is helping them. On March 6, an unusual mission began at Cape Canaveral, Fla., with the launch of the Kepler spacecraft.
Since 1992, astronomers have found more than 300 planets orbiting other stars. Those worlds have all been deemed too hostile for life because their surfaces are thought to be either baking hot or icy cold. Most have sizes that approach or exceed that of our solar system's largest planet, Jupiter. No planets have been found that even remotely resemble Earth. NASA's Kepler Mission may change that.
The spacecraft carries a telescope, the Kepler, that is much more sensitive than the Hubble Space Telescope for measuring slight changes in a star's light intensity, even though it is not nearly as large as the Hubble. Kepler will put that enhanced capability to good use for spotting a star's miniscule drop in brightness if one of its small, dark planets passes directly in front of it. For this to occur, the planet's orbital plane must intersect Kepler's line of sight. This technique is called the "transit method."
The Kepler telescope should detect light drops from transiting Earth-sized planets in one out of every 200 stars that have a similar diameter as our sun. To increase the chances for success, the telescope's design allows it to carefully examine the same 100,000 stars simultaneously every 30 minutes for more than three years. By the mission's conclusion, scientists hope to have found more than 200 Earth-sized worlds, and, presumably, some of them will orbit just at the right distances from their parent stars to have surface temperatures suitable for harboring life.
Where in the sky is Kepler pointed while it monitors those many thousands of stars for planetary transits?
This time of year in the early evening, the Summer Triangle stretches nearly overhead. Much of the area between its two most northerly stellar members, Vega and Deneb, lies in the field of view of Kepler's very wide eye. Other famous telescopes, including the Hubble, view a much smaller section, smaller than the sky area of the full moon.
With binoculars, scan between Vega and Deneb. Being just outside of the band of the Milky Way, this area is packed with hundreds of stars. While you are looking at them a few at a time, Kepler is watching all of them plus many more that you can't see. No matter how hard you try or how long you look, don't expect to see any stars dimming from passing planets. An Earth-sized body will block a scant 0.01 percent of the star's light, which is far too little for the human eye to discern.
Clear August evenings are perfect for looking at the Summer Triangle and wondering about life elsewhere. Look up and consider that there is a telescope helping find clues about this fantastic notion.
John Goss writes a monthly astronomy column for The Roanoke Times.
