NASA’S Kepler mission
By detecting tiny changes in brightness, telescope will seek planets comparable to our own
By MARK CARREAU
Copyright 2009 Houston Chronicle
March 2, 2009, 7:12AM

The universe may be filled with Earth-like planets — worlds where extraterrestrials might flourish.

But these planets were once considered too small to spot, even with the latest in space technology.

Now, many astronomers believe NASA’s $600 million Kepler telescope, which is scheduled to shoot into space this week, will help to clear up the mystery.

Named for Johannes Kepler, a 17th-century German astronomer who studied planetary motion, the telescope is designed to search 100,000 stars in the Milky Way for Earth-sized rocky planets where water could flow and form streams, lakes and oceans.

Some astronomers believe the spacecraft could eventually find about 50 Earth-like planets.

“If we find that many, it will certainly mean life may well be common throughout our galaxy,” said William Borucki of NASA’s Ames Research Center, the astronomer who leads the Kepler science team.

“On the other hand, if we don’t find any, that is still a profound discovery,” he said. “It will mean that Earth must be very rare. We may be the only life in our universe.

“It will mean there will be no Star Trek.”
Finding wobbly stars

The unmanned Kepler is scheduled to lift off aboard a Delta II rocket on Friday from the Cape Canaveral Air Force Station in Florida.

Its quest, though, is not as fanciful as it may seem.

Astronomers first discovered a planet outside our solar system in 1994 and have since identified 340 of them.

But even the best observatories, the Hubble Space Telescope among them, are not equipped to spot something as tiny as the Earth at great distances.

So far, the discoveries have been made with telescopes that detect small wobbles in the movement of stars, which astronomers attribute to the gravitational tug of unseen planets.

Most of these worlds rival giant Jupiter in size. Many are larger. Some circle their stars so closely that their surface temperatures are much too high for life.

Last month, French scientists announced the discovery of Exo-7b, the second planet circling the Exo-7 star about 390 light years away.

Though twice as large as the Earth, Exo-7b is the closest match to our planet yet found. Exo-7b, however, orbits so close to its sun that the planet’s surface temperatures hover around 1,800 degrees Fahrenheit.

Experts say their best guess is that Exo-7b is covered in molten lava or is a steamy world that is half rock, half water vapor.

The planet was discovered by the Corot, an Earth-orbiting telescope that France launched six years ago.

NASA’s larger Kepler spacecraft promises to do better.

The telescope has a field of view 20 times larger than Corot’s, and it’s designed to circle the sun on a course that trails the Earth. The path permits the telescope to aim at the constellations Cygnus and Lyra, a field of view that will not be blocked by our sun or moon.
Measuring light

Kepler, essentially a large light meter, does not photograph stars. It was designed to detect small changes in the brightness of a distant star when a planet as small as Mars makes a crossing, or transit.

Kepler’s sensitivity is remarkable. It has the power to detect a dip in illumination as slight as one caused when a mosquito buzzes in front of a car’s headlight.

The spacecraft’s field of view is large enough to view 100,000 stars — just a small number in the entire galaxy — all the time.

By measuring the changes in illumination of the stars, ranging from 30 to 10,000 light years away, astronomers can calculate the masses of their planets and the frequency of their passage, factors that indicate how closely they resemble the Earth.

“Kepler,” said Jon Morse, NASA’s top astrophysicist, “will push back the boundaries of the unknown in our patch of the Milky Way galaxy.

“And its findings may fundamentally alter humanity’s view of itself.”