Image: Kepler's mirror
NASA/Ball Aerospace
A technician inspects Kepler's lightweight, honeycomb-like primary mirror, which weighs only 14 percent that of a solid mirror of the same dimensions and is made out of ultra-low expansion glass.
updated 3/4/2009 3:05:12 PM ET 2009-03-04T20:05:12

NASA's sharp-shooting Kepler spacecraft is ready to take its place this week in the pantheon of planetary detection technologies.

It wasn't long ago when a question mark loomed over astronomers pondering whether other planetsexisted beyond our little family of solar system worlds. Today, nearly 330 exoplanets have been discovered in the past 15 years — most of which are gas giants with characteristics similar to Jupiter and Neptune.

It's a little out of the astronomical limelight, but there are those that see planet hunting as a "space race" ... a worldwide competition to find other Earths circling their respective stars.

In early February, it was announced that the French Convection Rotation and Planetary Transits spacecraft had discovered the smallest exoplanet yet, and with a surface to walk on to boot, albeit blazingly boot-melting hot.

COROT-exo-7b is the tiniest terrestrial planet ever detected outside the Solar System and orbits a sun-like star.

"CoRoT is an excellent mission...a complimentary mission to Kepler," explained William Borucki, Kepler's science principal investigator at NASA's Ames Research Center at Moffett Field, Calif.

Those using CoRoT have found that many of the stars they've surveyed are more variable than expected, Borucki noted in a February 19 NASA press briefing on Kepler.

"So it's going to be harder for us to find some of these planets. That's one of the reasons they haven't found as many planets as they had hoped for at this time," Borucki said. Still, the CoRoT team remained confident that their spacecraft will find many more planets, he added.

Show time for Kepler
Now it's show time for NASA's Kepler, which is set for a late-night liftoff on Friday, March 6.

It is billed as the first mission with the ability to find planets like Earth — rocky planets that orbit sun-like stars in a warm and cozy zone where liquid water could be sustained on the surface. Liquid water is viewed as crucial for the formation of life.

"The CoRoT mission continues to provide surprises with its latest discovery of a hot super Earth with a 21-hour orbit. The Kepler mission looks forward to the challenge of being the first to find an Earth-size planet in the habitable zone of another star," Borucki advised

There are a host of differences between the two spacecraft.

The CoRoT mission, along with its planet finding skills, is also designed to detect the subtle variation in a star's light, caused by sound waves rippling across the surface. By doing this, CoRoT will gain a detailed insight into the internal conditions of the star. This technique is known as asteroseismology.

Slideshow: Month in Space: January 2014

For the $600 million Kepler, there is one goal: finding Earth-size planets in the habitable zone of sun-like stars.

CoRoT launched in December 2006 and in the last two years has led to the discovery of six giant planets and the recent claim of a terrestrial planet in a 21-hour orbit with a diameter about 1.7 times that of the Earth.

More discoveries of hot terrestrial size planets larger than the Earth are expected in the coming years. However, because of CoRoT's small aperture and because it can only look at a star field for five months before turning to another, it is not expected to discover Earth-size planets in the habitable zone.

Kepler, meanwhile, is specifically designed to discover dozens of Earth-size planets in the habitable zone and hundreds near the habitable zone.

A comparison of Kepler to CoRoT shows that Kepler has a 95-centimeter aperture, a field of view of 100 square degrees, 42 detectors, and monitors a field of view long enough to find planets with periods as long as 1.5 years.

For CoRoT, it has a 27-centimeter aperture, a field of view of four square degrees, and two detectors for planet finding, and monitors a single field of view long enough to find planets with periods no longer than 2.5 months.

Strong hints
At the ready to dive in on Kepler's findings is James Kasting, a professor of geosciences at Pennsylvania State University in State College, Pa. One of his space specialties is assessing habitable zones around stars and the search for extraterrestrial life.

"I'm thrilled that Kepler is about to launch," Kasting told

Kasting spotlighted CoRoT's recent finding of a super-Earth — about two Earth diameters — circling a sun-like star and having a surface temperature in excess of 1,500 degrees Celsius (2,700 degrees Fahrenheit).

"Kepler, if it works, should find Earth-mass planets orbiting at one Astronomical Unit around sun-like stars ... assuming, of course, that they are present," Kasting said. "As such it will give us strong hints as to whether other habitable planets exist."

Looking beyond Kepler and CoRoT, Kasting said what's really needed is a combination of space-based astrometry and space-based direct imaging to find Earth-sized planets around nearby stars and to study them spectroscopically.

"A positive result from Kepler could help give us the momentum to get those missions funded," Kasting suggested.

Statistically valid estimate
The French CoRoT spacecraft is serving largely to whet our appetite for what Kepler will discover, said Alan Boss in the Department of Terrestrial Magnetism at the Carnegie Institution of Washington in Washington, D.C.

Boss is the author of the newly published "The Crowded UniverseThe Search for Living Planets" a book that points out that a "new space race" is under way. The winner will claim victory, he writes, by discovering how frequently Earth-like planets occur in our neighborhood of the Milky Way Galaxy.

Boss pointed out that the CoRoT spacecraft sports a smaller diameter (less than one-third of Kepler), a smaller field of view for transit searches (about 20 times smaller than Kepler's),  and has a restriction to staring for no more than 150 days at the same stars versus at least 3.5 years for Kepler.

All that adds up to key facts: "CoRoT is able to find a few hot and warm super-Earths, but not the habitable Earths that Kepler will discover," Boss told "Kepler should also discover enough Earth-like worlds — probably dozens — to yield a good, statistically valid estimate of the frequency of Earths," he said.

"CoRoT is wonderful," Boss concluded, "but Kepler will be 'wonderfuller!'"

High hopes
Meanwhile, hopes are high for Kepler here at the Boulder, Colorado-based Ball Aerospace & Technologies Corporation. Ball is the firm responsible for developing the planet-hunting Kepler flight system and is supporting mission operations.

Working closely with Ball in operating the spacecraft is a team of 20 students and 16 professionals from the neighboring University of Colorado, Boulder's Laboratory for Atmospheric and Space Physics.

There were 1,350,000 labor hours here at Ball, in-house, to build that machine," said John Troeltzsch, Ball Aerospace Program Manager for Civil Space Systems. "Kepler is a very unique NASA telescope in that we have a huge field of view," he told

Troeltzsch said that Kepler is "perfectly optimized" to search for Earth-size planets in the habitable zone of their parent stars.

While Kepler is on tap for a three-and-a-half year prime mission, the hope is for extending its planet-searching duties.

"The longer you go ... the more science you're going to get," Troeltzsch said. "We get up there and we're finding planets, there's really going to be, I think, a lot of compelling reasons to extend the mission."

Predicted Troeltzsch: "I think we're going to find a lot of planets. It's going to change the way people think about space. And I also think it's going to change the way NASA's targeting future missions to do follow-up."

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