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NASA's new mission to seek Earth-like planets
(02-19) 20:47 PST -- Somewhere far out in our Milky Way galaxy, thousands - perhaps millions - of pale blue dots are orbiting their suns just as Earth does ours, and in two weeks a new American spacecraft will fly off to seek them out.
Carrying a powerful telescope and one of the most sensitive cameras ever launched into space, the NASA ship named Kepler will hunt for terrestrial-size "exoplanets" whose orbits lie in what astronomers call the "habitable zones" of their distant solar systems.
The $591 million, 3 1/2-year mission, described today by NASA officials in Washington, is set to launch from Cape Canaveral on March 5, weather permitting.
"We hope to find hundreds of such planets," said space physicist William J. Borucki, who leads the mission's science team at the Ames Research Center in Mountain View.
Finding that many, he said, would increase the odds that life in some form or another exists and evolves on other planets throughout the Milky Way.
"If we don't find any, it will mean that a planet like Earth, with its life, must be very rare indeed, and so there will be no 'Star Trek,' " he said.
The spacecraft is not designed to seek out evidence of life itself - only to detect the existence of Earth-like planets in parts of their solar systems where life might be possible, Borucki said.
"Kepler is not designed to find E.T.," he said, "but it's hoping to find E.T.'s home."
Astronomers discovered the first known exoplanets in 1995, and since then more than 335 have been found. Most of them are "gas giants" larger and more massive than Jupiter; others known as "ice giants" are orbiting so far from their suns that they must be eternally frozen; and some known as "super-earths" - perhaps 10 times the mass of Earth - have gravity so powerful it would be hard to think of life existing on them.
Finding promising planets
Astronomer Debra Fischer of San Francisco State University, a pioneer in discovering exoplanets, said the Kepler flight will determine just how frequently Earth-size planets exist in habitable zones in the Milky Way. Fisher, who is not part of the mission team, said the venture is bound to be a "key driver" for future NASA spacecraft that will target specific planets to probe for evidence of some form of life. Specifically, the long-term goal would be to seek life-sustaining atmospheres and signs of liquid water - a crucial component of life.
"The 15- to 20-year vision of astronomers is a mission to take a picture of a pale blue dot orbiting a nearby star," Fischer said.
In Earth's trail
Although the mission, in development since 2001, is assigned to operate for 3 1/2 years, the spacecraft will carry enough fuel to operate its telescope and camera for at least six years, according to Jim Fanson, the project manager at NASA's Jet Propulsion Laboratory in Pasadena.
Kepler's orbit will trail Earth's path around the sun as it surveys more than 100,000 stars at distances ranging from 30 to 1,000 light-years in what is essentially a census-taking quest to count the number of Earth-like planets circling suns in orbits neither too close nor too far, too hot nor too cold, for life to exist.
The extraordinarily powerful camera, capable of imaging 100 million stars at once, is so sensitive that it can sense and measure the slight dimming of a target star's light as a planet passes in front it - an event known as a transit.
Faintest dimming
Fanson said it would be as if Kepler were to look down from space at a small town on Earth at night and its camera detected the dimming of a porch light as someone passed in front of it.
But as Borucki explained, Kepler must measure the faint dimming of a star's light during at least three successive transits of a planet - and also measure the planet's orbital distance from its star. Then the spacecraft can signal back to Earth that it has detected a planet the right size and on the right orbit to qualify as a potential candidate for future close-up investigation.
According to the astronomers on Kepler's scientific team, the mission will observe at least 100,000 stars in its first three years and could detect about 50 planets in "habitable zones" around those stars if most are roughly the size of Earth. Their calculations indicate that Kepler could detect about 150 such planets if most of them are at least one-third larger than Earth, and about 640 planets if most are more than twice the size of Earth.
That's only a rough estimate, and the number could vary from many more hundreds to zero, the astronomers concede.
