Kepler blasts off in search of Earth-like planets
The $590-million mission, jointly managed by JPL and NASA, will examine a star-rich stretch of sky for a planet where water could exist in liquid form
March 7, 2009, Source:
Los Angeles Times by John Johnson Jr.
NASA's Kepler spacecraft blasted off from Kennedy Space
Center in Florida on Friday on a three-year mission to
find Earth's twin, a Goldilocks planet where it's
neither too hot nor too cold, but just right for life to
take hold.
The Delta II rocket, carrying the widest-field telescope
ever put in space, lifted off the launch pad at Cape
Canaveral at 10:49 p.m. Eastern time.
The launch vehicle headed downrange, gathering speed as
its three stages ignited, one after the other, passing
over the Caribbean island of Antigua and tracking
stations in Australia before climbing into orbit.
Kepler will eventually settle down to scan tens of
thousands of stars near the constellations Cygnus and
Lyra in search of planets where water could exist on the
surface in liquid form, a key condition for life as we
know it.
"We have a feeling like we're about to set sail across
an ocean to discover a new world," said project manager
Jim Fanson of the Jet Propulsion Laboratory in La Caņada
Flintridge. "It's sort of the same feeling Columbus or
Magellan must have had."
The $590-million Kepler mission is jointly managed by
JPL and NASA's Ames Research Center in the Bay Area. The
spacecraft carries a 15-foot-long telescope with a
55-inch mirror that can scrutinize a wide star field for
the telltale dimming of starlight that occurs when a
planet crosses in front of it, known as a transit.
Over the last decade, scientists have employed the same
technique with ground-based telescopes to discover 340
planets circling other stars. But because the optics of
ground-based instruments are compromised by atmospheric
interference, most of the planets found so far are
Jupiter-like gas giants that orbit so close to their
parent stars that any life forms would be incinerated.
The orbiting Hubble Space Telescope, whose optics are
not hampered by Earth's atmosphere, was designed to see
deeply but very narrowly.
Credit: Malcolm Denemark / Associated Press
Kepler's field of view is 33,000 times wider than
Hubble's, or about the size of a human hand held up to
the sky. The Cygnus-Lyra region near the plane of the
Milky Way encompasses about 4.5 million stars. But most
of those are too big or hot to allow a habitable zone
close enough to the star for Kepler to see a transit.
The science team has selected about 150,000 sun-like
stars for Kepler to analyze. Over time, Fanson said, the
number will be winnowed down to about 100,000 in three
classes: G-type stars, which are similar in size and age
to the sun; K- and M-type stars, which are slightly
smaller and cooler; and A- and F-class stars, which are
somewhat bigger.
Earth is in the center of the habitable zone around the
sun, but with stars of other classes, that zone would be
closer to the star or farther out.
Kepler's telescope is outfitted with a sophisticated
camera that will stare unblinkingly at the star field.
The whole area will be imaged every six seconds, then
stored in 30-minute chunks.
Once a month, Kepler will do a pirouette in space to
download its stored data, Fanson said.
The scientists expect to find hundreds of planets during
the mission, scheduled to last more than three years.
But even with the telescope's wide field of vision, it
will be no easy task for Kepler to find smaller,
Earth-like planets. Scientists have calculated that the
change in brightness caused by such a planet transiting
its star will be only about 0.008%, or about 84 parts
per million. On top of that, there is less than one
chance in 100 that a planet circling a far-off star will
be aligned in just the right way for Kepler to spot a
transit.
A final complication is that not all dimming is caused
by transits. Sunspots on the surface of a star are
cooler areas linked to an increase in magnetic activity.
They also cause the star's light to dim. But Kepler
scientists said they think they understand the signature
of sunspots well enough to deal with that problem.
For a planet to become a candidate for the first
Earth-type planet around another star, Kepler must
measure at least three separate transits, scientists
said. If the team is uncertain about some measurements,
or simply wants more observing time, the mission could
be extended to six years, NASA said.
NASA's greatest science missions
1. Apollo 11: the first manned mission to land on the Moon.
2. Hubble Space Telescope.
3. Viking: Mission to Mars.
4. Chandra: Exploring the Invisible Universe: Chandra X-ray Observatory.
5. Cassini-Huygens: Mission to Saturn and Titan.
6. Spirit & Opportunity: NASA's Mars Exploration Rover.
7. Spitzer: Space Telescope infrared light
8. WMAP, the Wilkinson Microwave Anisotropy Probe.
9. Voyager: exploration of Jupiter and Saturn.
10. Pioneer: the first spacecraft to visit Jupiter and Saturn.
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