NASA's newest planet-hunting spacecraft Kepler is in good
shape to begin discovering Earth-like planets, according to its first science
results, released today.
The space telescope, launched
in March 2009, detected the giant extrasolar planet HAT-P-7b within its
first 10 days of taking data. Although this planet was previously discovered by
ground-based telescopes, the fact that Kepler found it and measured it in such
great detail bodes well.
Kepler is on
a quest to root out distant worlds that resemble our own Earth, and which
might be hospitable to life.
So far, the various Earth- and space-based planet-hunting
telescopes are only able to find worlds that are significantly larger and
hotter than our own, because they are easier to see. But Kepler was designed to
be capable of detecting a distant Earth-sized
planet in an Earth-like year-long orbit, which would give it roughly the
same temperature range as our home.
The preliminary results indicate the observatory is up and
running as expected.
"This tells us that Kepler has the photometric
precision necessary to see Earth-like planets," said Jon Jenkins, a Kepler
co-investigator at the SETI Institute in California. "Kepler's prospects
for detecting Earth-sized planets transiting Sun-like stars are good: The
instrument is performing much as expected."
Planet HAT-P-7b is nothing at all like Earth. This gas giant
world circles its star every 2.2 days in a tight orbit that heats up the
planet's surface to a boiling 4,310 degrees Fahrenheit (2,376 degrees Celsius).
"It is as hot as a glowing red heating element in your
stove or toaster," said David Koch, Kepler deputy principal investigator
at NASA Ames Research Center in California. "That means we can see light
from the planet itself."
As Kepler watched HAT-P-7b's host star, the telescope
observed a dip in the star's brightness as the planet passed in front of it in
what's called a transit, blocking some of the star's light. Kepler also noted a
smaller dip in light when the planet passed behind the star, because the
planet's small contribution to the total brightness was briefly shielded.
Previous observations of HAT-P-7b were not able to measure
this second, smaller effect, called an occultation.
"The depth of the signal from that occultation, that
tiny blocking of the light from the planet itself, is about the same as a
transit would be for a planet as small as Earth," Koch told SPACE.com.
"So we measured the same kind of signal as if we were detecting an Earth
by seeing this occultation."
That's good news for the Kepler team, although the
Earth-like discovery that scientists dream about will have to wait a while.
Since Kepler looks for transiting planets that produce very limited signals, at
least a few orbits must be completed before a signal is noticeable.
In the case of HAT-P-7b, this requires only a few days, but
for a truly Earth-like planet in an Earth-like 365-day orbit, about three years
will be necessary to discern a pattern.
Kepler was launched in March 2009 on a 3.5-year mission,
which scientists hope to extend if all goes well. The telescope is designed to
scan one portion of the sky, looking at about 100,000 stars simultaneously to
seek signs of planets temporarily obscuring their light. Astronomers hope the
mission will yield small terrestrial planets in what's called the habitable
zone, where a planet is not too far or too close to its star and its
temperature range is similar to Earth's and can host liquid water.
"Our mission is designed so that if Earths in
Earth-like orbits are common we expect to find as many as [roughly] 50 such
planets," Jenkins said.
If the mission is successful, humans could be a step closer
to finding alien life in the universe. No matter what it finds, the results
will be revealing. If Kepler completes its term without finding any Earth-like
planets, it could suggest that Earth, and life, are unique or at least special.
The Kepler team, led by principal investigator William
Borucki at NASA Ames, detailed Kepler's first results in a paper published in
the Aug. 7 issue of the journal Science.
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