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By Lisa M. Krieger
[email protected]
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Our world felt a little less special on Monday, as
NASA's Kepler mission announced the discovery of an "earth-sized"
planet orbiting a "sun-like" star.
Yes, another one.
But this new orb merits special status -- because it's the first
planet to be officially confirmed to exist in the so-called
"habitable zone." It's an ideal size. It orbits just the right
distance from its star. And its star is a lot like our own sun.
This means that the planet, called Kepler-22b, is the best bet
yet to be a place with a thick atmosphere and a wet landscape.
The discovery "is a major milestone on the road to finding
Earth's twin," said Douglas Hudgins, Kepler program scientist at
NASA Headquarters in Washington, visiting Moffet Field's NASA Ames
for the five-day First Kepler Science Conference.
If this all sounds a little familiar, it's because we're getting
better and better at finding things.
Twice before astronomers have announced near-Earth-size planets
in habitable zones, although clear confirmation has proved
elusive.
The tally of confirmed and "candidate" planets grows every day.
Just a year and a half into Kepler's planet-hunting mission, there
are 28 confirmed planets and 2,326 candidate planets -- of which a
stunning 1,000 have been found since February.
Of the 54 candidate planets in the "habitable" zone, where
liquid water could exist, Kepler-22b is the first to be confirmed.
This milestone will be published in The Astrophysical Journal.
Earth-like candidates
The powerful telescopes are finding other things, too.
In another big announcement on Monday, using telescopes at the
Hawaii-based Keck Observatory and the McDonald Observatory in
Texas, astronomers at UC-Berkeley announced the discovery of the
largest black holes to date -- two monsters with masses equivalent
to 10 billion suns that are capable of consuming anything, even
light, within a region five times the size of our solar system.
The $600 million Kepler spacecraft peers at about 150,000 stars
in the constellations Cygnus and Lyra, trying to detect any change
in star brightness that suggests a passing planet. Three dips, or
dimming, must be seen for confirmation.
The Kepler science team uses ground-based telescopes and the
Spitzer Space Telescope to review observations on planet candidates
that the spacecraft finds, validating their identify.
"The tremendous growth in the number of Earth-size candidates
tells us that we're honing in on the planets Kepler was designed to
detect: those that are not only Earth-size, but also are
potentially habitable," said Natalie Batalha, Kepler deputy science
team lead at San Jose State University.
"The more data we collect, the keener our eye for finding the
smallest planets out at longer orbital periods," she said.
The planet, named Kepler-22b, is 2.4 times wider than Earth.
But the true nature of the new planet remains a mystery. No one
knows whether it's rocky, gaseous or liquid.
If it has a surface, astronomers estimate temperatures in the
comfy 70-degree range -- T shirt weather.
To better understand the Kepler 22-b's composition, it is first
necessary to measure its density and mass -- that is, how heavy it
is. The Kepler telescope can't do this, but Keck and other
ground-based telescopes can. Scientists hope to try this next
summer.
And we don't yet have the tools to detect far-away signs of
metabolism, with biological markers like atmospheric oxygen or
methane.
But any notion of earthlings settling down on Kepler 22-b has
one highly significant challenge: distance. The space shuttle,
heading out today at 17,000 mph, would reach our nearest star
system -- Alpha Centauri, slightly more than four light years away
-- in about 165,000 years. The new planet is 600 light years away
-- so that same shuttle would get there in 23 million years.
SETI tunes in
But Kepler-22b seems to several intriguing similarities
with Earth. Its home star, some 600 light years away, is "almost a
solar twin," Batahla said. So the light hitting the planet's
surface would be almost the same color as the light that
illuminates Earth.
And Kepler-22b's year is almost the same length as an Earth
year: 290 days instead of 365.
It is a prime target for the Search for Extra-Terrestrial
Intelligence (SETI), carried out with the dedicated 42-dish Allen
Telescope Array in Northern California, said Jill Tarter of
Mountain View's SETI Institute.
A preliminary search for radio signals from Kepler-22b is
already underway, she said. There are billions of radio channels to
be examined.
Discovering all these new planets sounds impressive -- but it's
only a prologue to a far larger story, according to SETI
Institute's Seth Shostak, in response to Monday's news.
"Extrapolating the results from searches, it's safe to say that
the vast majority of stars are ringed by planets," he wrote.
"Indeed, the best guess is that the tally of planets in our own
galaxy is approximately a trillion."
"It's reasonable to imagine," according to Shostak, "that
Kepler-22b has a billion siblings in our galaxy: a billion other
Earth-like worlds threading the vast tracts of the Milky Way."
Contact Lisa M. Krieger at 408-920-5565.
Kepler discoveries
- 1 confirmed planet in "habitable" zone, where liquid
water could exist
- 28 confirmed planets
- 54 unconfirmed planets in "habitable" zone
- 2,326 unconfirmed planets. Of these, 207 are approximately
Earth-size, 680 are super Earth-size, 1,181 are Neptune-size, 203
are Jupiter-size and 55 are larger than Jupiter.
