SAN JOSE, Calif. — 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 in California 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.
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 the
University of California, 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 identity.
“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.
But Kepler-22b seems to
have 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 under
way, 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.”
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©2011 the San Jose Mercury News (San Jose, Calif.)
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