NASA’s Kepler Mission Discovers Bigger, Older Cousin to Earth
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This artist's concept compares Earth (left) to the new planet, called Kepler-452b,
which is about 60 percent larger in diameter.
Credits: NASA/JPL-Caltech/T. Pyle
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NASA's Kepler mission has confirmed the first near-Earth-size planet
in the “habitable zone” around a sun-like star. This discovery and the
introduction of 11 other new small habitable zone candidate planets mark
another milestone in the journey to finding another “Earth.”
The newly discovered Kepler-452b is the smallest planet to date
discovered orbiting in the habitable zone -- the area around a star
where liquid water could pool on the surface of an orbiting planet -- of
a G2-type star, like our sun. The confirmation of Kepler-452b brings
the total number of confirmed planets to 1,030.
"On the 20th anniversary year of the discovery that proved other suns
host planets, the Kepler exoplanet explorer has discovered a planet and
star which most closely resemble the Earth and our Sun," said John
Grunsfeld, associate administrator of NASA’s Science Mission Directorate
at the agency’s headquarters in Washington. “This exciting result
brings us one step closer to finding an Earth 2.0."
Kepler-452b is 60 percent larger in diameter than Earth and is
considered a super-Earth-size planet. While its mass and composition are
not yet determined, previous research suggests that planets the size of
Kepler-452b have a good chance of being rocky.
While Kepler-452b is larger than Earth, its 385-day orbit is only 5
percent longer. The planet is 5 percent farther from its parent star
Kepler-452 than Earth is from the Sun. Kepler-452 is 6 billion years
old, 1.5 billion years older than our sun, has the same temperature, and
is 20 percent brighter and has a diameter 10 percent larger.
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Of the 1,030 confirmed planets from Kepler, a dozen
are less than twice the size of Earth and reside in the habitable zone
of their host stars. In this diagram, the sizes of the exoplanets are
represented by the size of each sphere. These are arranged by size from
left to right, and by the type of star they orbit, from the M stars that
are significantly cooler and smaller than the sun, to the K stars that
are somewhat cooler and smaller than the sun, to the G stars that
include the sun. The sizes of the planets are enlarged by 25 times
compared to the stars. The Earth is shown for reference.
Credits: NASA/Ames/JPL-Caltech
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“We can think of Kepler-452b as an older, bigger cousin
to Earth, providing an opportunity to understand and reflect upon
Earth’s evolving environment," said Jon Jenkins, Kepler data analysis
lead at NASA's Ames Research Center in Moffett Field, California, who
led the team that discovered Kepler-452b. "It’s awe-inspiring to
consider that this planet has spent 6 billion years in the habitable
zone of its star; longer than Earth. That’s substantial opportunity for
life to arise, should all the necessary ingredients and conditions for
life exist on this planet.”
To help confirm the finding and better determine the properties of
the Kepler-452 system, the team conducted ground-based observations at
the University of Texas at Austin's McDonald Observatory, the Fred
Lawrence Whipple Observatory on Mt. Hopkins, Arizona, and the W. M. Keck
Observatory atop Mauna Kea in Hawaii. These measurements were key for
the researchers to confirm the planetary nature of Kepler-452b, to
refine the size and brightness of its host star and to better pin down
the size of the planet and its orbit.
The Kepler-452 system is located 1,400 light-years away in the
constellation Cygnus. The research paper reporting this finding has been
accepted for publication in The Astronomical Journal.
In addition to confirming Kepler-452b, the Kepler team has increased
the number of new exoplanet candidates by 521 from their analysis of
observations conducted from May 2009 to May 2013, raising the number of
planet candidates detected by the Kepler mission to 4,696. Candidates
require follow-up observations and analysis to verify they are actual
planets.
Twelve of the new planet candidates have diameters between one to two
times that of Earth, and orbit in their star's habitable zone. Of
these, nine orbit stars that are similar to our sun in size and
temperature.
“We've been able to fully automate our process of identifying planet
candidates, which means we can finally assess every transit signal in
the entire Kepler dataset quickly and uniformly,” said Jeff Coughlin,
Kepler scientist at the SETI Institute in Mountain View, California, who
led the analysis of a new candidate catalog. “This gives astronomers a
statistically sound population of planet candidates to accurately
determine the number of small, possibly rocky planets like Earth in our
Milky Way galaxy.”
These findings, presented in the seventh Kepler Candidate Catalog,
will be submitted for publication in the Astrophysical Journal. These
findings are derived from data publicly available on the NASA Exoplanet Archive.
Scientists now are producing the last catalog based on the original
Kepler mission’s four-year data set. The final analysis will be
conducted using sophisticated software that is increasingly sensitive to
the tiny telltale signatures of Earth-size planets.
Ames manages the Kepler and K2 missions for NASA’s Science Mission
Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California,
managed Kepler mission development. Ball
Aerospace & Technologies
Corporation operates the flight system with support from the Laboratory
for Atmospheric and Space Physics at the University of Colorado in
Boulder.
Finding Another Earth
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A newly discovered exoplanet, Kepler-452b, comes
the closest of any found so far to matching our Earth-sun system. This
artist’s conception of a planetary lineup shows habitable-zone planets
with similarities to Earth: from left, Kepler-22b, Kepler-69c, the just
announced Kepler-452b, Kepler-62f and Kepler-186f. Last in line is Earth
itself.
Credits: NASA/Ames/JPL-Caltech
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The discovery of a super-Earth-sized planet orbiting a sun-like star
brings us closer than ever to finding a twin of our own watery world.
But NASA’s Kepler space telescope has captured evidence of other
potentially habitable planets amid the sea of stars in the Milky Way
galaxy.
To take a brief tour of the more prominent contenders, it helps to
zero in on the “habitable zone” around their stars. This is the band of
congenial temperatures for planetary orbits -- not too close and not too
far. Too close and the planet is fried (we’re looking at you, Venus).
Too far and it’s in deep freeze. But settle comfortably into the
habitable zone, and your planet could have liquid water on its surface
-- just right. Goldilocks has never been more relevant. Scientists have,
in fact, taken to calling this water-friendly region the “Goldilocks
zone.”
The zone can be a wide band or a narrow one, and nearer the star or
farther, depending on the star’s size and energy output. For small,
red-dwarf stars, habitable zone planets might gather close, like
marshmallow-roasting campers around the fire. For gigantic, hot stars,
the band must retreat to a safer distance.
About a dozen habitable zone planets in the Earth-size ballpark have
been discovered so far -- that is, 10 to 15 planets between one-half and
twice the diameter of Earth, depending on how the habitable zone is
defined and allowing for uncertainties about some of the planetary
sizes.
The new discovery, Kepler-452b, fires the planet hunter’s imagination
because it is the most similar to the Earth-sun system found yet: a
planet at the right temperature within the habitable zone, and only
about one-and-a-half times the diameter of Earth, circling a star very
much like our own sun. The planet also has a good chance of being rocky,
like Earth, its discoverers say.
Kepler-452b is more similar to Earth than any system previously
discovered. And the timing is especially fitting: 2015 marks the 20th anniversary of the first exoplanet confirmed to be in orbit around a typical star.
But several other exoplanet discoveries came nearly as close in their similarity to Earth.
Before this, the planet Kepler-186f held the “most similar”
distinction (they get the common moniker, “Kepler,” because they were
discovered with the Kepler space telescope). About 500 light-years from
Earth, Kepler-186f is no more than 10 percent larger than Earth, and
sails through its star’s habitable zone, making its surface potentially
watery.
But its 130-day orbit carries it around a red-dwarf star that is much
cooler than our sun and only half its size. Thus, the planet is really
more like an “Earth cousin,” says Thomas Barclay of the Bay Area
Environmental Research Institute at NASA’s Ames Research Center, Moffett
Field, California, a co-author of the paper announcing the discovery in
April 2014.
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This artist's concept depicts one possible
appearance of the planet Kepler-452b, the first near-Earth-size world to
be found in the habitable zone of star that is similar to our sun.
Credits: NASA/JPL-Caltech/T. Pyle
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Kepler-186f gets about one-third the energy from its star that Earth
gets from our sun. And that puts it just at the outside edge of the
habitable zone. Scientists say that if you were standing on the planet
at noon, the light would look about as bright as it does on Earth an
hour before sunset.
That doesn’t mean the planet is bereft of life, although it doesn’t mean life exists there, either.
Before Kepler-186f, Kepler-62f was the exoplanet known to be most
similar to Earth. Like the new discovery, Kepler-62f is a “super Earth,”
about 40 percent larger than our home planet. But, like Kepler-186f,
its 267-day orbit also carries it around a star that is cooler and
smaller than the sun, some 1,200 light-years away in the constellation
Lyra. Still, Kepler-62f does reside in the habitable zone.
Kepler-62f’s discovery was announced in April 2013, about the same
time as Kepler-69c, another super Earth -- though one that is 70 percent
larger than our home planet. That’s the bad news; astronomers are
uncertain about the planet’s composition, or just when a “super Earth”
becomes so large that it diminishes the chance of finding life on its
surface. That also moves it farther than its competitors from the realm
of a potential Earth twin. The good news is that Kepler-69c lies in its
sun’s habitable zone, with a 242-day orbit reminiscent of our
charbroiled sister planet, Venus. Its star is also similar to ours in
size with about 80 percent of the sun’s luminosity. Its planetary system
is about 2,700 light-years away in the constellation Cygnus.
Kepler-22b also was hailed in its day as the most like Earth. It was
the first of the Kepler planets to be found within the habitable zone,
and it orbits a star much like our sun. But Kepler-22b is a sumo
wrestler among super Earths, about 2.4 times Earth’s size. And no one
knows if it is rocky, gaseous or liquid. The planet was detected almost
immediately after Kepler began making observations in 2009, and was
confirmed in 2011. This planet, which could have a cloudy atmosphere, is
600 light-years away, with a 290-day orbit not unlike Earth’s.
Not all the planets jostling to be most like Earth were discovered
using Kepler. A super Earth known as Gliese 667Cc also came to light in
2011, discovered by astronomers combing through data from the European
Southern Observatory’s 3.6-meter telescope in Chile. The planet, only 22
light-years away, has a mass at least 4.5 times that of Earth. It
orbits a red dwarf in the habitable zone, though closely enough -- with a
mere 28-day orbit -- to make the planet subject to intense flares that
could erupt periodically from the star’s surface. Still, its sun is
smaller and cooler than ours, and Gliese 667Cc’s orbital distance means
it probably receives around 90 percent of the energy we get from the
sun. That’s a point in favor of life, if the planet’s atmosphere is
something like ours. The planet’s true size and density remain unknown,
however, which means it could still turn out to be a gas planet, hostile
to life as we know it. And powerful magnetic fluxes also could mean
periodic drop-offs in the amount of energy reaching the planet, by as
much as 40 percent. These drop-offs could last for months, according to
scientists at the University of Oslo’s Institute of Theoretical
Astrophysics in Norway.
Deduct two points.
Too big, too uncertain, or circling the wrong kind of star: Shuffle
through the catalog of habitable zone planets, and the closest we can
come to Earth -- at least so far -- appears to be the new kid on the
interstellar block, Kepler-452b.
NASA's Ames Research Center in Moffett Field, California, manages the
Kepler and K2 missions for NASA's Science Mission Directorate. NASA's
Jet Propulsion Laboratory in Pasadena, California, managed Kepler
mission development. Ball Aerospace & Technologies Corp. operates
the flight system with support from the Laboratory for Atmospheric and
Space Physics at the University of Colorado in Boulder.
JPL is managed by The California Institute of Technology for NASA.
More information about NASA's planet-hunting efforts is online at:
http://planetquest.jpl.nasa.gov
A related news release about Kepler's latest planetary find is online at: http://www.nasa.gov/press-release/nasa-kepler-mission-discovers-bigger-older-cousin-to-earth
A related feature story about other potentially habitable planets is online at: http://www.nasa.gov/jpl/finding-another-earth
