Kepler finds first earth-size planets beyond
our solar system
20 December 2011
This chart compares the first Earth-size planets found
around a sun-like star to planets in our own solar
system, Earth and Venus. NASA's Kepler mission
discovered the new found planets, called Kepler-20e and
Kepler-20f. Kepler-20e is slightly smaller than Venus
with a radius .87 times that of Earth. Kepler-20f is a bit
larger than Earth at 1.03 times the radius of Earth.
Venus is very similar in size to Earth, with a radius of .95
times that our planet. Prior to this discovery, the smallest
known planet orbiting a sun-like star was Kepler-10b
with a radius of 1.42 that of Earth, which translates to 2.9
times the volume. Both Kepler-20e and Kepler-20f circle
in close to their star, called Kepler-20, with orbital
periods of 6.1 and 19.6 days, respectively. Astronomers
say the two little planets are rocky like Earth but with
scorching temperatures. There are three other larger,
likely gaseous planets also know to circle the same star,
known as Kepler-20b, Kepler-20c and Kepler-20d.
Image credit: NASA/Ames/JPL-Caltech
(PhysOrg.com) -- NASA's Kepler mission has
discovered the first Earth-size planets orbiting a
sun-like star outside our solar system. The planets,
called Kepler-20e and Kepler-20f, are too close to
their star to be in the so-called habitable zone
where liquid water could exist on a planet's
surface, but they are the smallest exoplanets ever
confirmed around a star like our sun.
The discovery marks the next important milestone in
the ultimate search for planets like Earth. The
new
planets
are thought to be rocky. Kepler-20e is
slightly smaller than Venus, measuring 0.87 times
the radius of Earth. Kepler-20f is slightly larger than
Earth, measuring 1.03 times its radius. Both planets
reside in a five-planet system called Kepler-20,
approximately 1,000 light-years away in the
constellation Lyra.
Kepler-20e orbits its
parent star
every 6.1 days and
Kepler-20f every 19.6 days. These short orbital
periods mean very hot, inhospitable worlds.
Kepler-20f, at 800 degrees Fahrenheit, is similar to
an average day on the
planet Mercury
. The surface
temperature of Kepler-20e, at more than 1,400
degrees Fahrenheit, would melt glass.
This artist's animation flies through the Kepler-20
star system, where NASA's Kepler mission
discovered the first Earth-size planets around a star
beyond our own. Animation credit:
NASA/Ames/JPL-Caltech
"The primary goal of the
Kepler mission
is to find
Earth-sized planets in the
habitable zone
," said
Francois Fressin of the Harvard-Smithsonian
Center for Astrophysics in Cambridge, Mass., lead
author of a new study published in the journal
Nature. "This discovery demonstrates for the first
time that Earth-size planets exist around other
stars
, and that we are able to detect them."
The Kepler-20 system
includes three other planets
that are larger than Earth but smaller than Neptune.
Kepler-20b, the closest planet, Kepler-20c, the third
planet, and Kepler-20d, the fifth planet, orbit their
star every 3.7, 10.9 and 77.6 days. All five planets
have orbits lying roughly within Mercury's orbit in
our solar system. The host star belongs to the
same G-type class as our sun, although it is slightly
smaller and cooler.
The system has an unexpected arrangement. In
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our solar system, small, rocky worlds orbit close to
the sun and large, gaseous worlds orbit farther out.
In comparison, the planets of Kepler-20 are
organized in alternating size: large, small, large,
small and large.
Kepler-20e is the smallest planet found to date orbiting a
Sun-like star. It circles its star every 6.1 days at a
distance of 4.7 million miles. At that distance, its
temperature is expected to be about 1,400 degrees F.
This is an artist's rendering. Credit: NASA/JPL-Caltech/T.
Pyle
"The Kepler data are showing us some planetary
systems have arrangements of planets very
different from that seen in our
solar system
," said
Jack Lissauer, planetary scientist and Kepler
science team member at NASA's Ames Research
Center in Moffett Field, Calif. "The analysis of
Kepler data continue to reveal new insights about
the diversity of planets and planetary systems
within our galaxy."
Scientists are not certain how the system evolved
but they do not think the planets formed in their
existing locations. They theorize the planets formed
farther from their star and then migrated inward,
likely through interactions with the disk of material
from which they originated. This allowed the worlds
to maintain their regular spacing despite alternating
sizes.
The Kepler space telescope detects planets and
planet candidates by measuring dips in the
brightness of more than 150,000 stars to search for
planets crossing in front, or transiting, their stars.
The Kepler science team requires at least three
transits to verify a signal as a planet.
The Kepler science team uses ground-based
telescopes and the Spitzer Space Telescope to
review observations on planet candidates the
spacecraft finds. The star field Kepler observes in
the constellations Cygnus and Lyra can be seen
only from ground-based observatories in spring
through early fall. The data from these other
observations help determine which candidates can
be validated as planets.
Kepler-20f orbits its star every 19.6
days at a distance of
10.3 million miles. Although its average temperature
could be as high as 800 degrees F, it might have been
able to retain a water atmosphere as it migrated closer to
the star after it formed. This is an artist's rendering.
Credit: NASA/JPL-Caltech/T. Pyle
To validate Kepler-20e and Kepler-20f,
astronomers used a computer program called
Blender, which runs simulations to help rule out
other astrophysical phenomena masquerading as a
planet.
On Dec. 5 the team announced the discovery of
Kepler-22b in the habitable zone of its parent star.
It is likely to be too large to have a rocky surface.
While Kepler-20e and Kepler-20f are Earth-size,
they are too close to their parent star to have
liquid
water
on the surface.
"In the cosmic game of hide and seek, finding
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planets
with just the right size and just the right
temperature seems only a matter of time," said
Natalie Batalha, Kepler deputy science team lead
and professor of astronomy and physics at San
Jose State University. "We are on the edge of our
seats knowing that Kepler's most anticipated
discoveries are still to come."
Provided by JPL/NASA
APA citation: Kepler finds first earth-size planets beyond our solar system (2011, December 20)
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