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The Search for Another Earth
The Search for Another Earth
Exoplanets and the
Kepler Space Telescope
An exoplanet or extrasolar planet is
a planet that orbits a star other
than the Sun.
The first confirmation of an
exoplanet orbiting a mainsequence star was made in 1995,
when a giant planet was found in
orbit around the nearby star 51
Pegasi.
Some exoplanets have been imaged
directly by telescopes, but the vast
majority have been detected
through indirect methods such as
the transit method and the radialvelocity method.
The Search for Another Earth
Exoplanet Exploration
NASA's and ESA’s Exoplanet
Exploration Program represent
science and missions of
unprecedented scope and
ambition, promising insight into
humankind's most timeless
questions:
Where did we come from?
Are we alone?
The primary goal of these
explorations is to discover and
characterize planetary systems
and Earth-like planets.
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The Challenge
There are over 100 billion suns in
our own Milky Way galaxy to
search.
Exoplanets:
- Don't produce any light of their
own, except when young
- Are an enormous distance away
from us
- Are lost in the blinding glare of
their parent stars.
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The Challenge
Advances in data-gathering
technology and analysis
capabilities now provide
scientists with the advanced tools
and capabilities to enable this
exploration of our galaxy.
Observation from highly
specialized spacecraft supported
by ground-based telescopes has
become the primary method
used.
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The Kepler Spacecraft
Carrying a telescope specifically
designed for the search for
exoplanets, Kepler has been the
workhorse of this effort.
Kepler's goal is the creation of a
statistical survey that predicts how
many Earth-like planets likely exist
in our galaxy.
The spacecraft was launched into a
solar Earth-trailing orbit in March
2009.
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The Kepler Spacecraft
• Kepler is in a heliocentric or Suncentered orbit. This unusual
“Earth-trailing” orbit allows
Kepler continuous observation of
its target stars.
• Kepler’s region of study is in a
very star-rich part of our Milky
Way galaxy, far enough north of
the plane of Earth's orbit that
neither Earth nor the Sun will
encroach on Kepler's field of view.
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Where is Kepler looking?
Kepler is pointed in a region of the
sky near the constellations of
Cygnus and Lyra. The space
telescope constantly monitors over
150,000 stars watching for the
presence of an exoplanet passing in
front of a star.
Staring at these stars, Kepler’s
specialized instruments measure the
changes in light intensity over time
using the “transit method” of
detection.
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What is Kepler looking at?
Kepler is looking at the Cygnus
region along the Orion arm centered
on galactic coordinates:
76.32º,+13.5º or RA=19h 22m 40s,
Dec=+44º 30' 00'.
The star field is far enough from the
ecliptic plane so the Sun does not
shine into the telescope at anytime
during the year. This field of view
virtually eliminates any occultations
by asteroids and Kuiper-belt objects,
which commonly orbit near the
ecliptic plane.
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Transit Method of Planetary
Detection
If a planet passes directly
between a star and an observer's
line of sight, it blocks out a tiny
portion of the star's light, thus
reducing its apparent brightness.
Sensitive telescope
instrumentation can detect this
periodic dip in brightness.
Sensitive telescope
instrumentation can detect this
periodic dip in brightness. From
the period and depth of the
transits, the orbit and size of the
star’s planetary companions can
be calculated.
The Search for Another Earth
Transit Method of Planetary
Detection
If a planet passes directly between a
star and an observer's line of sight,
it blocks out a tiny portion of the
star's light, thus reducing its
apparent brightness. Sensitive
telescope instrumentation can
detect this periodic dip in
brightness.
Sensitive telescope instrumentation
can detect this periodic dip in
brightness. From the period and
depth of the transits, the orbit and
size of the star’s planetary
companions can be calculated.
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Confirming What Kepler Sees
The next step is to confirm the
findings.
One method used to confirm the
findings is to measure the
“wobble” of the star which tells
the extent of movement induced
by a planet's gravitational tug.
Another method is to measure
the “doppler shift” of the star’s
light frequencies as it moves
slightly with the exoplanet’s
orbit.
From these observations,
scientists can estimate the mass,
density and potential make-up of
the planet.
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Direct Methods of Detecting
Exoplanets
Specialized optics and
observation methods have made
some exoplanet images possible.
These images from the Palomar
Observatory in California show an
array of planets around the star
HR 8799.
The light from the central star is
blackened to reveal its planets.
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Kepler’s Results
This diagram shows locations of
Kepler planet candidates in the
Kepler full field image.
The number of candidates in
Kepler data now totals 4,696
potential planets orbiting 4,743
stars. There are 1935 confirmed
planets as of January 2016.
The Kepler Mission assesses each
candidate with its "Follow-up
Observing Program" designed to
distinguish true planets from the
imposters.
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Orrery of Planet Candidates
A visualization of all the multipleplanet systems discovered by the
Kepler spacecraft as of February
2012.
The orbit radii are to scale with
respect to each other and planet
sizes are to scale with respect to
each other, but orbits and planet
sizes are different scales.
The colors are in order of semimajor axis: two-planet systems
(242 in all) have a yellow outer
planet; 3-planet (85) green, 4planet (25) light blue, 5-planet (8)
dark blue, 6-planet (1, Kepler-11)
purple.
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TheHabitable Zone
Kepler is seeking evidence of
Earth-size planets in the habitable
zone of Sun-like stars. The bigger
challenge is to find planets in the
habitable zone of their stars
where liquid water and possibly
life might exist.
To date, Kepler has confirmed 297
planet candidates in the habitable
zone.
It appears that some of these
planets have water present.
The Search for Another Earth
TheHabitable Zone
Kepler is seeking evidence of
Earth-size planets in the habitable
zone of Sun-like stars. The bigger
challenge is to find planets in the
habitable zone of their stars
where liquid water and possibly
life might exist.
To date, Kepler has confirmed 297
planet candidates in the habitable
zone.
It appears that some of these
planets have water present.
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What’s Next for Kepler?
The loss of two reaction wheels
on the Kepler spacecraft in 2013
brought an end to Kepler's
primary mission. In June 2014,
the K2 mission was established
which enables continued
observations with Kepler.
K2 is a community-driven mission
which entails observing
“campaigns” of fields distributed
around the ecliptic plane.
Kepler is expected to continue
operating until 2017 or 2018.
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Continued and Future Research
Spacecraft Operations into the
future:
--Continued operation of Kepler,
Hubble and Spitzer Space
Telescopes
--Operation by ESA’s Gaia satellite
--Launch of ESA’s CHaracterizing
ExOPlanet Satellite (CHEOPS)
--Launch of NASA’s Transiting
Exoplanet Survey Satellite in 2017
--Launch of NASA’s James Webb
Space Telescope in 2018.
GAIA
Spacecraft
The Search for Another Earth
For more information regarding the search for exoplanets
• NASA Planet Quest: The Search for Another Earth
http://planetquest.jpl.nasa.gov/
• NASA Exoplanet Exploration Program
http://exep.jpl.nasa.gov/
• Exoplanet Science Institute
http://nexsci.caltech.edu/
• ESA Gaia
http://www.esa.int/Our_Activities/Space_Science/Gaia
The Search for Another Earth