Transcript Extrasolar Planets

The Search For
Extrasolar Planets
Ever since humans first gazed into the
night sky, the question of whether we
are alone in the universe has
remained unanswered.
The Search For
Extrasolar Planets
Recent
technological
advances allow
astronomers to
address this
question by
searching for
planets beyond
our solar system.
The Search For
Extrasolar Planets
Astronomers use several techniques
to search for extrasolar planets:
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Direct Detection
Transit
Astrometry
Doppler Spectroscopy
Detection of
Circumstellar Disks
The Search For
Extrasolar Planets
Direct Detection:
The most
obvious way to
find a planet
outside our
solar system is
to see it through
a telescope.
Right?
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Extrasolar Planets
Wrong.
The light of a star is 1 million to 10 billion
times brighter than the light reflected by a
planet, making it nearly impossible to see
the planet. It’s like trying to see a firefly in
front of a search light.
The Search For
Extrasolar Planets
Since technology
doesn’t yet allow
astronomers to
directly detect
extrasolar
planets, they look
for the indirect
effects of planets
on their parent
stars.
The Search For
Extrasolar Planets
Transit:
Astronomers can measure the decrease in
apparent brightness of a star as a planet
eclipses (or transits) it.
The Search For
Extrasolar Planets
In 2001, Hubble
detected the
atmosphere around
an extrasolar planet.
The planet itself was
not directly visible.
Instead, sodium was
detected in light
filtered through the
planet's atmosphere
when it transited its
star, HD 209458.
Artist’s conception of a gas-giant
planet orbiting star HD 209458.
The Search For
Extrasolar Planets
In 2003, the planet
OGLE-TR-56b was
detected using the
transit method. Based
on a 1% dimming in the
star's brightness during
transit, astronomers
believe the planet is
about the size of
Jupiter.
Artist’s conception of OGLE-TR-56b
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Extrasolar Planets
Transit is a limited detection method, since only
planets with side-on orbits will obscure our
view of their stars. HD 209458 was first detected
not by transit, but by measuring its gravitational
pull on the parent star, called “wobble.”
The Search For
Extrasolar Planets
Astrometry:
• Bodies orbiting a star
cause it to ‘wobble’
around the system’s
center of mass.
• Precise measurement
of this change in a
star’s position
(“astrometry”) may
allow astronomers to
detect a planet.
If alien astronomers 33 light-years
away tracked the motion of our Sun
relative to the center of mass of the
solar system (CMSS), they would
observe a measurable ‘wobble’
caused by planets in orbit. The
green sphere shows the actual size
of the Sun.
The Search For
Extrasolar Planets
A planet was discovered around star G1876 using
astrometry. G1876 is close to Earth (15 light-years),
and the planet is half its size, exaggerating the
wobble. Few stars are close enough to be detected
by this technique.
The Search For
Extrasolar Planets
Doppler Spectroscopy:
Most detections thus far have been achieved by the
radial-velocity technique from ground-based
telescopes, in which a star’s wobble is measured as
a shift in the frequency of light emitted by the star.
When the star moves
toward Earth, we see a
shift toward the blue
end of the spectrum.
When the star moves away
from us, the light shifts to
the red end of the spectrum.
The Search For
Extrasolar Planets
Over 100 extrasolar planets
have been detected using
Doppler Spectroscopy. Most
are close to their parent
stars and several times
more massive than Jupiter.
This technique cannot
detect smaller worlds. With
the best spectroscopes,
astronomers can detect
motions of about 15
meters/second. Earth only
forces the Sun to move at
0.1 meters/second.
Artist’s conception
of a giant planet
close to its sun.
The Search For
Extrasolar Planets
This chart compares sizes and orbits of known
extrasolar planets to our own solar system.
The Search For
Extrasolar Planets
Detection of Circumstellar Disks:
We also get clues
about other
planetary systems
by looking for
dust disks around
stars. Disks may
indicate locations
where planets are
forming or have
already formed.
Infrared image of Beta Pictoris.
The presence of a warp in this
disk indicates the existence of a
Jupiter-sized planet.
The Search For
Extrasolar Planets
Irregularities
indust
circumstellar
dust disks
Irregularities in
disks
indicate that the dust is concentrated in
orbital resonances with a planet. Planets
create “clumps” in the dust.
Infrared images of dust disks around 3 stars:
Vega
Fomalhaut
55 Cancri
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Extrasolar Planets
NASA’s new Spitzer
Space Telescope,
launched in August
2003, can detect dust at
various temperatures,
allowing it to provide a
full picture of the inner
region of disks such as
that around Fomalhaut,
25 light-years away.
Spitzer infrared image.
Fomalhaut is surrounded
by a dust ring nearly five
times larger than our own
solar system.
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Extrasolar Planets
The Future of Planet Hunting:
Astronomers will apply advancing
technology to the search for
extrasolar planets. One approach,
gravitational lensing, has been
used to search for brown dwarf
stars, and may be successful for
planetary searches, as it can detect
objects as small as the moon.
The Search For
Extrasolar Planets
Gravitational Lensing:
When a massive
object, such as a
star or a planet,
passes in front of
a star, it acts as a
lens, brightening
the image of the
star. Astronomers
can calculate the
mass of the object
by the degree to
which it affects
the brightness of
the star.
The Search For
Extrasolar Planets
An additional “blip”
in the light curve
may indicate the
presence of a planet
around the lensing
star, as shown in
this animation of an
actual microlensing
event.
The Search For
Extrasolar Planets
In 2004, a planet oneand-a-half times more
massive than Jupiter
was discovered orbiting
a red dwarf star 17,000
light years away. This
marks the first discovery
of an extrasolar planet
using gravitational
microlensing.
The Search For
Extrasolar Planets
First up in the future
of extrasolar planet
searches is NASA’s
Kepler Mission, due to
launch in 2007. Kepler
will take the transit
method to new
heights, continuously
monitoring over
100,000 stars from a
heliocentric orbit
slightly larger than
Earth’s.
Artist’s concept. Kepler will utilize
a specialized one-meter-diameter
telescope called a photometer.
The Search For
Extrasolar Planets
Previous studies have been limited to single
transits of gas giants too close to their suns to
support life. Kepler’s photometer, however, will
measure multiple transits of planets similar in size
– and possibly habitability – to Earth. Kepler will
also support the science objectives of two future
NASA missions, the Space Interferometry Mission
and Terrestrial Planet Finder.
The Search For
Extrasolar Planets
NASA is set to launch the Space Interferometry
Mission (SIM) in 2009. Unlike Kepler, SIM will
use astrometry to search for other planets.
The Search For
Extrasolar Planets
SIM will measure stellar “wobble” several hundred
times more accurately than current instruments do,
detecting much smaller planets than previously
possible.
The Search For
Extrasolar Planets
NASA’s Terrestrial
Planet Finder, set to
launch in 2012, will
detect Earthlike
planets up to 45 lightyears away with
imaging power
100x greater
than Hubble’s.
TPF’s concepts
include a
formation-flying
interferometer,
above, and
visible-light
coronagraph,
left.
The Search For
Extrasolar Planets
By combining highsensitivity space
telescopes with
revolutionary imaging
technologies, TPF will
study planets as small
as the Earth in the
habitable zones of
distant solar systems.
TPF's spectroscopy will
compare relative
quantities of gases to
determine whether a
planet could potentially
support life.
Artist’s concept of an
Earthlike planet.
The Search For
Extrasolar Planets
Will we discover other planets capable of
supporting life? Time will tell. One thing
is certain: however advanced technology
becomes, human curiosity and ingenuity
are the chief tools in the drive to solve
our mysteries.