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There are 200 billion stars in our galaxy
one of them is our Sun.
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The sun has nine planets
we know of one that has life.
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Are there other planets in the universe?
Is there another Earth out there?
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Some planets were known to the ancients who
watched them move against the night sky.
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Mercury, Venus, Mars, Jupiter, and Saturn were
the Wandering Stars.
Planet comes from the Greek word for wanderer.
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Over the centuries, telescopes got better and
better
Galileo and his Refractive Telescope, 1609
Herschels Reflecting Telescope, 1789
The Hooker Telescope - Mount Wilson, ca 1920
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And other planets were discovered.
Uranus
The year 1781 The first planet discovered. Wi
lliam and Caroline Herschel

Neptune
The year 1846 First observed by Galle and d'Arr
est (based on calculations by Adams and Le Ver
rier).
Pluto
The year 1930 Discovered by Clyde Tombaugh
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But what about more distant worlds? Thousands of
years ago, Greek philosophers speculated.
There are infinite worlds both like and unlike
this world of ours...We must believe that in
all worlds there are living creatures and planets
and other things we see in this world.
Epicurius c. 300 B.C
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And so did medieval scholars.
The year 1584 "There are countless suns and count
less earths all rotating around their suns in
exactly the same way as the seven planets of our
system . . . The countless worlds in the
universe are no worse and no less inhabited than
our Earth Giordano Bruno in De L'infinito
Universo E Mondi
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And in the last hundred years, Hollywood came
knocking.
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While Hollywood worked on the public imagination,
scientists started to turn science fiction into
science fact.
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In 1995, a breakthrough the first planet around
another star.
Didier Queloz and Michel Mayor
A Swiss team discovers a planet 51 Pegasi
48 light years from Earth.
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Artist's concept of an extrasolar planet (Greg
Bacon, STScI)
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And then the discoveries started rolling in
New Planet Seen Outside Solar System
New York Times
April 19, 1996
10 More Planets Discovered Washington P
ost August 6, 2000
First new solar system discovered USA TODAY
April 16, 1999
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You can even see some of the stars
that have planets in the night sky
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if you know where to look
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Just how far are these new planets?
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But not far on a cosmic scale.
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How have we found all these planets?
Planet-hunters are detectives using powerful
telescopes and computers
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Scientists use the Doppler shift to measure the
tug of planets on stars. Here is how it works
If an unseen planet tugs the star back and forth
the light from the star shifts slightly to the
red as the star moves away from you.
and slightly to the blue as it moves toward you.
Astronomers can detect these shifts by very
carefully observing the spectra (or colors) of
the stars.
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But if the goal is to find planets with evidence
of life, the ones discovered so far are not good
candidates.
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Most of new discoveries are gas giants like
Jupiter or Saturn and in the wrong location.
The right location in our solar system.
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Many of the new planets get too hot or too cold
to support life.
Too cold!
Just right!
Too hot!
Most of them have highly elliptical orbits, or
are too close to their parent stars.
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Finding another Earth wont be easy because
1) Earth-like planets are small,
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The planets discovered so far are closer in mass
to Jupiter.
This is what weve found
This is what we are looking for
Jupiters diameter is eleven times greater than
the Earths, and it has over 300 times the mass.
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Stars are a billion times brighter
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than the planet
hidden in the glare.
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Like this
firefly.
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And how will we know a planet supports life?
Look for evidence of oxygen
Look for liquid water
Analyze the reflected light from the planet to
see if the planet has an atmosphere
Look for signs of biological activity (methane)
and rule out other explanations.
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And putting telescopes in space will help in the
search.
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So now the hunt for Earth-like planets really
blasts off
Keck Interferometer
Spitzer Space Telescope
Kepler
Large Binocular Telescope Interferometer
on the ground and in space.
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Terrestrial Planet Finder
Space Interferometry Mission
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As NASA gets ready to launch the most sensitive
instruments ever built.
And with these missions, we will use different
methods to find planets.
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For example, we will look for the stars light to
dim slightly when a planet passes in front.
This is called the transit method
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We will measure the tiny wobble of stars against
other stars in the background.
This is called astrometry
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We will block out the bright light from the star.
Telescopes that block the light from the central
star can take images of planets that might be in
orbit around them.
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And we will explore regions where planets formed
to get clues about the universe
In an early stage, before planets are formed,
some stars are shrouded in dense disks of gas and
dust.
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Over the next several years, we will continue to
try to answer the big question
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And one day, we might turn again to the poets and
philosophers
We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.
T.S. Eliot Four Quartets
For more information go to http//planetquest.jpl.
nasa.gov
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NASAs Vision To improve life here, To exten
d life to there,
To find life beyond.
Additional Information
Most of the missions depicted in this
presentation are a part of NASAs Navigator
Program. NASAs Navigator program is an integral
part of NASAs Astronomical Search for Origins
Theme, within NASAs Office of Space Science.
Kepler and the Spitzer Space Telescope are
not a part of the Navigator Program.
This presentation was created by the Navigator
Program Public Engagement team.
For more information go to http//planetquest.j
pl.nasa.gov
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