2 There are 200 billion stars in our galaxy… …one of them is our Sun.

The sun has nine planets… …we know of one that has life.

2 Is there another Earth out there? Are there other planets in the universe?

2 Some planets were known to the ancients who watched them move against the night sky.

Mercury, Venus, Mars, Jupiter, and Saturn were the “Wandering Stars.” “Planet” comes from the Greek word for “wanderer.”

Over the centuries, telescopes got better and better… Galileo and his Refractive Telescope, 1609Herschel’s Reflecting Telescope, 1789 The Hooker Telescope - Mount Wilson, ca 1920

And other planets were “discovered.” Uranus Pluto Neptune 5 The year 1781 The first planet “discovered.” William and Caroline Herschel The year 1846 First observed by Galle and d'Arrest (based on calculations by Adams and Le Verrier). The year 1930 Discovered by Clyde Tombaugh

“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 But what about more distant worlds? Thousands of years ago, Greek philosophers speculated.

And so did medieval scholars. The year 1584 "There are countless suns and countless 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 4

And in the last hundred years, Hollywood came knocking.

While Hollywood worked on the public imagination, scientists started to turn science fiction into science fact.

In 1995, a breakthrough: the first planet around another star. A Swiss team discovers a planet – 51 Pegasi – 48 light years from Earth. Artist's concept of an extrasolar planet (Greg Bacon, STScI) 7 Didier Queloz and Michel Mayor

And then the discoveries started rolling in: “First new solar system discovered” USA TODAY April 16, 1999 “10 More Planets Discovered” Washington PostAugust 6, 2000 “New Planet Seen Outside Solar System” New York Times April 19, 1996

You can even see some of the stars that have planets in the night sky…

…if you know where to look

Just how far are these new planets? from Mars… it would take ten minutes from the nearest extrasolar planet… it would take over ten years! from the Moon… it would take one second IF YOU WANTED TO RADIO HOME FOR YOUR WORDS TO REACH EARTH

But not far on a cosmic scale. would be the size of the United States. Our Milky Way Galaxy where we’ve found new planets would only be the size of Manhattan. And the neighborhood Our whole Solar System would be this big Imagine, if you shrunk our solar system to a little larger than a quarter:

Planet-hunters are detectives using powerful telescopes and computers 9 How have we found all these planets?

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.

But if the goal is to find planets with evidence of life, the ones discovered so far are not good candidates.

17 Most of new discoveries are gas giants like Jupiter or Saturn and in the wrong location. The right location in our solar system.

Most of them have highly elliptical orbits, or are too close to their parent stars. Many of the new planets get too hot or too cold to support life. Too hot! Too cold!Just right!

Finding another Earth won’t be easy because: 1) Earth-like planets are small, 2) Planets are relatively close in to bright stars. and

The planets discovered so far are closer in mass to Jupiter. Jupiter’s diameter is eleven times greater than the Earth’s, and it has over 300 times the mass. This is what we are looking for This is what we’ve found

Stars are a billion times brighter…

…than the planet …hidden in the glare.

Like this firefly.

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. 17

And putting telescopes in space will help in the search. This is from the groundThis is from space

19 So now the hunt for Earth-like planets really blasts off… …on the ground and in space. Keck Interferometer Spitzer Space Telescope SIM PlanetQuest Kepler Large Binocular Telescope Interferometer Terrestrial Planet Finders

For example, we will look for the star’s light to dim slightly when a planet passes in front. NASA’s Kepler Mission will hunt for planets using a specialized one-meter diameter telescope called a photometer to measure the small changes in brightness caused by these passing planets (or transits). This is called the transit method

We will measure the tiny wobble of stars against other stars in the background. SIM PlanetQuest will determine the positions of stars several hundred times more accurately than anything previously possible, helping to pin-point Earth-sized planets. This is called astrometry

Telescopes that block the light from the central star can take images of planets that might be in orbit around them. The Keck Interferometer combines the light of two 10- meter telescopes to take images of hot Jupiter-size planets that shine bright in infrared light. Keck Interferometer The Terrestrial Planet Finder Coronagraph (left) and Interferometer The two Terrestrial Planet Finder observatories will search from space for planets as small as Earth and for signs about whether they can support life. We will block out the bright light from the star.

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. Launched in 2003, the Spitzer Space Telescope is using its infrared camera to study the beginnings of planetary systems. Spitzer Space Telescope

Over the next several years, we will continue to try to answer the big question: June 4, 2003

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 26 And one day, we might turn again to the poets and philosophers…