Where Have Your Atoms Been?

1. Where Have Your Atoms Been? • The universe was created in the big bang 13 to 15 billion years ago • The hydrogen in the water in your body was created then • More complex atoms had to be “cooked” inside stars • Several generation of stars had to pass with the most massive stars exploding • Interstellar gas was enriched with heavier elements • Interstellar dust formed containing these elements Lecture 35

2. Local Action • About 5 billion years ago, a cloud of gas and dust began to collapse under its own weight and formed our solar system • The Earth was formed and its atmosphere allowed liquid water to exist on the surface • The chemical makeup of Earth may have been influenced by complex materials from comets • Earth’s evolution was punctuated with asteroid strikes • Cosmic evolution Lecture 35

3. The Copernican Principle • The idea that there is nothing special about our place in the universe is called the Copernican principle • There are 200 billion stars in the Milky Way and there are 200 billion other galaxies • The chances that life is limited to our planet seem small • However, science demands proof • The search for extraterrestrial life • Some have been done • More are being done Lecture 35

4. The Building Blocks of Life • No unambiguous evidence for life beyond Earth has been found • Evidence for the building blocks of life has been found • Meteorites have amino acids • Comets show organic molecules • Organic molecules have been found in interstellar gas and dust clouds • In the 1950s, Miller and Urey simulated the conditions on an early Earth and produced many of the building blocks of life Lecture 35

5. Life in the Solar System • Recent work on a meteorite ALH 84001 suggested that it contained fossilized life from Mars • Very controversial • Recent pictures from the Mars Global Surveyor show evidence for recent water flows less than a million years old • Water flows are thought to have come from underground aquifers • Still under debate • Life was observed near black smokers under the ocean sparking interest in observing similar life extraterrestrially Lecture 35

6. Possible Water Flow on Mars • North wall of crater in southern hemisphere • Nirgal Valles, valley system cut by running water • Close-up of Nirgal Valles wall • Gullies on the wall of 20 km wide impact crater in Noachis Terra Lecture 35

7. Traveling to Other Stars • In our fastest spacecraft, it would take 80,000 years to reach the nearest star • If you wanted to reach the nearest star and return in your lifetime, you would need to travel near the speed of light (8 LY round trip) • Even with a perfect engine, this trip would take a huge amount of energy • 500,000 years of the US electrical consumption • These calculations casts doubt on UFO sightings • There have been no verified UFO sightings Lecture 35

8. Communicating with the Stars • We have 4 spacecraft that have left the solar system • 2 Pioneers and 2 Voyagers • They will take hundreds of thousands of years to even approach another star • We put messages on these spacecraft • Each Pioneer carries a gold-anodized plaque with a pictorial message • Each Voyager carries audio-visual recording with photographs and music Lecture 35

9. Messages in a Bottle Voyager’s Message Pioneer’s Message Lecture 35

10. The Search for Extraterrestrial Intelligence • Direct visits are unlikely so we must exchange messages • Listening with radio waves is the most likely way of hearing extraterrestrial messages • This effort is challenging and success is not likely even if there is extraterrestrial intelligence • If we do receive a signal, what should we do? Lecture 35