1. Astrobiology

2. Primordial Soup Life on Earth is comprised of relatively few elements. –Basic elements: carbon, nitrogen, oxygen, hydrogen –Trace elements: iron, calcium, potassium, phosphorus,... We observe these in compounds on other planets. –Methane, ammonia, water –Minerals with silicon, calcium, iron

3. Recipe for Life In 1952 Urey and Miller placed water and gases in a flask. –Simulate early planet –Spark as lightning Amino acids were present in a week. –Building blocks of proteins

4. Past Life On Earth life began after about 1 billion years. –One-celled creatures for the next 2.5 to 3 billion years –Extremophiles and cyanobacteria need no oxygen Multi-celled creatures began about 600 million years ago.

5. Star Types To have an Earth-like planet we need Earth’s conditions. –Assume carbon-based life Stars can’t be too large. –Lifetime of more than 1 billion years Stars can’t be too small. –Close planet for heat –Tidally locked with no day-night cycle

6. Galaxy Types Heavy elements (metals) exist in type I star populations. Elliptical galaxies and halo clusters are poor in metals. Metals are best in the spiral disk.

7. Galactic Zone The habitable zone in the galaxy may be narrow. –Too much radiation near center –Too little gas for planets far out The best zone is 4.5 to 11.5 Kpc from the center. –Includes 20% of the Milky Way

8. Planetary System Planets can’t be too large or too small, too hot or too cold. A binary system or cluster would be bad. –Complicated orbits –Large temperature changes

9. Planetary Zone For a single star with a system of planets there is an ideal zone of orbits. The orbits must be in a range that creates temperatures suitable for water. too hot too cold