Astrobiology

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. 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. Galaxy Types

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