Transcript Astrobiology

Astrobiology
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
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
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.
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
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.
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
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
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