1. Is there life on other worlds? If so, how many?
The Drake Equation
Is there life on other worlds? If so, how many?

2. Total number of stars in the Milky Way galaxy
Based on images from Hubble & other deep space telescopes
Sample sections the galaxy (count stars in star clusters)
Estimate size of star clusters
Extrapolate to size of our galaxy
There are between 100B-600B stars in the Milky Way using various estimation techniques
Most scientists believe the number is close to 400B

3. Percent of stars that are “appropriate”
Most scientists believe that a star has to be like our sun
Main Sequence G-Type star
5% of all stars
10% are closely related F & K type stars
Many stars exist in a binary (or more) system which some scientists feel make them inappropriate
Estimates for appropriate systems are between 5-45%

4. Percent of appropriate stars that hve planetary systems
We have only just begun detecting extra-solar planetary systems around stars
Kepler space telescope
Some planets we see and some are detected by measuring the diminishing light/wobble of stars
Conservative estimate – 5%
Optimistic estimate 50%-100%

5. Average number of habitable planets or moons
Our only official example is our own solar system
Is Earth the only life-forming body?
How typical is our solar system?
Remember, this is an averaged value across all star systems
Conservative estimate 0.1 (1 in every 10 systems)
Optimistic estimate 4 (4 in every system)

6. Percent of habitable worlds that develop life
No real data are available to help estimate this term
Earth is only known planet to harbor intelligent life
Earth had bacterial life very early after it’s creation (early as 100MY after cooling!)
This may indicate that development of life is easy
Conservative estimate – ( %)
Optimistic estimate – 1 (100%)

7. Percent of planets with life that develop intelligent life
Somehow, humans gained an evolutionary advantage over every other species to develop the level of intelligence we have
How do you define intelligence? (Dolphins, whales, octopus?)
Single-cellular life quick (100MY)
Multicellular life 2.5BY on Earth
Conservative estimate – (0.0001%) 1 in a million worlds
Optimistic estimate – 1 (100%) Every habitable world

8. Percent of intelligent life that develops radio technology
Radio waves travel at the speed of light
As far as we know, nothing travels faster than light speed
Radio technology was created on Earth about year 1900 (4.5BY after Earth’s creation)
How long does it take for an “intelligent” civilization to produce radio waves?
Humans (homo sapien-sapien) 200K-400K YA (4.2BY-4.4BY after Earth cooled
Conservative estimate – (1 in a million)
Optimistic estimate – 1 (100%)

9. Percent of “current” civilizations having radio tech trying to contact us
Signals from ET’s whose civilization died off 100MYA and are 100M light years away took 100MY to get here
How long do civilizations with radio technology last?
Did they all destroy themselves with nuclear weapons long ago?
Worlds smashed by comets or gamma ray bursts?
Perhaps they survive a long time if they can travel to other habitable worlds
Can ET’s communicate with us via sub-space transmission, inter-dimensional transmission or using optical fiber tech? How would we hear those??
Are we interesting enough to communicate with for an ET?
Conservative estimate – (1 in a million)
Optimistic estimate – 0.1 (10% - 1 in 10 civilizations)