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

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

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%

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%

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)

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 – 0.00000001 (0.000001%) Optimistic estimate – 1 (100%)

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 – 0.000001 (0.0001%) 1 in a million worlds Optimistic estimate – 1 (100%) Every habitable world

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 – 0.000001 (1 in a million) Optimistic estimate – 1 (100%)

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 – 0.000001 (1 in a million) Optimistic estimate – 0.1 (10% - 1 in 10 civilizations)