Dr. Frank Drake serves on the Board of Trustees of the SETI Institute. In 1960, as a staff member of the National Radio Astronomy Observatory, he conducted the first radio search for extraterrestrial intelligence. He developed the Drake Equation in 1961 as a way to illustrate the factors that determine how many intelligent, communicating civilizations there are in our galaxy. It does provide us with a clear idea of what questions we must continue to answer in order to understand our existence in the universe. Its effective rational has helped it serve as the backbone in support of the SETI project for over 40 years despite no known values for the variables and no solution to the equation. The Drake Equation is:

N  =  R*  fp  ne  fl  fi  fc  fL

N    is the number of communicating civilizations in our galaxy. Which is equal to the product of the 7 independent variables.

R*    represents the rate at which stars suitable for hosting life form within the galaxy, expressed in stars per year. This is the only variable in the equation that is known with accuracy. Since there are roughly 100 billion stars in the Milky Way and the galaxy is approximately 10 billion years old, R* is estimated as approximately 10 stars per year. According to the equation, a higher rate of stars suitable for hosting life means a higher number of transmitting civilizations in our galaxy. Because it is calculated based on the total number of stars in the Galaxy, the star formation rate would be differ if our estimates of the Milky Way size were incorrect. Also, it is possible that the star birthrate has decreased or increased over time meaning less or more transmitting civilizations (evidence suggests it has decreased).

fp    is the fraction of stars suitable for hosting life that have planets around them Astronomers have been trying to deduce this variable by observing the presence of planets around other stars, which is difficult to do without directly imaging distant stellar systems. Most stars occur in multiple systems, in which there is less likely to be planets with stable orbits like our own. Nonetheless, it is believed that most sun-like stars host planets. Estimates have ranged between 20 and 50%.

ne    is the number of planets per solar system that are capable of sustaining life. By examining our own solar system we can gauge estimates for this variable. Assuming that liquid water is a necessary element for sustaining life, we believe that Earth, Mars, Europa, and Titan may lie within this parameter. The giant gas planets are entirely too unknown for us to postulate whether they were ever capable of sustaining life. Thus, the estimates for this variable usually range between 1 and 5.

fl    is the fraction of planets in ne where life is known to evolve. This is an extremely uncertain variable, as knowledge of evolutionary life elsewhere is merely speculatory. Current estimates range from 100% (where life can evolve it will) down to close to 0%.

fi    is the fraction of fl (inhabited planets) where intelligent life evolves. Again, this variable is much more speculatory. Some planets may be host to living organisms that would eventually become intelligent but for a catastrophic event or other hindrances. Estimates range from 100% (intelligence is such a survival advantage that it will certainly evolve) down to near 0%.

fc    is the fraction of fi (intelligent planets) that have the ability to communicate beyond their world. This variable requires even more speculation. It is certainly plausible that intelligent beings never develop technology i.e. dolphins, or decide against transmitting any communication.

fL    is the timeframe that the communicating civilizations transmit signals. This is the toughest of the questions. If we take Earth as an example, the expected lifetime of our Sun and the Earth is roughly 10 billion years. So far we've been communicating with radio waves for less than 100 years. If our earth blew up tomorrow, the answer to this question would be 1/100,000,000th. If we survive and continue to transmit signals for 10,000 years the answer will be 1/1,000,000th. This has profound implications for the solution to the equation.

  *******The questions that are prompted when attempting to come up with a solution are more important than solving the numerical equation, which may never be achieved. There is much speculation required to assign values to each variable, but as we learn more from our advances in science and technology, we will be able to better estimate the answers and gauge our position.*******



                                                    

Nicholas Friedman
Gavin Cree