## Friday, September 18, 2009

### The Drake Equation

Ever heard of the Drake equation? Devised by Dr. Francis Drake in 1960, the equation estimates the number of extraterrestrial civilizations in our galaxy with which we might come into contact. The main purpose of the equation is to allow scientists to quantify the factors that determine the number of such extraterrestrial civilizations.

The Drake equation states that:

$N = R^{\ast} \times f_p \times n_e \times f_{\ell} \times f_i \times f_c \times L \!$

where:

N is the number of civilizations in our galaxy with which communication might be possible;

and

• R* is the average rate of star formation per year in our galaxy
• fp is the fraction of those stars that have planets
• ne is the average number of planets that can potentially support life per star that has planets
• f is the fraction of the above that actually go on to develop life at some point
• fi is the fraction of the above that actually go on to develop intelligent life
• fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
• L is the length of time such civilizations release detectable signals into space.
Here were the values used by Drake and his colleagues in 1961:
• R* = 10/year (10 stars formed per year, on the average over the life of the galaxy)
• fp = 0.5 (half of all stars formed will have planets)
• ne = 2 (stars with planets will have 2 planets capable of supporting life)
• f = 1 (100% of these planets will develop life)
• fi = 0.01 (1% of which will be intelligent life)
• fc = 0.01 (1% of which will be able to communicate)
• L = 10,000 years (which will last 10,000 years).
This gives N = 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 10,000 = 10.

As you can imagine, there is considerable disagreement on the chosen values for the parameters. Since it first came to being, other factors have been included to the equation. In my view, the Drake equation is merely a shot in the dark. But the effort is applaudable. After all, it has inspired researchers to pursue another equation to determine how suitable a planet is for life. What is your equation?

- PTS