The Drake Equation Revisited

The Drake Equation is an equation for estimating how many communicative civilizations there are in our Galaxy, by breaking the problem down into more tractable ones. It was proposed by astronomer Frank Drake in 1961.
Drake Equation at Wikipedia
Drake Equation | SETI Institute
NOVA | The Drake Equation
The Drake Equation revisited: An interview with Sara Seager

N = Rs * fp * ne * fl * fi * fc * L

• N = number of communicative civilizations in our Galaxy
• Rs = rate of star formation in our Galaxy
• fp = fraction of stars with planets
• ne = fraction of planets that are Earthlike
• fl = fraction of Earthlike planets where organisms emerge
• fi = fraction of planets with biotas where intelligent life emerges
• fc = fraction of planets with intelligent life where interstellar-communication ability emerges
• L = lifetime of a communicative civilization

When this equation was proposed, the only number that we had a good handle on was Rs. Today, with numerous exoplanets discovered, we are starting to get a clue about fp and ne. In particular, planetary systems seem to be common, making fp not much less than 1. But the remaining factors, fl, fi, fc, and L, continue to be very difficult. I will discuss them in my next posts.