Ask Dr. SETI ®

Dear Dr. SETI:
I've just read your response in the article entitled "Estimating Drake Equation Factors", which was last updated in 2002. I'm wondering if you could revisit and revise this response to reflect our current knowledge of how prodigiously populated the Universe is with planets. Surely, we've found hundreds of planets since that had been written several years ago. Can you elaborate on how this would impact the outcome of the Drake Equation?
Steve B.

The Doctor Responds:
It's true, Steve, that we are entering a golden age of exoplanet discovery, with the Kepler spacecraft now giving us thousands of candidates, and potentially hundreds of newly discovered habitable planets. So, we have probably nailed down the second and third Drake Equation factors: lots and lots of planets (f_p approaching unity), and at least one "good Earth" per solar system (n_e pretty close to one). But this doesn't really bring us any closer to a "solution" to the Drake Equation then we were a decade ago! Let me explain:

When Frank Drake first penned this equation in 1961 (as simply an agenda for the world's first scientific SETI meeting), the only factor about which we could formulate even an educated estimate was the first one, the rate of stellar formation. Anything else was anybody's guess. We were, after all, multiplying seven things together (only one of which was even approximately known). Thus, estimates of N, the number of communicative civilizations in the milky way galaxy, ranged all over the map, from "none" to "billions and billions."

Well, it's been a productive half-century, and now we can make a reasonable guess as to the first three Drake factors. So, we can confidently multiply three things we know by four others that remain purely speculative. Estimates of N are still all over the map!

The fact is, we may never get a good estimate of N, until we've seen our own civilization live and die (providing us with an estimate of L, the longevity of technological civilizations in their communicative phase). When that happens, we will probably no longer care. So, the Drake Equation remains a marvelous tool for quantifying our ignorance.

Does this make the Drake Equation useless? Not at all! It was never intended for solving, but rather for helping us to know what we don't know. As such, it continues to guide and motivate our research, and in so doing, increase human knowledge (or, at least, decrease human ignorance, if only slightly.)

See Solving the Drake Equation for a further perspective on this question.