Drake equation

The Drake Equation is a mathematical formula used to estimate the number of intelligent extraterrestrial civilizations in the Milky Way galaxy. Written by American astronomer Frank Drake in 1961, the equation multiplies several astronomic figures to calculate the probability of humans discovering advanced life elsewhere in space. Until more information about such life becomes available, the Drake Equation will continue to offer only loose and open-ended answers to the question of intelligent extraterrestrial life in the universe.

History of the Equation

The history of the Drake Equation began in April of 1960, when the young American astronomer Frank Drake was leading Project Ozma for the National Radio Astronomy Observatory (NRAO). Developed by Drake himself, Project Ozma was the United States' first search for radio communications from the distant universe.

Over a period of two hundred hours, Drake aimed the observatory's eighty-five-foot radio telescope at Tau Ceti and Epsilon Eridani, two nearby stars that closely resemble Earth's sun. Project Ozma ultimately detected no interstellar communications or other signs of extraterrestrial intelligence, though the American public and Drake's fellow scientists found the venture fascinating.

To capitalize on the project's ambitions, NRAO held an "Extraterrestrial Intelligent Life" conference in November of 1961 in Green Bank, West Virginia. The conference was to focus on the possibility of detecting extraterrestrial life, but Drake was given freedom to structure the discourse as he saw fit.

He ultimately devised a mathematical formula that incorporated all the estimated factors in the question of whether extraterrestrial life existed. The formula, which came to be called the Drake Equation, was relatively simple. It consisted of seven factors multiplied to yield an approximate number of areas in the galaxy that could host intelligent, communicating civilizations. The equation's uncomplicated design was intentional, as Drake hoped astronomers could continue to use it for many years as new information about the universe became available.

The Equation

The Drake Equation is written in the following form:

N = R^*• f_p • n_e • f_l • f_i • f_c • L

Each letter represents a different factor in the calculations to determine the locations in the Milky Way that could most likely be inhabited by intelligent life:

• N = the approximate number of civilizations that emit detectable electromagnetic signals
• R^* = the rate of the creation of stars that could support life on nearby planets
• f_p = the fraction of these stars that hosts planetary systems
• n_e = the number of planets in each solar system that could support life
• f_l = the fraction of these planets that actually supports life
• f_i = the fraction of life-supporting planets that hosts intelligent life
• f_c = the fraction of civilizations that emit detectable evidence of their existence into space
• L = the length of time these civilizations have emitted detectable signals into space

Though Drake's equation presented all the factors necessary for finding the probability of the existence of intelligent life in the Milky Way, none of the formula's variables could actually be known with certainty—the vastness of space and the limits of space technology in 1961 prevented astronomers from comprehensively searching the galaxy for signs of intelligent life.

Applying the Equation

Inadequate technology for exploring the entire Milky Way continued to present a problem for astronomers into the late twentieth and early twenty-first centuries. A significant event in the mid-1990s, however, changed the way astronomers viewed the prospect of extraterrestrial life existing somewhere in the galaxy. This was the discovery of the first exoplanet, 51 Pegasi b, in 1995. An exoplanet is a planet located outside the solar system, of which the sun is the center.

The identification of 51 Pegasi b allowed astronomers to begin locating hundreds and then thousands of other exoplanets scattered across the Milky Way. Initially, this could be done by observing the planets transiting across their stars—which caused a measurable dimming of the star—or by measuring the gravitational fluctuations caused by the planets' orbiting around their stars. In the late 2000s, the National Aeronautics and Space Administration (NASA) launched the Kepler spacecraft to search for additional exoplanets. Within only a few years, more than 1,700 exoplanets had been confirmed to exist inside the Milky Way.

Even after these discoveries, however, scientists still struggled to identify all the factors the Drake Equation required to provide an approximate number of intelligent extraterrestrial civilizations in the galaxy. This is because of the infrequency of discovered exoplanets being actually suitable for life; in 2014, after studying the nearly two thousand confirmed exoplanets in the Milky Way, astronomers named only twenty that could possibly support life, based on the planets' atmospheric conditions and distances from their stars.

Any discovery of extraterrestrial life in the galaxy or the larger universe would allow scientists to apply more accurate information to the Drake Equation and ultimately better understand the conditions necessary for life to exist off the planet Earth. Meanwhile, NASA astronomers have beamed radio messages into space and even included a record of information about Earth aboard the Voyager spacecraft to inform any potential intelligent lifeforms in the universe of the existence of humans and their planet. As more information about extraterrestrial life is discovered, the Drake Equation will become a more valuable tool to astronomers.

Bibliography

Dick, Steven J. "Introduction: The Drake Equation in Context." The Drake Equation: Estimating the Prevalence of Extraterrestrial Life through the Ages, edited by Douglas A. Vakoch and Matthew F. Dowd. New York: Cambridge University Press, 2015, 1-3. http://assets.cambridge.org/97811070/73654/excerpt/9781107073654‗excerpt.pdf

"The Drake Equation." SETI Institute. SETI Institute. Web. 30 Nov. 2015. http://www.seti.org/drakeequation

Howell, Elizabeth. "Drake Equation: Estimating the Odds of Finding E.T." Space.com. Purch. 26 Mar. 2014. Web. 30 Nov. 2015. http://www.space.com/25219-drake-equation.html