Drake equation explained: How many extraterrestrial civilizations live in the Milky Way?

The Drake equation is used to calculate how many extraterrestrial civilizations are estimated to live in our galaxy, the Milky Way

Drake equation: Seven variables for one calculation

The Milky Way is the galaxy in which our solar system, and therefore Earth, is located. Given its size, it seems quite unlikely that we are the only inhabited planet. The Drake equation can be used to calculate the probability that someone is at home on the distant worlds.

• There are over 300 million worlds in the Milky Way that have Earth-like conditions, including the possibility of flowing water. So it seems only logical that we on Earth are not the only civilization in the galaxy.

• The Drake equation, which was established by Frank Drake in 1961, can be used to calculate the number of detectable civilizations in the Milky Way. The formula consists of seven different variables that are taken into account in the calculation. The Drake equation is: N = 𝑅𝑁* . 𝑓𝑝 . 𝑛𝑒 . 𝑓𝑙 . 𝑓𝑖 . 𝑓𝑐 . 𝐿

• N stands for the possible number of extraterrestrial civilizations in our galaxy and forms the result when all variables are multiplied.

• The variable 𝑅𝑁* stands for the average star formation rate per year in our galaxy. Thanks to the Hubble Space Telescope, this variable is quite predictable and is between four and 19 solar masses per year. We are only looking for stars that are comparable to the luminosity of our sun. Smaller stars have less luminosity and gravitational force, which means that planets can be subject to very high tidal friction, for example. Due to this bound rotation, one half of the planet would be constantly facing the star and hot. The other side would always be dark and cold.

• Stars that have a stronger luminosity than our sun, on the other hand, have too much magnetic activity and therefore stronger cosmic radiation. This is not exactly favorable for the development of life.

• 𝑓𝑝 is the proportion of stars with planetary systems. This raises the question of how many stars in the Milky Way are part of a planetary system. According to observations, around half of all stars belong to a planetary system – like our sun.

• The variable 𝑛𝑒 describes the average number of planets per star within an ecosphere. An ecosphere is the area in the planetary system in which life cannot be ruled out due to the prevailing physical conditions. Such a planet must not be too close or too far away in relation to the size of the star. The general search is for rocky planets with moderate temperatures that orbit sun-like stars – like our Earth.

• 𝑓𝑙 stands for the proportion of planets with life. This raises the question of how many planets in the ecosphere are home to life. So far, there are no scientifically verifiable figures for this, as we only know one example: our solar system.

• The variable 𝑓𝑖 denotes the proportion of planets with intelligent life. If life develops on a planet in an ecosphere, the question arises as to how highly developed and intelligent it is. Here, too, there is a lack of scientifically verifiable figures

• 𝑓𝑐 is the proportion of planets with an interest in interstellar communication. The question here is how many intelligent civilizations are interested in communicating with other individuals in the galaxy. The assumption is that only those interested in communication can be found.

• 𝐿 stands for the lifespan of a technical civilization, i.e. those that can receive a radio signal from space and send a signal into space, in years. Life on planets is threatened by internal and external influences. Entire civilizations can be wiped out by comet impacts, volcanic eruptions, a virus or the civilization itself. The life of a civilization ends at the latest when the planet dies. Every planet’s lifespan in a solar system is limited – among other things by the transience of the star.

Further life in the Milky Way is considered very likely

Between 37 and 60 percent of the sun-like stars in the Milky Way are thought to host a planet that offers a temperate and Earth-sized world for a civilization.

• According to calculations, the closest world to us is probably 20 light years away. Four such worlds can be reached within 33 light years. To put this into perspective: one light year is the equivalent of 9.5 trillion human years. That’s a long time.

• In general, other life in our galaxy is quite probable. This becomes even clearer when you consider that other life could already be discovered in our solar system. For example, it is assumed that the conditions for microbial life were present on early Mars.

• And if other life existed even in our solar system, then the probability that it is also possible in other solar systems increases enormously. Many scientists assume that, given the diversity of cosmic mass, biological life is not a coincidence but an inevitability.

• Thus, the Drake equation helps to determine how much potential life can be expected out there. Only one variable in the equation is difficult to answer: whether we humans are the only technological civilization on Earth. This question will only be answered when we perhaps one day receive a signal from space.