35 extraterrestrial civilizations in the Milky Way

Nottingham (England). Scientists of the University of Nottingham have calculated that there could be 35 intelligent, actively communicating civilizations in our galaxy besides mankind. The study published on the preprint server arXivpubliziert on the Preprint server arXiv is based on statistical data, which the astronomy in the past decades over the Milky Way collected.

According to Christopher Conselice, professor for astrophysics, “the computation is quite simple”, although mankind is at present the only well-known civilization in the entire universe. As Conselice explains, “scientists know enough about stars, planets and our galaxy and their evolutionary history to be able to make this calculation.

Living conditions on earth

As a basic assumption, the scientists used the conditions on earth, which make it possible for intelligent life to develop on our planet. They then calculated how many exoplanets of similar size lie within the Milky Way in the habitable zone of their star, i.e. are neither too hot nor too cold for life.

According to Conselice, the basic idea is therefore that “science works the same way everywhere in the universe. If all criteria for intelligent life as on Earth are fulfilled, according to the scientists’ theory, “at some point” intelligent life will also develop. According to the authors of the study, “a few billion years” will play practically no role.

Current Drake equation

The physicist Frank Drake presented the Drake equation, a calculation method for the number of intelligent life forms in the Milky Way, as early as 1961. According to Drake, the calculation only requires the multiplication of seven factors, which are all unknowns. The new method can, therefore, be called Drake equation 2.0.

The new Drake equation takes into account the total number of stars in the Milky Way, the proportion of stars with an age of at least five billion years, and the proportion of stars in the habitable zone. In contrast to the first version of the Drake equation, the number of required magnitudes is thus significantly smaller and can be determined from current observational data.

Only the fourth quantity, i.e. the average lifetime of a civilization starting from the time, from which it can send signals as radio waves out into space, divided by the period needed, until life develops on a habitable planet, could also the authors of the current study only estimate. They developed, therefore, a set of scenarios, which indicate from conservatively to optimistically four to 211 actively communicating civilizations in our galaxy. 36 intelligent forms of life including mankind are most likely.

17,000 light-years distance

In addition to the number of extraterrestrial civilizations, the scientists also calculated the probable distance, which according to them is on average 17,000 light-years. Detection of possible communication is therefore impossible with the current technology.

Hope for soon contact makes, however, the minimum distance, which lies according to the calculations with only a few hundred light-years. However, this is only plausible if the lifetime of an intelligent civilization is at least one million years. Conselice states that “this seems very long if we look at our civilization. He further explains that “if we were to find many extraterrestrial civilizations very close, this means that they have managed to exist for long periods despite problems such as global warming or wars.

Billions of habitable exoplanets in the Milky Way

The Milky Way could be home to several billion Earth-like planets. Not only that, there is the possibility that these are as habitable as the earth. The stars around which they orbit are even visible to the naked eye and are part of our galaxy.

Berkeley (U.S.A.). The nearest sun-like star is about twelve light-years away from our home planet. Not only that, but there are even conditions for an Earth-like planet, according to Erik Petigura of the University of California at Berkeley. He and his colleagues Andrew W. Howard and Geoffrey W. Marcya, evaluated data from the Kepler Space Telescope. The statistical impact of our galaxy shows the occurrence of 100 billion sunlike stars. In addition, a two-digit billion number of Earth-like planets are said to exist. However, it is completely unclear whether there are also life-friendly conditions on these planets. After all: Every fifth sunlike star binds a planet to itself that has habitable zones. For this to be possible, several conditions must be present.

Firstly, there must be a certain distance between an Earth-like planet and the sun that the planet orbits. If the planet with its orbit is too close to the star, it would be too hot there, if it is too far away, it would be too cold. Furthermore, the atmosphere and geological conditions on the planet would have to be right for life — at least as we know it — to exist at all. The researchers around Erik Petigura took up these parameters and made an appropriate selection of the possible celestial bodies. From this a percentage probability results that approximately 22 per cent of the stars, the conditions for earthsimilar planets bring with itself. In all probability, these planets also have zones where life is possible or at least can develop there.

Even though the estimated number of stars and their planets is very high, the measurements of the Kepler telescope confirmed so far show that of about 600 planets, only a fraction, namely ten, fulfill these conditions for life. These conditions include the presence of liquid water.