The famous Drake equation gave a range of a minimum of 20 civilizations to a maximum of 50,000,000 alien civilizations.
In 1961, astronomer and astrophysicist Frank Drake developed an equation to estimate the number of active extraterrestrial civilizations in the Milky Way galaxy, using factors such as the rate of star formation, the number of planets, the duration of intelligent civilizations needed to release detectable signals into space, and others. The famous Drake equation gave a range of a minimum of 20 civilizations to a maximum of 50,000,000 alien civilizations.
James Benford, a physicist at Microwave Sciences in Lafayette, California (USA), developed his version of the Drake equation to search for signs of extraterrestrial artifacts (SETAs), which we should find on the Moon. In a study published in the journal Astrobiology, James Benford presents his justifications for SETA, with artifacts lasting much longer than signals, and they can even be left by aliens who don’t want to be discovered. In addition, artifacts can be found on planets and space bodies that do not necessarily show signs of life, such as the Moon.
Benford believes the SETA indicator is more appealing because it involves an active search, while SETI is more of a passive approach of sitting and waiting for a signal. Also, artifacts are a better sign of an advanced intelligence capable of traveling long distances, whereas we humans are capable of sending signals but don’t travel very far into outer space.
The researcher also says that we need to use Artificial Intelligence software to search for artificial structures. Benford claims that the Lunar Reconnaissance Orbiter spacecraft has taken about 2 million pictures of the Moon since 2009, but they have not been analyzed for signs of artifice.
He believes that the solar system could have been visited by aliens, who were on the planets of some suns that passed close to the Sun (for example, Scholz’s star came within only 0.82 light-years of the Sun only 70,000 years ago for years). Aliens from these star systems could have sent robotic probes to explore our solar system.