Aliens may not make contact with humans for another 400,000 years, according to a new study.
Latest research into what scientists call Communicating Extraterrestrial Intelligent Civilizations (CETIs) has been looking into how many there might be in Planet Earth 's galaxy - the Milky Way.
While boffins are unable to say how many other CETIs exist in the Milky Way, a separate study in 2020 estimated that there are likely to be 36.
That study, by the University of Nottingham, used calculations involving galactic star formations and the likelihood of stars hosting Earth-like planets in their habitable areas.
While its authors admitted that scientists can only speculate on the number of CETIs in the Milky Way until any positive detection is made, they added that it remained possible to create models for "plausible estimates of the occurrence rate of such civilisations".
A new study by Wenjie Song and He Gao from Beijing Normal University builds on that past research.
Their paper deals with two parameters: firstly, how many terrestrial planets are habitable and how often life on these planets evolves into a CETI, and secondly at which stage of a host star's evolution a CETI may be born.
Using a series of modelling scenarios based on these parameters the researchers arrived at an optimistic and pessimistic forecast for how long it would take for such civilisations to make contact with humankind.
In the optimistic scenario, a star had to be at least 25 per cent into its lifetime before a CETI can emerge and for each of the life-supporting planets in its solar system, there was a 0.1 per cent chance of a CETI appearing.
This scenario creates more than 42,000 CETIs in the Milky Way. Based on this, it was concluded that humans would have to wait around 2,000 years to establish contact with aliens.
Under the pessimistic scenario, a star needed to be at least 75 per cent into its lifetime before a CETI can emerge and for each terrestrial planet, there was only a 0.001 per cent chance of a CETI appearing.
These circumstances created just 111 CETIs in Earth's galaxy, meaning it would take aliens another 400,000 years to communicate with humans.
The study, published in The Astrophysical Journal, argues that humans may never communicate with aliens - particularly in the pessimistic scenario - because factors like population issues, nuclear annihilation, sudden climate change, rogue comets and ecological changes could lead to humanity's extinction before 400,000 years elapse.
