We received the following question from one of our readers:
As of May 2020, the existence of 4,264 exoplanets in 3,152 star systems has been reliably confirmed, with more than 3.5 thousand more reliable candidates for exoplanets currently awaiting re-confirmation for final recognition.
According to the same data, only 697 systems are known that include more than one planet, that is, on average, there are slightly more than one planet in planetary systems. However, this does not mean that in most star systems of the galaxy there is only one planet, it does not even mean that in the data, open systems, there is only one planet.
In fact, in systems where we have discovered only one planet, there may be many other, not yet discovered planets. Modern methods of searching for exoplanets make it possible to detect only sufficiently large and close to the star planets, it is quite possible that in known systems there are remote from the star or small exoplanets that we have not yet managed to fix, in some systems only one planet has been reliably confirmed at the moment, and a few more are awaiting confirmation.
Personally, I have come across in the literature with systems in which the number of exoplanets is estimated up to six, if there are systems with a higher estimate, then I have not come across data on them.