Database Of Exoplanets
An exoplanet or extrasolar planet is a planet outside the Solar System. Typically these orbit around stars, and until recently their existence was merely theorized. Now that advanced space observation technology has demonstrated that "exoplanets are real", it is now regarded as quite "normal" for stars to have planetary systems.
As of April 2019, 4,023 exoplanets have been confirmed, in 3,005 star systems - with more being discovered all the time. Larger planets closer to their host star are generally the easiest to detect, as these leave a more readily measurable dip in the light received from that star when they transit. This method, "transit photometry", is currently the most effective however there are several other methods of detecting exoplanets.
Around 1 in 5 "sun like" stars have an approximately earth-sized planet within the "habitable zone" - which has increased the perceived likelihood of the discovery of life on these worlds.
There are also rogue planets which do not orbit any star. It has been hypothesized that there may be billions of these in our galaxy alone.