Artwork: The Kepler telescope was launched to detect new worlds using the "transit method"
It's the largest number of worlds ever discovered in a planetary system outside our own.
The star known as Kepler-90, is just a bit hotter and larger than the Sun; astronomers already knew of seven planets around it.
The newly discovered world is small enough to be rocky, according to scientists.
"This makes Kepler-90 the first star to host as many planets as our own Solar System," said Christopher Shallue, a software engineer at Google, which contributed to the discovery.
Engineers from Google used a type of artificial intelligence called machine learning to find planets that were missed by previous searches.
Image caption Artwork: The Kepler telescope was launched to detect new worlds using the "transit method"
The discovery was based on observations gathered by Nasa's Kepler Space Telescope.
Its parent star is very distant, lying 2,545 light-years away. But its planetary system appears to be ordered in a similar way to our own.
Andrew Vanderburg, a co-discoverer at the University of Texas at Austin, said: "The Kepler-90 star system is like a mini version of our Solar System. You have small planets inside and big planets outside, but everything is scrunched in much closer."
To give a sense of how close, the outermost planet in the system orbits at around the same distance the Earth does from the Sun.
Because the new world, dubbed Kepler-90i, is so much further in - it completes one circuit of its star every 14.4 days - it's estimated to have a scorching hot surface temperature of around 425C.
The machine learning technique was also used to find a new Earth-sized planet, called Kepler 80g, around a different star.
Some 3,500 exoplanets - worlds circling other stars - have been documented in recent decades.
Source: Star system has record eight exoplanets
