PixelHive/Shutterstock
When we talk about our own solar system, we’re referring to the unique collection of eight planets and five dwarf planets that orbit our Sun—Sol, the Latin name for the star that has been the centerpiece of human astronomy for millennia. Yet this is only one of billions of similar systems scattered across the cosmos.
A star system is a group of planets, meteoroids, or other bodies bound to a star—or, in some cases, to multiple stars. Some systems contain a single luminous body, while others, like the Trappist‑1 system, have up to seven stars orbiting one another. The Milky Way itself is estimated to host between 100 billion and 400 billion stars, but the exact count remains elusive, and so does the tally of its star systems.
Why, then, can’t we simply extrapolate from our knowledge of the galaxy’s size and the presence of exoplanets to arrive at a reliable number? The answer lies in the sheer scale of the Milky Way and the difficulty of detecting planets around distant stars—a challenge that has occupied astronomers for over three decades.
Sciepro/Getty Images
Our galaxy stretches roughly 100,000 light‑years across—a distance that already feels almost unfathomable. Even within that breadth, the Milky Way contains a staggering number of stars, and each of those stars likely hosts its own planetary system. However, our current knowledge is still evolving.
The nearest multi‑star system, Alpha Centauri, lies 4.2 light‑years away and comprises three stars—Alpha Centauri A, B, and the faint Proxima Centauri. Two confirmed planets orbit Proxima Centauri, and a handful of additional candidates orbit Alpha Centauri B, offering a glimpse into the diversity of nearby systems.
In 2023, astronomers announced a six‑planet system 100 light‑years away in the constellation Coma Berenices. A collaboration between NASA’s Transiting Exoplanet Survey Satellite (TESS) and the European Space Agency’s CHEOPS mission revealed an “in‑sync” system in which the planets orbit their star in a resonant configuration—a rare cosmic architecture that further demonstrates the variety of planetary systems in our galaxy.
sripfoto/Shutterstock
One of the biggest obstacles to cataloguing solar systems is simply the size of the Milky Way. If the majority of its 100‑to‑400 billion stars host planets, the galaxy could contain billions of planetary systems. Yet to date, astronomers have confirmed just over 5,000 stars with orbiting planets, a minuscule fraction of the total.
Mapping even a small swath of the galaxy is an enormous task, given its density of stars, planets, asteroids, and dark remnants like black holes. The sheer volume of data required, coupled with limited observational resources, means that a comprehensive census of solar systems will likely remain a long‑term goal.
Nazarii_Neshcherenskyi/Shutterstock
Stars are bright, making it challenging to spot the faint light reflected or blocked by orbiting planets—especially when those stars lie thousands of light‑years away. Our solar system sits in the Orion‑Cygnus arm of the Milky Way, a region that offers a relatively clear view of nearby stars but still makes the identification of distant planets a formidable task.
It wasn’t until 1992 that astronomers Aleksander Wolszczan and Dale Frail used the Arecibo radio telescope to confirm the first exoplanets orbiting the pulsar PSR B1257+12, located 2,300 light‑years from Earth. Three years later, graduate student Didier Queloz and Michel Mayor announced the discovery of 51 Pegasi b, the first planet found orbiting a Sun‑like star. These breakthroughs opened the door to a new era of exoplanet science.
Dennis Sonne / 500px/Getty Images
While a definitive count of solar systems remains out of reach, NASA’s missions have dramatically expanded our inventory. The Kepler space telescope, launched on March 6, 2009, pioneered the search for Earth‑size planets around other stars. In 2010, Kepler announced the discovery of Kepler‑9, the first multi‑planet system identified by the mission.
Over its nine‑year mission, Kepler revealed that the Milky Way hosts billions of exoplanets—more than there are stars. To date, NASA has catalogued over 7,400 confirmed exoplanets in more than 5,000 planetary systems, with ongoing studies targeting rare worlds that challenge our understanding of planetary formation.
Because the number of known systems is continually updated as new observations come in, the total count of solar systems in the Milky Way remains an elusive figure—at least for now.
