How many planets are there actually?

How many planets are there? That question seems simple, but the answer depends greatly on how you define ‘planet. Do you say eight, nine or thousands? The answer is both scientifically and culturally interesting, and the discussion about Pluto plays a big part in that. In this blog, we explain how many planets there are in our solar system, which objects are no longer included, and how many worlds have now been discovered outside our solar system.

What is a planet according to science (official definition)

According to the International Astronomical Union (IAU) there are three conditions an object must meet to be a planet:

1. It orbits a star (like our sun).
2. It has enough mass to have a round shape due to gravity.
3. It wiped its orbit around the sun clean of other objects.

Based on that definition, our solar system counts eight official planets:

• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn
• Uranus
• Neptune

What about Pluto?

Until 2006, Pluto was considered the ninth planet. It meets the first two conditions, but not to the third: Pluto shares its orbit with many other objects in the Kuiper Belt: a ring of icy objects at the edge of the solar system. Therefore, Pluto was renamed dwarf planet.

Besides Pluto, there are four other objects officially recognized as dwarf planets:

• Eris
• Haumea
• Makemake
• Ceres (which is in the asteroid belt)

Although dwarf planets are no longer official planets, they are still important to our understanding of the formation of the solar system.

How many planets are there outside our solar system?

In recent decades, we have begun to look far beyond our own solar system. Thanks to telescopes such as Kepler, TESS and James Webb are more than 5,000 exoplanets discovered. These planets orbit other stars in our Milky Way.

Some exoplanets resemble Earth, others are gas giants like Jupiter, and some fall into categories we are not familiar with here, such as ‘super-Earths’ or ‘hot Jupiters.

🔗 Find out more about recent discoveries in our blog on the James Webb Space Telescope

How many are there in total?

Astronomers estimate that our Milky Way alone is hundreds of billions of planets contains. Most have not yet been discovered, but their existence is inferred through:

Gravitational influences on other celestial bodies, transit photometry (light attenuation when passing in front of a star) and radial velocity measurements

What are dwarf planets and asteroids?

In addition to the eight planets and five official dwarf planets, there are thousands of smaller objects, such as asteroids (asteroids) and TNOs (Trans-Neptunian Objects).

Some of these objects are nearly circular and might have received planetary status under a more flexible definition. The discussion about Pluto and the planet definition thus remains topical, especially in educational circles.

What can you see for yourself with a telescope?

You can't observe all the planets with a telescope, but you can observe some of them:

• Jupiter and its moons are visible even with a small telescope.
• Saturn shows its rings as early as 60x magnification.
• Mars is red and recognizable, especially around opposition (opposition is when a planet is closest to Earth)
• Venus exhibits phases, just like the moon.
• Mercury is tricky, but sometimes visible at sunrise or sunset.

🔗 Want to know more? Check out our guide to planetary observation

Pluto is too small and too dim to see with amateur equipment unfortunately... so it falls just outside the boat again.

Conclusion: how many planets are there?

The question “how many planets are there actually?” has several correct answers, depending on your definition:

Clearly, our understanding of planets is dynamic. As we develop new technologies and look further into the universe, these numbers will continue to grow.

Want to know more about which telescope you need to see planets? Read our selection guide for beginners or read a comprehensive blog post about planets in our solar system including photos here.