How Many Planets in Our Solar System Are There?

 Before Pluto was discovered, there were seven planets in our solar system: the Sun, Earth, Mars, Jupiter, Saturn, Uranus, and Pluto. These were all named after their respective constellations, and before the discovery of Pluto, these planets were all referred to as the ‘primal’ planets. However, there was debate about the status of Pluto, which would have come after the more well-known Neptune. Because Pluto is so far from Earth and has a wildly tilted orbit, astronomers were unsure whether it was a planet.

While we only know of seven planets in our solar system, the discovery of 51 Pegasi b opened a new window into the universe. Astronomers soon found a class of planets orbiting other stars in tight orbits. These planets were dubbed ‘hot Jupiters’ because they orbit their stars with such extreme accuracy that they can be seen by astronomers in a matter of days. Meanwhile, gas giant planets in our solar system are classified as ‘eccentric planets’, which follow circular paths.

The size of a planet determines the number of planets that can fit in their orbits. Jupiter, for instance, has a 10 times larger Hill radii than Earth, meaning that it could fit 10 Earth orbits in its current orbit. Making planets smaller allows us to maximize the number of planets we can observe in our solar system. The more planets we have, the less likely we’ll have to visit them.

Astronomers continue to hunt for the elusive Planet Nine. The Atacama Cosmology Telescope, a six-meter telescope in Chile, recently spotted thousands of candidate sources, but it was unable to confirm any of them. However, the astronomers believe there is a planet at the center of our solar system that might be as large as Earth. These planets have been found to be around five to ten times as large as Pluto. The astronomers estimate that there are more than 200 smaller planets in our solar system.

The outermost planets in our solar system are Mercury and Venus. They orbit the sun in an oval-shaped path and are slightly off-center. The sun has eight planets in our solar system, including the largest, Jupiter, which is 99% hydrogen and helium. Jupiter is home to constant storms and features the Great Red Spot. The planets are surrounded by a thin, but very dense atmosphere.

Scientists accepted Copernicus’ theory of the solar system, and later developed a theory of how planets move around the sun. Eventually, Isaac Newton proved that planets travel around the sun by gravitational attraction. The larger the mass, the stronger the attraction. Hence, the more planets in our solar system, the larger the size of the universe. It was this idea that made scientists ponder the question of how many planets are in our solar system.

Mercury and the moon are the second and third largest planets in our solar system. The moon has a diameter of about two-thirds of Earth’s. Its size is smaller than that of Pluto. The larger Kuiper belt object Makemake is more than two-thirds the size of Pluto, and does not appear to have any moons. Jupiter and Eris are the most massive of all planets, besides Earth, and the moons.