promise you this, though, we're never going back to nine planets… ever.

When many of us grew up, there were nine planets in the Solar System. It was like a fixed point in our brains.

As kids, memorizing this list was an early right of passage of nerd pride: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

But then in 2005, Mike Brown discovered Eris, an icy object thought to be about the same size as Pluto, out beyond its orbit.

That would bring the total number of planets to ten. Right? There's no turning back, textbooks would need to be changed.

In order to settle the dispute, the International Astronomical Union met in 2006, and argued for, and against Pluto's planethood. Some astronomers advocated widening the number of planets to twelve, including Pluto, its moon Charon, the Asteroid Ceres, and the newly discovered Eris.

In the end, they changed the definition of what makes a planet, and sadly, Pluto doesn't make the cut:

The Solar System[a] is the Sun and the objects that orbit the Sun. These are a planetary system of eight planets[b] and various secondary bodies, dwarf planets and small Solar System objects that orbit the Sun directly,[c] as well as satellites (moons) that orbit many planets and smaller objects. The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant molecular cloud. The vast majority of the system's mass is in the Sun, with most of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, called the gas giants, are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of substances with relatively high melting points (compared with hydrogen and helium), called ices, such as water, ammonia and methane, and are often referred to separately as "ice giants". All planets have almost circular orbits that lie within a nearly flat disc called the ecliptic plane.

The Solar System also contains regions populated by smaller objects.[c] The asteroid belt, which lies between Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, linked