[attach id=554626 size="medium"][/attach]

What really is a planet? Our solar system is host to thousands of objects ranging from planets to asteroids to comets, and many others. In recent years, however, there’s been a focus on how many planets the solar system contains, eight or nine?

On August 24, 2006 the International Astronomical Union reached a verdict that the solar system has eight planets and that Pluto wasn’t one of them. Pluto was relegated to the category of dwarf planet since it only satisfies two out of the three requirements for an object to be a fully fledged planet. These are, firstly that the object must be in an orbit about the sun, unlike the moon for instance. Secondly, the object must have a strong enough gravitational pull to give a rounded shape to its surface.

This is called hydrostatic equilibrium and essentially means that the object is dominated by its own gravity and not by other objects or the particular circumstances of its creation. Lastly, and for Pluto crucially, the object in question must have cleared its orbital neighbourhood of dominant objects like asteroids and so on.

Planetary orbits are littered with asteroids and other small objects, which is a safety concern for space missions. However, these objects are normally very small in comparison with the planet in question. For instance in our case, earth makes up 1.7 million times the mass of the objects around it while in the case of Pluto this ratio drops to roughly 0.07. The reason behind this isn’t Pluto’s size, it’s its position in the solar system. Pluto is found in what’s called the Kuiper belt, which is a disc region outside the orbit of Neptune where asteroids and comets are found in much larger numbers than the planetary part of the solar system.

In all likelihood there are hundreds of these dwarf planet objects. Five have been accepted as such and have been characterised but there is clearly a lot more we don’t yet know about the solar system we live in and much more research needs to be done.

Find more myths debunked at http://www.iflscience.com/