Could our moon be a twin planet? By a new definition of planets, it would be. 

  

Our solar system could be about to get 100 new planets, under a new proposal by a top NASA scientist. 

But don’t worry – there’s not a whole bunch of new worlds flying towards our solar system, preparing to dock next to the sun.

Instead, the whole way we classify planets is wrong – and we should actually consider our moon as a planet, says Alan Stern, principle investigator of Nasa’s New Horizons mission to Pluto.

Stern and five colleagues have written a suggestion of a new way to classify planets – which would no longer require planets to orbit the sun.

If accepted by the International Astronomical Union (IAU), the move would mean that our solar system would acquire 100 new planets – including Saturn’s moon Titan and Jupiter’s moons Europa and Ganymede.

The team says, ‘In the mind of the public, the word ‘planet’ carries a significance lacking in other words used to describe planetary bodies… many members of the public assume that alleged ‘non-planets’ cease to be interesting enough to warrant scientific exploration.’

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Siri tells me a planet is “a celestial body moving in an elliptical orbit around a star.” If a celestial body is any non-man-made object visible in the sky, what about asteroids, comets, and alien obelisks? Obviously Siri’s definition of a planet needs revision.

How many potential planets are there in our solar system? Here’s what we know now:

A solar system is a star and all of the objects that travel around it — planets, moons, asteroids, comets and meteoroids. Most stars host their own planets, so there are likely tens of billions of other solar systems in the Milky Way galaxy alone. Solar systems can also have more than one star. These are called binary star systems if there are two stars, or multi-star systems if there are three or more stars. 

Planets: 8

Dwarf Planets: 5

Moons: Known = 149 | Provisional = 24 | Total = 173

Comets: More than 3,400

Asteroids: More than 715,000

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