Eight months after Philae landed on a comet, and four months after Dawn went into orbit around Ceres, space history is once again about to be made. Today, having travelled for nine and a half years, and over three billion miles, the New Horizons probe will make its closest approach to Pluto – the first spacecraft ever to visit what was once the ninth planet.
It’s not going to be quite the same as the tension of the Philae landing. Like Philae, New Horizons is much too far away from Earth for manual control to provide any meaningful assistance, but it won’t be going into orbit: it’ll just perform an automated sequence of observations as it flies by. And after that, it will take months to send all the data back across those billions of miles to Earth.
These days, Pluto may technically be classified as a dwarf planet – thus messing up the ‘my very easy method just speeds up naming planets’ mnemonic – but ultimately, ‘planet’ and ‘dwarf planet’ are just words created by people because we like to categorise. Calling Pluto by a different name doesn’t change anything about Pluto itself. It’s a rocky sphere orbiting the Sun, usually but not always further away than Neptune, which we had never seen up close before until this year. Pluto perfectly demonstrates how little we know about the Solar System as we get further away from the Sun. It wasn’t known to have a moon until 1978, forty-eight years after its initial discovery. And between 2005 and 2012, it was found to have four additional moons!
The space books of our childhood, which called Pluto the ninth planet, also said that no probe had ever visited it – and that is officially no longer true. Thanks to the pictures coming back from New Horizons, Pluto is now more than just a speck on astronomical photographs: it’s a real, detailed world, with craters and chasms and whale-shaped dark patches. We don’t have to imagine exactly what it looks like anymore. Another gap in our knowledge is being filled in; another unknown territory explored.
So yes, what’s happening today is pretty brilliant.
Check out the official New Horizons website here.
RJ's Blog 
I’m still confused about the planet/ not planet thing (thought planet was body orbiting sun/ star, whilst satellite/ moon orbits a planet)? Has been a long while since I did science!
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That is indeed what separates planets from satellites, Angela. As for what makes Pluto an un-planet, that’s quite messy: astronomers are still arguing about it now.
For years, many astronomers weren’t comfortable calling Pluto a planet because it’s so unlike the gas giants that are its closest neighbours: it’s smaller than Mercury, and its orbit sometimes goes inside Neptune’s. Then in the early 21st century, other objects similar to Pluto were discovered in the area beyond Neptune known as the Kuiper Belt. So either all of these objects had to be called planets as well, or they and Pluto had to be put in a separate category. So really, it was all done in the name of being as neat as possible. Officially, Pluto is now not a planet because a planet is considered an object big enough to clear out any smaller objects within its orbit – but many astronomers think this definition is a bit iffy as Earth is a planet and yet is still surrounded by asteroids.
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thanks for the explaination Richard. Seems it’s always the way with science that stuff that’s stated as fact on a basic level becomes fuzzy the moment you start delving.
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