On Tuesday, NASA's New Horizon's space ship will get its closest look at Pluto after a nine and a half year trek. That's a 4.7 billion kilometre drive. Give or take.

You remember Pluto. It used to be a planet but now it's not.

The trip includes a 30-minute flyby to the far edge of our solar system. And New Horizon will be taking pictures from about 12,500 kilometres away from Pluto. We're expecting the clearest ever clear, colour images of the icy object.

McMaster University astronomer Rob Cockcroft will be watching closely. He knows, more than most, about Pluto.

"We will never have another opportunity to freshly explore an object that was once considered a planet – not until we figure out how to get to extrasolar planets, anyway," Cockcroft says. "The data New Horizons gathers won't just help us understand how Pluto was formed, but how the Solar System itself was formed."

Here's a list of six very cool things Cockroft knows about Pluto that you should know too:

  • Day length: Pluto takes much longer to complete a full rotation than Earth does, making a day there equal to nearly six and half Earth days. A Pluto year is about 248 Earth years.

  • Composition: Basically, Pluto is a huge chunk of rock covered in a relatively thin layer of ice, with nitrogen ice on the surface - and very possibly, water ice between that and the rock.
  • Atmosphere: Pluto doesn't have an atmosphere like ours. It's about 100,000 times less dense than ours, because the planet is "sweating". It's mostly nitrogen, with traces of methane and carbon dioxide, that sublimate – or move from solids directly to gases – off the surface to produce this thin "atmosphere".
    Rob Cockcroft

    McMaster University astronomer Rob Cockcroft. (Jon Evans/McMaster University)

  • Distance: On average, Pluto is about 40 times further from the Sun than the Earth (it varies between 30 and 49 times because its orbit is elliptical). That's between 4.4 and 7.4 billion kilometres from the Sun.
  • Seasons: Pluto's seasons are extreme and long. Earth's seasons are caused by its tilt (23.5 degrees). To give you some perspective, Pluto's tilt is 120 degrees!
  • Orbit: Pluto and its largest moon, Charon, orbit in such a way that the same moon face is always seen from Pluto's surface – just like Earth and its Moon. But Charon is also always in the same spot in Pluto's sky, meaning that if you're on the wrong side of Pluto, you'd never see the moon.