To the 9th rock

The fastest spaceship built by man is en route to the farthest, coldest planet in the Solar System. Nasa?s New Horizons mission to Pluto reached the Moon just nine hours after launch last Thursday and will swing by Jupiter early next year, using the giant planet?s gravity to catapult it towards Pluto.

The fastest spaceship built by man is en route to the farthest, coldest planet in the Solar System. Nasa’s New Horizons mission to Pluto reached the Moon just nine hours after launch last Thursday and will swing by Jupiter early next year, using the giant planet’s gravity to catapult it towards Pluto. When it gets to Pluto — the only planet in the Solar System that a spacecraft hasn’t directly observed — in mid-2015, it will map a surface so cold that gases like nitrogen, methane, and carbon dioxide freeze solid, resulting in a surreal landscape.

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The Moon is larger than Pluto. Although Pluto’s wild swing around the Sun periodically carries it inside Neptune’s orbit, it’s still so far that, even with the best telescope, trying to see its surface features is like trying to spot a cricket ball’s seam from 55 miles away.

Pluto belongs to a planetary group called ‘ice dwarfs’ that graze in the Kuiper Belt billions of miles from the Sun. Since this region is also home to thousands of small icy objects called Kuiper Belt objects (KBOs), some astronomers suggest that Pluto is a KBO. It’s too small to be a planet, they argue, and its elongated orbit and odd orbital plane make it behave more like a KBO. Apart from disappointing generations of schoolchildren who grew up on Solar System charts depicting Pluto as the ‘littlest’ planet, this is a question of semantics. For Pluto is big enough for gravity to give it a round shape like any planet (and unlike KBOs that tend to be misshapen). It revolves around the Sun like other planets, and also has an atmosphere and seasons. So the question should be what Pluto is like, not what it is.

Astronomers can learn a lot about the evolution of the Solar System by studying distant Pluto and the Kuiper Belt that contain debris left over from its formation. This is a unique window for peering 4.5 billion years back in time to ‘see’ how material interacted in the infant solar system to form planets.

The more we discover about the outer planets, the more we get to know about how Earth and the inner Solar System were formed. It’s like reading a mystery novel where something new is known every time you turn the page, but the story remains incomplete until you finish the book.