However as New Horizons, which will be the fastest spacecraft launched, prepares to hurtle towards the planet at 100 times the speed of a jet plane, all that is about to change.
New Horizons is being sent to Pluto to explore the Kuiper Belt, a mysterious region beyond Neptune, believed to hold thousands of comets and icy planetary objects that make up a third zone of the solar system, the rocky and gaseous planets making up the other two.
The 2.1 metre tall craft is due to liftoff on Tuesday. Its incredible speed means it is expected to cruise past the moon in just nine hours, Jupiter in a little over a year and reach Pluto – five billion kilometres away – in nine years.
When it reaches Jupiter in 13 months, it will use the giant planet’s gravity to create a slingshot effect as a slingshot reducing the journey time to Pluto by five years.
Since its discovery in 1930, there have been many suggestions that Pluto is not even a planet at all. Its icy make-up distinguishes it from rocky bodies such as Earth or Mars and the giant gaseous planets including Jupiter.
New Horizons will be the fastest spacecraft launched, travelling nearly 100 times the speed of a jetliner. It should reach Earth’s moon in nine hours, Jupiter in 13 months and Pluto in nine years.
Nasa’s first space probe to Pluto will use radioactive plutonium pellets to power much of its journey, and is seeing protests against it.
The plutonium pellets will produce less energy than two 100-watt lightbulbs.
Once the piano-sized probe reaches Jupiter, it will use that huge planet as a slingshot for an added boost to the outer edge of the solar system.
Pluto was discovered in 1930 by the astronomer Clyde Tombaugh in Arizona. It is the smallest planet in the solar system and the only planet classified as an “ice dwarf.” It has three moons.
Pluto is located in the Kuiper Belt, a mysterious region that lies beyond Neptune at the outer limits of the planetary system. Scientists believe the Kuiper Belt holds clues as to how the outer solar system was formed.
However, in recent years astronomers have discovered that ice dwarfs are in fact the most populous planetary group in the solar system.
Now, scientists believe learning more about a group previously considered something of an anomaly will reveal valuable insights into the origins of the planetary system.
Alan Stern of the Southwest Research Institute in Boulder, Colorado, the mission’s principal investigator, says: “Just as a Chihuahua is still a dog, these ice dwarfs are still planetary bodies. The misfit becomes the average. The Pluto-like objects are more typical in our solar system than the nearby planets we first knew.”
New Horizons is expected to reach Pluto as early as 2015 when the spacecraft will study the planet’s large moon, Charon, as well as two other satellites that were discovered last year.
Window back in time
The $700 million mission should provide scientists with a better understanding of the Kuiper Belt, and they say they can learn about the evolution of the solar system as the belt contains debris left over from the formation of the outer solar system.
“It provides for us a window 4½ billion years back in time to observe the formation conditions of giant planets,” Stern said. “This is a little bit about rewriting the textbooks about the outer planets.”
A successful mission to Pluto will complete a survey of the planets by unmanned spacecraft that Nasa began in the early 1960s with the Mariner programme’s exploration of Mars, Mercury and Venus.
The best images of Pluto currently come from the Hubble Space Telescope, but they suffer from low-resolution fuzziness.
The 474.3kg piano-sized spacecraft will be launched on an Atlas V, one of the largest rockets at Nasa’s disposal.
The rocket’s makers, Lockheed Martin, experienced problems on another Atlas propellant tank similar to the one being flown to Pluto, forcing a delay of New Horizons’ launch by several days to give the contractor extra time for inspection.
During the trip between Jupiter and Pluto, the probe will go into hibernation, meaning most of its systems close down to conserve power. It will send weekly “beeps” back to Earth, providing updates on the vehicle’s condition.
If the spacecraft is unable to launch during the month-long window that closes on 14 February, the next opportunity is in February 2007. But that would push back an arrival at Pluto to 2020 since New Horizons would not be able to get the gravity assist from Jupiter then.
New Horizons will send ‘beeps’
Powered by nuclear fuel that will produce less energy than is used by two 100-watt lightbulbs, New Horizons is loaded with seven instruments that will be able to photograph the surfaces of Pluto and Charon and examine Pluto’s atmospheric composition and structure.
Two of the cameras, Alice and Ralph, are named after the bickering couple from television’s “The Honeymooners.”
The spacecraft has a thermos-bottle design that will allow it to stay at room temperature. Tucked inside the probe will be a US flag and a CD containing about a half million names of ordinary citizens who signed up on a Nasa website.
Pluto and the Kuiper Belt have revealed several surprises to scientists in the past few years.
In 2001, it was discovered that binary objects – pairs like Pluto and Charon – litter the belt, and a year later they learned that Pluto’s atmosphere undergoes rapid and dramatic global change.
Last summer, scientists then discovered Pluto’s two other moons.
Scientists expect more unexpected discoveries from the New Horizons mission.
Stern says: “You can see why we think it’s going to be like kids in a candy shop.”