In January 2006 NASA launched a spacecraft that would spend the next nine and a half years sailing through the Solar System. It’s currently travelling at over 70,000km per hour, the fastest spacecraft ever launched. In one month, on July 14, New Horizons will make its closest approach to Pluto.
Pluto was once considered a planet, but as we looked further into the outer regions of the Solar System we began to find more and more objects that were very similar to Pluto. Space scientists met to discuss a formal definition of a planet and as a result Pluto and the other objects were no longer deemed to be planets. Instead, Pluto was classified as a dwarf planet; it is the second-largest such dwarf planet (the largest is Eris), and is the largest Kuiper Belt Object. The Kuiper Belt is a ring that surrounds the inner part of the Solar System, and is comprised of lots of dwarf and minor planets.
Even before we changed the classification of planets, we knew for a long time that Pluto was quite unusual. In one sense, it’s actually a binary object: its largest moon, Charon, is so big compared to Pluto that the two objects orbit around each other, rather than the more common case of a small moon orbiting a much larger planet. Until 2005 we thought Charon was its only moon; in that year the Hubble Space Telescope discovered Nix and Hydra, and in 2011 and 2012 it found Kerberos and Styx, respectively.
When New Horizons launched, we didn’t even know of the existence of some of these moons of Pluto. Will the spacecraft now go on to discover even more of them? Whatever happens, the mission is sure to find more interesting things about the dwarf planet: some of its mission goals include finding out what Pluto and Charon are made of, seeing if Pluto has an atmosphere, measure its temperature, and find out if Pluto has a ring system.
It doesn’t end there, however. Once New Horizons has finished its work at Pluto and beamed new data and discoveries to scientists on Earth, it will go on to travel into even more distant regions of the Solar System. New Horizons will undertake studies of one or two as yet undetermined Kuiper Belt Objects that reside in the depths of space.
Following its main mission objectives, New Horizons will not stop moving. It will continue to travel away from the Sun and its Solar System, eventually arriving at the heliosheath – the shock front created by winds blasting from the Sun impacting on material in deep space and on winds from other stars. If it passes through and exits from this turbulent region, which would happen in about 2047, it will effectively become an interstellar spacecraft, just like Voyager 1 before it.
Late last year the lander Philae became the first craft to land on a comet, and this year Dawn arrived at the minor planet (and largest asteroid) Ceres. With Pluto being our next port of call in July 2015, it’s very clear that we live in very exciting times for the exploration of space and our Solar System.