Pluto has long been a source of fascination for science – partly because, at a minimum of 4.4 billion kilometres (2.7 billion miles) at its closest orbital approach to the Sun, it has been beyond the effective reach of all but one spacecraft: Voyager 1. NASA instead opted for a close flyby of Titan (Saturn’s biggest moon), which put it beyond a compatible trajectory for Pluto.
That’s one reason why, in 2006, NASA sent the New Horizons spacecraft off to Pluto tasked with a double-reconnaissance of the dwarf planet and its largest satellite, Charon, as well as an extended mission into the most distant parts of the Solar System to investigate objects in the mysterious Kuiper Belt.
At the time of writing, New Horizons has taken its payload of scientific instruments 25 astronomical units (which is approximately 3.7 billion kilometres/2.3 billion miles) and is scheduled to begin its Pluto flyby in July 2015.
Piggybacking an Atlas V rocket (the same kind used for NASA’s Mars Reconnaissance Orbiter and Mars Science Laboratory) for launch, New Horizons achieved the fastest escape velocity ever at 57,600 kilometres (35,800 miles) per hour, on a trajectory that should see it reach Pluto around July 2015.
New Horizons won’t be landing anywhere or launching a vehicle (like the MSL and Curiosity, for example), so its seven main instruments are primarily designed to scan designated items of interest and answer questions like what Pluto’s gradually depleting atmosphere is comprised of, what the surface of both Pluto and Charon look like and generally what else can be found in the uncharted Kuiper Belt.
Among them, an instrument called ‘Ralph’ will take care of map-making, ‘Alice’ will provide atmospheric data via an ultraviolet spectrometer and REX is primarily responsible for making sure all the data collected is transmitted safely across the five light hours it takes to reach Earth from Pluto.
In the seven years that New Horizons has spent on its journey to Pluto, scientists have discovered potential new hazards to the spacecraft. When New Horizons set off, only three of Pluto’s five satellites were known about: Charon had been discovered in 1978, Nix and Hydra both in 2005. Since then, the Hubble telescope has spotted two more, known simply as P4 and P5. The prospect of finding additional satellites before New Horizons arrives makes calculating a safe orbit of Pluto more complicated in itself, but these new moons are known as ‘debris generators’, filling Pluto’s orbit with material they have drawn in from the Kuiper Belt. A particle the size of a sand grain can potentially destroy this spacecraft travelling at such a high velocity. To deal with this, NASA is making multiple contingencies to avoid these debris zones as well as plotting a ‘bail-out trajectory’ to take New Horizons to safety.
Exploring the Kuiper Belt
The three main zones our Solar System is divided into are the inner Solar System (characterised by the rocky planets of Mercury, Venus, Earth and Mars), the outer Solar System (typified by the gas giants Jupiter, Saturn, Uranus and Neptune), then the Kuiper Belt. Pluto and other icy dwarf planets inhabit this zone, within which 1,000 different objects have been discovered and 100,000 KBOs (Kuiper Belt objects) with diameters in excess of 100 kilometres (62 miles) are estimated to exist.
Many short-period icy comets (those with orbital periods of less than 200 years) are thought to have originated from the Kuiper Belt, including the space rock that is suspected to have made the Chicxulub impact that triggered the dinosaur-slaying mass-extinction event 65.5 million years ago. We have very little knowledge of the Kuiper Belt and hope to get a better picture of how the Solar System formed once New Horizons has investigated it.