New Horizons to Pluto

When Percival Lowell began the search for “Planet X” little did he know the countless arguments he would cause and effectively how these would lead to a seemingly ever changing solar system. “Planet X” was not the believed birthplace of the X-Men for anyone hoping for the possibility of super human mutants existing, but rather Lowell’s (incorrect) belief that there was an elusive planet that was responsible for the irregularities in the orbits of both Uranus and Neptune. He was right, there was another planet but it had too small a gravitational pull to affect the two gas giants and it would be over 10 years after this death when it was discovered. In February 1930, Clyde Tombaugh, an observing assistant at Lowell Observatory, was planet hunting in the constellation of Gemini when he found “Planet X”, or what it became known as, Pluto, the only planet to be named by a child!


Artist's concept of New Horizons spacecraft at Pluto (Image credit:NASA)

Artist’s concept of New Horizons spacecraft at Pluto (Image credit:NASA)


Whenever the announcement of a new planet being discovered billions of kilometres from earth was announced in the papers, a young girl named Venetia Burney suggested Pluto would be a good name to her grandfather who had been pondering what they would call it and the rest was down to a proud grandfather and history!  Pluto believed to be in Greek and Roman mythology another name for Hades, the God of the Underworld was in keeping with the mythological names of the other planets.  This strange and cold world has much of its mysteries still intact and for years astronomers and scientists tried to learn as much as they could about this distant world.

When it was first discovered it became widely accepted as a planet despite its miniature size, which is 30 times smaller than our smallest planet Mercury and for decades children were taught many rhymes to remember the ‘nine’ planets in the Solar system. But its life alongside the other planets was not to be a long one.  It began with the first discoveries of TNO’s or Trans-Neptunian Objects. These where objects floating around in the area known as the Trans-Neptunian region, beyond the planet Neptune. There has been over 1000 known TNO’S discovered since the first in  1992 and so with son many being found, the days of Pluto being the largest body beyond Neptune were numbered!

And it was the 21st October 2003 when Mike Brown (who has actually wrote a book called How I killed Pluto and Why it had it coming) and David Rabinowitz were using  a telescope at the Palomar Observatory in the US when they discovered another very cold world at the edge of the solar system that was 2500km across. This was named 2003 UB313 but would later be known as the large dwarf planet Eris. And herein lay Pluto’s fate. With something bigger than Pluto now within our knowledge of space and so many TNOs discovered, what really defined a planet?

Ultimately there where many debates across the world which involved scientists, astronomers, historians, educators and many other professions, but poor Pluto’s demise was fated.  A new definition for planets was put to members of the IAU in August 2006 and it was accepted. So from that bitter-sweet day, the definition for planets is as follows:

“A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.”

Poor Pluto was no more a planet, but instead, to soften the blow it was giving a whole new class. It was now a dwarf planet and really the first of its kind and so the class was given the name Plutoids, probably to try and nurse the wounds of the defeated ‘planet’ Pluto enthusiasts.

On 19 January 2006, before this planetary drama was being resolved, scientists at NASA sent the New Horizons space craft into space on top of an Atlas V rocket, bound for what they believed to be the furthest out planet in our solar system.  But alas, what began as a planet bound mission became a less grand endeavour when Pluto lost its planetary status. But as they say in show business, ‘the show must go on!’ Yes, New Horizons began its mission trying to discover more about a frozen planet in the outer regions of the solar system and that is what it will do, except now it’s a frozen dwarf planet. But New Horizons is still going to be making history and in less than a year it will hopefully be revealing the secrets of the icy Plutoid. But like many things that seemed a long time a away, time has really crept up on the New Horizon scientists and with less than a year to go, they still have much to decide upon. Yes it will reach the outer regions of the solar system and hopefully reveal some amazing images and secrets of Pluto, but where and what should it go to after.

Three faces of Pluto, based on A photomap of Dithering image based on pictures of Pluto from 2002 to 2003 taken by the Advance Camera for Survey of the Hubble telescope. (Image credit: NASA, ESA, and M. Buie (Southwest Research Institute))

Three faces of Pluto, based on a photomap of Dithering image based on pictures of Pluto from 2002 to 2003 taken by the Advance Camera for Survey of the Hubble telescope. (Image credit: NASA, ESA, and M. Buie (Southwest Research Institute))


The New Horizons mission was a multi-layered endeavour, not only is it to try and show us Pluto as we have never seen it before, but also reveal more about those mysterious Kuiper Belt Objects (KBO’s) in the Trans-Neptunian region.  A KBO has never been seen up close before and would we all not like a to see and find out about those mysterious icy bodies left over after the formation of our Solar System 4.6 billion years ago. This has been a huge part of the New Horizons mission and with time running out and ground base telescopes finding major problems trying to identify a suitable target, a true space legend has been called into play. The Hubble space telescope may be pushing on in years but it still as remarkable as ever. With more scientists across the world applying for time on with the space telescope than there is time in the year it is extremely difficult to secure time with the Hubble but thankfully the New Horizons scientists have won some time with the space icon, and boy do they need it. To try and pick an object out from the Kuiper Belt to be the next target for New Horizons is going to be tough. The Kuiper Belt is an area that stretches nearly 8 billion km (5 billion miles) out from the Sun with thousands of icy bodies, some 100 km or more in diameter orbiting around our star.  They need to pick something relatively bright and wide, difficult considering KBOs  roughly measure the size of Manhattan and have tarry surfaces usually darker than charcoal so despite the immense capabilities of Hubble, this will be a toughie for the space telescope but no doubt it will be up to the challenge!

They plan to point to Hubble in the direction of the constellation Sagittarius  and have it move at the same predicted rate of the KBOs so that the stars in the background will obviously streak across the image and the KBOs will be revealed. From here they shall hopefully be able to pick a few bright KBOs that could be the future target of New Horizon’s, so fingers crossed there may be a few bright enough to work with.

As said, New Horizon’s began its mission as a planet hunter and although they may have slightly altered in name it still has not changed how important and ground breaking its mission is. We are already getting images of the icy dwarf planet and its moon Charon as we have never seen them before and we still have just under a year before it reaches its closest approach. As well as that we will hopefully get much more of a glimpse of those mysterious objects beyond and hopefully have more answers to the how and whys of our solar system!

To keep you up to date with this pioneering mission click this link.

(Article by Kerry Scullion, Education Support Officer)