Derby and District Astronomical Society

Aries
The Journal of the Derby and District Astronomical Society
January - April 2006
[Contents]

Editorial

Aries January-April 2006 Welcome to this edition of Aries!

So here we are again, and what does the 2006 have in store for us? Well the front cover for this edition of Aries should give you a clue. As I write this editorial, we are a little over two weeks to the launch of one of the most ambitious space missions ever conceived of. On January 17th 2006 the New Horizons spacecraft will start its long journey into history, its destination, that frozen outpost of the Solar System, Pluto. At long last we have a spacecraft that is going to investigate that mysterious and chilly body.

New Horizons will conduct a fly-by investigation of Pluto. The spacecraft will have to get to its destination fast, for it is engaged in a race against time. It is hoped to get New Horizons to Pluto before that bodyís tenuous atmosphere freezes out as Pluto begins to recede from the Sun in its orbit. For that to happen, New Horizons will be literally flung out of the warm heart of the Solar System towards Pluto, which means that the spacecraft will not be slowing down, hence the Pluto fly-by. But the mission does not stop there, New Horizons will carry on, it is hoped to send New Horizons on to encounters with at least two Kuiper Belt Objects (KBOs), the class of objects to which it is thought that Pluto belongs to. To my mind the New Horizons mission marks the end of the first phase of the exploration of the Solar System, what the second phase of Solar System exploration will reveal is anyoneís guess, nor would I even try to do so.

The New Horizons mission will not be a short one. It will take the spacecraft nine years to traverse the Solar System to get to Pluto. The Pluto encounter is scheduled to take place in 2015. To aid New Horizons in its journey to this frozen world, the giant of the Solar System, Jupiter, will lend a hand. New Horizons will fly by Jupiter and get a velocity 'boost' courtesy of the giant planetís gravitational field. But that is not to say that New Horizons is a 'slow' spacecraft. New Horizons will be launched atop an Atlas V heavy lift launch vehicle that will throw the spacecraft out of the gravity well of the Earth and onto the first leg of its journey. New Horizons is also quite a small spacecraft, definitely not a 'monster' probe like Cassini/Huygens, so being that New Horizons is so small, it is also a very light spacecraft. The Atlas V will impart quite a considerable amount of energy to New Horizons in the very early stages of its journey. In addition to this, to help New Horizons get to Jupiter, a Centaur upper stage will give New Horizons additional velocity. To give you some idea of how much velocity the Atlas V and the Centaur upper stage combination will give to New Horizons, it took the Apollo astronauts about four days to reach the Moon, New Horizons will pass the orbit of the Moon on the evening of its launch day! Furthermore, it took the Galileo spacecraft six years to get to Jupiter and Cassini/Huygens took four years to pass that gas giant. New Horizons, on a more direct route, will pass the orbit of Jupiter in thirteen months! This little spacecraft is really screaming out of the inner Solar System to get to Pluto.

So, why go to Pluto and the Kuiper Belt? Well, first off, letís go there simply because Pluto is there! It is the last 'planet' to be visited by a spacecraft. Pluto is one of the last unknown 'major' bodies of the Solar System, so it is just crying out to be explored. Also Pluto and its Kuiper Belt cousins represent the 'primitive' Solar System. When New Horizons encounters Pluto it will be, in a sense, travelling back in time to the Solar Systemís early history. Pluto and the Kuiper Belt Objects are the frozen 'builderís rubble' left over from the formation of the Solar System. These bodies could tell us more about our origins than any other Solar System object, apart from comets of course. Also, New Horizons may finally settle the argument that is currently raging amongst astronomers as to Plutoís true status - can it really keep its place as a planet in the light of recent discoveries?

Personally, and I know I may be holding a controversial viewpoint on this - I regard Pluto to be nothing more than a relatively close-in KBO. Now I know some people would disagree with me on this, but hear me out on this one. What actually constitutes a planet? Size? Possession of an atmosphere? Well, Plutoís got one, thin as it may be and only temporary while it is close to the Sun in its 248-year orbit. How about the possession of moons, well, again, Pluto has one, whoa, wait a minute, wrong! Pluto now has three moons (see Astro News Desk item)! Well what does constitute a planet, at this point no one knows and astronomers are debating that very issue. But to me Pluto is a large KBO, mainly due to its position in the Solar System, possibly captured into its present orbit by Neptune, and recently, we have found KBOs larger than Pluto. So if you push size as a marker of 'planethood' then Pluto loses out on this one. It is theorised that there could be out there in the Kuiper Belt a KBO about the size of Mars. Now, do you call that potential body a planet?

Finally, on a more personal note, this mission will hold some personal significance for me. Myself and 403,000 other people submitted their names via the New Horizons website. These names were placed onto a CD-ROM that was, in turn, attached to the New Horizons spacecraft. So in a very real sense I will be going to Pluto as well, I donít know how many other DDAS members have signed up for this trip, but I do hope I will have some familiar shipmates to come along on the journey with me. So a part of me is heading out into the cold unknown of the extreme outer Solar System, but I will be in good company for as well as having 435,000 other people with me, Iím sure that the spirit of Plutoís discoverer, Clyde Tombaugh, will be along for the ride as well and what better guide to have with you on such a voyage.

Talking about names, not only is mine heading out to Pluto hopefully on the 17th January, but also on the 15th January it is coming back! The Stardust probe will be coming home after a seven year, 2.88 billion mile round trip journey to collect cosmic dust particles and cometary particle material from Comet Wild-2. 1.8 million other peopleís names and mine are on two microchips, one on the Stardust spacecraft proper, which stays in space and the other is on the sample return capsule. The sample return capsule is due to return to Earth in the early hours (local time) in the Utah Desert, USA on January 15th. The Stardust spacecraft itself, after releasing the sample return capsule, will fly past the Earth and go into an orbit about the Sun, and will stay there if it is not ejected out of the Solar System by some gravitational close shave. Either way, my name will stay in space for quite some time to come! Boy! Do I know how to get around or what?

So, whatís in this issue of Aries then? We have the usual Society News roundup and Astro News Desk for this edition. I tried to keep the number of stories down but there were so many interesting stories around during the past three months that I found it a very difficult task to pick out the best of the best. We have the first appearance of the Letters to the Editor page, thanks to David Selfe for his contribution.

We have three very good articles for this edition of Aries. The first is by Malcolm Neal and concerns itself with solar eclipses. David Selfe has been hard at work at the keyboard and has produced the first part of his A History of the Solar System series, if the first part is anything to go by, this will be a very good series of articles. I was going to publish the first part of my 'Mining the Sky' series, but due to the impending launch of the New Horizons spacecraft on January 17th, I decided to hold it over until the next edition of Aries, so instead I have produced a 'short' article outlining the New Horizons mission.

Finally, we have the return of the Astro Crossword thanks to Dave Selfe for submitting it. The answers will appear in the next edition of Aries.

Anthony Southwell So enjoy this edition of Aries and onward to Pluto!



Editor

December 2005


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