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Wednesday 9 October 2013

Pluto's New Horizons

[EDIT - June 2014] This article is now also available as a video, thanks to a group of media students at Sheffield Hallam University who created an animated version of our article. For more information, read about how we partner with universities to create videos.

“Pluto is dead”, according to Mike Brown (in How I Killed Pluto and Why it Had it Coming), but that doesn’t mean we shouldn’t go there. In fact, this is one of the reasons why we are going there. Unsurprisingly, given the distances involved, we know very little about Pluto (“You may think it’s a long way to the shops, but that’s just peanuts to space,” to quote Douglas Adams in The Hitchhiker’s Guide to the Galaxy).

Photograph of Pluto taken with Hubble Space Telescope
We're used to seeing detailed pictures of our neighbouring planets like Mars, but this is the best image we have of Pluto - taken by the Hubble Space Telescope in 1994. So what does Pluto really look like? Image credit: NASA/HST

Discovered in 1930, Pluto remains something of a mystery, as astronomers are a long way from understanding its origin. Pluto is one of many rocky and icy bodies which form the Kuiper Belt, in the outer region of the solar system. Pluto was discovered by Clyde Tombaugh in a systematic search for a planet beyond Neptune. Its high surface reflectivity initially made it appear larger than it actually is. Pluto was initially considered as a planet, before the International Astronomical Union officially defined what a planet was. At one point Pluto was thought to be a rogue moon of Neptune.

Is this what the surface of Pluto looks like? Image credit: ESO/L. Cal├žada

Photograph of Pluto and its moons Charon, Nix and Hydra taken by the Hubble Space Telescope
This Hubble image shows four of the moons we know Pluto has - but are there any more? Image credit: NASA
Much of the information we have been able to determine about Pluto is based upon high-res images taken by Hubble Space Telescope (the image above, courtesy of Wikipedia, was a computer generated landscape of the plutoid’s surface using CRIRES software). An example of this is how one of Pluto’s moons, Kerberos, has been estimated between 13 and 35km in size, whilst it’s mass or composition are based upon conjecture. It is quite possible that Pluto has rings or moons additional to the five that we have been unable to detect so far.

As part of our ongoing studies of Pluto, NASA launched the robotic spacecraft New Horizons in January 2006, and will be the first spacecraft to study Pluto and its moons. However, New Horizons is not scheduled to arrive at Pluto until July 2015.

Like NASA’s Juno spacecraft described in yesterday’s article by Cian O'Regan, New Horizons has paid a visit to Jupiter. But unlike Juno, New Horizons didn't stop there - it used the gravity of Jupiter to perform a slingshot manoeuvre in exactly the same way as Juno is using the gravity of the Earth today, to gain speed and go further our into the solar system. But scientists have shown that it might be possible to try and detect any signs of the Flyby Anomaly as a result of this visit - though so far, nothing seems to have been published.

The flyby anomaly was first noticed in December 1990, following Galileo’s Earth-flyby. A review of data following this flyby, collected by the Deep Space Network, revealed an unexpected increase in the Doppler residuals when they were expected to remain flat, that corresponded to an increase in velocity of 3.92mm/s. Subsequent investigations have not proven successful in determining the cause of this effect. Because it has only been seen in flybys of the Earth, it is more accurately known as the Earth Flyby Anomaly - but that might change if indeed such an anomaly is also found at Jupiter.

Artist's impression of NASA spacecraft New Horizons
Artist's impression of the New Horizons spacecraft. Image credit: NASA
New Horizons will approach Pluto at tremendous speeds, and unlike Juno it won't have the option of going into orbit around its target. So New Horizons will pay a truly flying visit to Pluto, passing by at a whopping 14km every second. To put the scale of this manoeuvre into perspective: imagine trying to throw a marble such that it skimmed a football 500m away, travelling at 200mph. The level of navigational precision required for this manoeuvre is of Gaussian proportions.

As the New Horizons mission is only a fly-by, the amount of information will be limited, due to the limited time-frame (two weeks) in which NASA can conduct research which will yield viable results. Nonetheless, the core mission objectives for New Horizons are to determine global geology of Pluto and its largest moon Charon, map the chemical compositions of their surfaces, and characterise the atmosphere of Pluto. There's probably more we don't know about Pluto than is that we do.

Following the Pluto-flyby, New Horizons flight path will send it deep into the Kuiper Belt, with planned flybys of Kuiper Belt Objects to acquire the similar data to what it collected whilst passing Pluto.

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This article is by freelance writer Peter Ray Allison, as part of our World Space Week series. Peter has written for a wide range of publications, including BBC Magazine, GamesTM and Prima Parenting. 

With what little spare time he has, Peter can be found gaming, dragging his family to science-fiction conventions, and feigning deafness so he can keep his nose in a book at dinner time. He is also a member of the TWDK advisory board.

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