Wednesday 20 July 2011

The Fourth Moon of Pluto

It was recently announced that a fourth moon of Pluto has been discovered. In these heady days of sky-watching, it has become a surprisingly common thing to read – a new moon, dwarf planet, stars – but I recall in my youth being quite certain of the number and names of all the moons in our solar system.

As a child, I distinctly recall being inordinately pleased with myself for remembering the names and order of Jupiter’s sixteen moons. Three had recently been discovered, and then all was quiet for twenty years. It was a strange thing to discover that our local universe, which we had believed to for so long to have been mapped quite successfully, could conceal not merely surprises, but quite literally dozens of them.

We know now that Jupiter has at least sixty-four moons, and that, including IAU-approved dwarf planets, there are at least thirteen major objects in orbit around our sun. Recent findings have, of course, made astronomers much more reticent to assert numbers, or even upper limits. It is possible, in fact, that our solar system – stretching from the sun to the reaches of the Oort cloud nearly a light year away – could contain several thousand planets, dwarf or otherwise.

How can these enormous objects be concealed, we might ask – but the answer is all too simple: an object the size even of the sun would be a mere pinprick of light from the system’s edge, much as are the stars we see at night. If, at that distance, we struggle to perceive an orb of such luminosity, what chance do we have to see a planet so far away, and so concealed by the dust and asteroids of the Kuiper belt?

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