Wednesday, 9 November 2011


I wonder if all my posts from now on could have pertinant headings that happen to be video game titles. Probably not, unless I start blogging heavily about gaming. Still, it's a challenge. What this post is actually about is the huge asteroid that flew past the Earth last night. You may have seen something about it in the news, although there hasn't been a huge amount of coverage. Perhaps this isn't too suprising. The asteroid is invisible to the naked eye, and doesn't have a proper name, merely a number - 2005 YU55. Invisible rocks without names are a harder sell than the more obvious, in-your-face type event, like a nice, shiny comet (remember Hale-Bopp?)

In spite of its apparent obscurity, 2005 YU55 is pretty noteworthy. A C-Type asteroid - essentially a big, black boulder - it's about 400 metres across, and came within spitting distance hitting the Earth. The official classification for something like this is a 'Potentially Hazardous Object.' YU55 has an orbit that takes it through our own, passing even closer to us than the Moon. Sadly, the proximity and size of the rock aren't sufficient to allow us to see it without optical aid. A good pair of binoculars would have been sufficient on a dark enough night, but the Moon's brightness was too much and whited it out. Without a fairly wide-apertured optical telescope it remained invisible, although the radio astronomy boys have reportedly got some excellent readings from it. It's all academic for me, anyway - it was cloudy down my way, as usual.

We're assured that there was never any risk of YU55 hitting the Earth. If it had, it would have been pretty damned serious. An impact on land would have left a four mile wide crater and triggered a mag 7 earthquake. An impact in the ocean would have caused gigantic tsunamis. Not an extinction event, but something to be glad we've avoided. Nonetheless, 200,000 miles is shiveringly close in astronomical terms. A narrow squeak.

Mind you, it's got to come back through yet. It should swing back round the sun and past Venus in eighteen years time. Where it goes from there depends on exactly how Venus' gravity affects it. In 2041, it should sail past us at a similar distance to last night's event. It should...

But don't worry too much about it. Apophis will be along in 2029. That should miss us too...

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