Tomorrow’s asteroid near-miss is only a hint of what’s really out there

As asteroid 2012 DA14 makes its close pass by us tomorrow, it gives us a sobering look at how Earth is locked in a cosmic shooting gallery, but in reality this 50-metre wide rock is only one hundreds of known asteroids that are flying around us, as shown in this latest map from the Armagh Observatory:

Daily map of asteroids within 0.3AU of the Earth

This 3D map shows the current location of asteroids in our vicinity. A dot represents the position of each asteroid, along with the asteroid's name. The vertical line for each entry joins the dot to the plane of Earth's orbit. If the dot is at the top of the line, that means the asteroid is above the plane of our orbit, and if the dot is at the bottom of the line, that means it's below the plane of our orbit. Arrows from the dot show the direction the asteroid is traveling today, and the color of each asteroid's map entry indicates its threat level.

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Green entries are not approaching the Earth currently and thus do not pose any threat. Yellow entries are asteroids that approach the Earth's orbit, but do not cross it. These are called Amor asteroids, after the first such asteroid to be found, and although they pose no threat to us now, there is the possibility of them being diverted by the gravitation influence of the planets and thus becoming a danger to us in the future. A red entry — thankfully absent from the map — would indicate an asteroid that is passing across Earth's orbit, which can become a significant threat at some point in the future (these are called Apollo asteroids).

The map certainly shows that there's a lot going on around us, but before you get too freaked out about it, I should point out the scale that the map is using. This is best illustrated by the red ring that surrounds the Earth at the centre of the image. That's not the orbit of our geosynchronous satellites. It's also not the orbit of the Moon. It's actually 10 times the distance that the Moon orbits the Earth.

In fact, the entire image above is showing the objects that are up to one-third of an 'astronomical unit' (AU) away from the Earth. An astronomical unit is the average distance between the Earth and the Sun, which is nearly 150 million kilometres, so the map is showing objects up to 50 million kilometres away from us. That is a lot of space!

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If you want to be really freaked out about how many asteroids are whizzing around above our heads and how close they come to the Earth, check out the big map on the Armagh Observatory page. I also recommend watching the accompanying movie, which shows 400 days of asteroid activity in the inner solar system (remember that we're the third blue dot out from the Sun).

(Image courtesy: Armagh Observatory, Armagh, Northern Ireland)

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