Not alone......

When people think of the asteroids*, they probably think of a nice, doughnut shaped, belt of a few thousand rocks going around the Sun in ...well, a nice, well behaved, doughnut shape.

It's not like that. It's a snowstorm, with snowflakes up to nine hundred kilometres wide. 

So, ladies and gentlemen, I present to you a youtube 'map': The asteroids of the inner solar system, in the order they were discovered, from 1980 to the present day. New discoveries in white, main belt asteroids in green, non-threatening Earth approachers in orange, potentially hazardous Earth crossers in red.

Stick with it until the end - put the video to full screen, in a dark room, for maximum effect. Then look up at the sky, and remember how damn crowded it is.....



Video above: A map of the inner solar system, showing the discovery of asteroids from 1980 to the present day. That's a lot of rocks. What really strikes me, though, is that by the end of the animation all the terrestrial planets are embedded in a swirling disk of flying rocks! It's worth remembering:  These blips are the remnants of the Suns protoplanetary disk  that gave birth to all the planets... Video courtesy of Scott Manley

As the automated sky surveys come on-line in the mid 1990s the count rate rockets, and around 2010 you can see the pattern of finds changes to one more parallel with direction of motion of Earth - that's the WISE space observatory coming on-line. And yes, I've posted this before, but this is the high definition, updated version...

Image above: Protoplanetary disks around star HD 141569A. Yes, it looks light pretty swirls of light, but what you're standing on right now came out of something a lot like that - and the asteroids are the leftovers. Image courtesy of Hubblesite.org [4].

Most of those rocks are less than half a kilometre across - which is plenty big enough to ruin your country, and there are lot of bigger ones. But although we do need to be aware of the potential hazard, those fragments of shattered protoplanets are an incredible scientific, and potentially material, resource.

And, from time to time, they treat us to spectacular displays of small fireworks.....


Video above: The Leonid meteor shower - the Leonids are a stream of dust and debris left behind by comet Tempel-Tuttle, so what you're seeing here are pieces of comet raining out of the sky. That's fine, and beautiful. Whole comets raining out of the sky would be more of a problem... Video courtesy of Space.com.

......Big fireworks.....


Video above: A huge meteorite explodes over south Africa, and gets caught on CCTV. The explosive force of such an 'air-burst' is usually comparable to a small nuke, but the meteorite goes bye-bye so far above the ground the damage is nil. Footage uploaded to youtube by knightskross

.......And leave us clues to what things are like beyond our blue skies.....

Image above: A cut and polished nickel-iron meteorite, showing the strange Thomson structure that occurs when the metal has cooled very, very, slowy, under microgravity - which means in the dying core of a protoplanet. Bits of the iron cores of protoplanets just fall out of the sky! But it's too rare to justify always wearing a hard hat. And a hard hat wouldn't be much good against most of these things anyway. 
But if you just like hard hats, feel free.......Image courtesy of The National Museum of Wales.

.... as well as likely delivering water , and the organic chemistry life is based on, to Earth.

So, if anyone ever tells you space is empty, do them a favour: Point them in the direction of the top video, and ask them how that qualifies as 'empty'...

* I  realise that most people don't think about asteroids on a daily basis. Look at that video - that's enough to get me thinking....