I can remember for the longest time being completely unaware of the asteroid belt between Mars and Jupiter. After learning about it however I never paid much more thought to it, although I was curious about how there seemed to be a line that separated the smaller, rocky planets from the large gas giants of our solar system (negating Pluto, of course). As my interest in space grew I began to wonder how any spacecraft that had ventured past Mars (there have been 9 of them) hadn’t managed to have a run in with a stray asteroid. As it turns out there’s a few reasons for that, and I find them quite fascinating.
The first is that the average density of the asteroid belt is extremely low with the total mass contained within the entire system being less than 4% of that of our Moon. Our best calculations then put the odds of a satellite coming into (unintended) contact with an asteroid in this region at about a billion to one, or so unlikely that you wouldn’t even consider it a risk. The images of the asteroid belt that many are familiar with make it look far more densely packed than it really is, much like this series of pictures that shows all the artificial satellites of Earth. That’s not to say the amount of junk we’ve sent up around ourselves isn’t an issue, but an accurate scale representation of each satellite wouldn’t look anywhere near as packed as they do.
What fascinates me the most about the asteroid belt however is how the majority of the mass is concentrated within 4 objects, with the two largest of these being 4 Vesta and an object big enough to be classed as a dwarf planet called Ceres. In astronomical terms they’re right in our backyard but even with our most powerful space based telescope we’re still only able to capture relatively blurry representations of them, shrouding these little heavenly bodies in mystery. Ceres especially so, with a series of images showing a massive bright spot moving across its surface of which its nature is still unknown.
So fascinating are these objects that NASA launched a mission to both of them, named Dawn, back in 2007. This particular spacecraft is something of a novelty in of itself as well as it is the first purely exploratory mission to use only ion thrusters for propulsion. It needs these highly efficient engines as it will be the first spacecraft to launch to its target, orbit it for a set amount of time and then set off again to approach yet another target. To do this it is carrying with it over 400kg of propellant enough for it to change its velocity by over 10km/s, a figure well above that of any other spacecraft that has come before it. It may take its time in doing so, but it’s still an incredible achievement none the less.
Dawn is scheduled to arrive at its first target, 4 Vesta, in just over a month and it has already begun sending back pictures and video of this strange mega-asteroid. They’re not much to look at right now but once its closer the imagery will become much clearer, revealing the nature of all the blurry spots we’ve as of yet only been able to speculate about. Dawn will spend a year surveying 4 Vesta before it sets off on its long journey for Ceres, for which it is not expected to reach until February 2015. Its a long wait to get a better look at something that’s so small compared to nearly everything in our solar system, but the prospect still excites me immensely.
Perhaps its the combination of their close proximity yet relative lack of information about these two little bodies that makes them so interesting, they’re just sitting there begging to be investigated. The next year will reveal all sorts of insights into the asteroid belt and its second largest contributer which will in turn tell us something about Ceres itself. We’re still a long, long way away from seeing Ceres in the flesh (or rock, as it were) but any information that Dawn sends back is valuable and I can’t wait to see what it brings us.