The Dawn Mission: Investigating the Mystery of Ceres and Vesta
NASA’s Dawn spacecraft has been in orbit around the asteroid Vesta (above image) for some months now. This is a cool space exploration mission from a number of perspectives. It’s the first spacecraft that is going to orbit two targets, after it finishes its mission around Vesta it’s moving on the asteroid Ceres, recently promoted to the dwarf planet Ceres. Dawn is performing this trick by using a new and innovative propulsion system, an ion drive, as opposed to rockets. Basically it’s an electric thruster that fires a stream of ions at a very high speed, thus giving a large amount of thrust for a small amount of fuel. It doesn’t give very much thrust, but it adds up. Previous multi-target missions were limited to flybys, so ion drives are the wave of the future for exploring multiple targets.
So why Ceres and Vesta, and what is the mystery? Basically it is believed that Ceres and Vesta are the last two remnant protoplanets from the creation of the Solar System, literally leftover building blocks, from over 4.5 billion years ago. By protoplanet, I mean a lump of stuff that got so big that the insides started to melt from radioactive decay so they formed a core, mantle and crust like the solid planets like Earth and Mars. (There were other surviving protoplanets, because we have chunks of them that fell on Earth as meteorites, but they were all shattered by collisions in the billions of years since their creation.) And as such protoplanets, study of Ceres and Vesta should give clues about the origin of the planets, including Earth. Granted, this is pretty much pure academic research at this point, but simply exploring the Solar system and seeing what’s out there is a a pretty good reason in and of itself. There have been endless surprises up to now, and no reason to expect anything less.
The reason that both Ceres and Vesta are being investigated is because while they both originated at about the same time, they are apparently very different. Vesta is basically a lump of iron encased in a shell of olivine, a mineral. It’s a few hundred miles across, with the approximate surface area of Ontario, or Texas and Oregon, or two Spains. Surface temperatures range from -190c to a balmy -20c. It has no atmosphere and very little, if any, water. Ceres on the other hand has a rocky/iron core like Vesta, but then an icy mantle and all sorts of water ice, carbonates, and clays. And Ceres might even have a vast liquid water ocean under a layer of ice. Ceres is bigger than Vesta, being the smallest known dwarf planet. It has about the same surface area as Argentina, and might even be a bit warmer than Vesta. It even possibly has a tenuous atmosphere.
So why would one protoplanet be dry as a bone, and the other have water as a major component? No one knows, that’s easily the biggest question the Dawn Mission set out to answer. Perhaps they formed in different regions of the Solar System where conditions were different. Or perhaps something happened to the water that was on Vesta. Something most definitely happened to Vesta. See the scalloped edge at the upper right on the above image? That’s the edge of a mysterious crater, Rheasilvia, that is about 460 kilometres (290 mi) wide, centred at the south pole. That’s about 80% the diameter of Vesta, it happened about a billion years ago, and it blasted a small but measurable percentage of Vesta into space. Rheasilvia is one of the largest craters in the Solar System, and a whole family of asteroids was created by it. It also likely created grooves around the equator, visible at the upper left. And likely there will be evidence of the impact on the north pole of Vesta as well, opposite Rheasilvia crater, but that won’t be imaged until later this year.
And then on to Ceres, arriving in 2015. Now that’s going to be too cool for words. Ceres has been proposed as a potential human colony site, and might even harbour life. Heck, some have even suggested Earth’s life originated on Ceres. See, two more future blogs, it’s hopeless.
Creation Science Legal Notice: In voluntary compliance with recently passed and proposed laws in a number of US states, I am required to state that the age and origins of the Solar System, Ceres, and Vesta, are all theoretical only. An alternate theory is that the entire Solar System, indeed, the entire Universe, was created some 6,000 years ago by a supernatural entity known as God over a period of six days, and that the vast body of overwhelming factual scientific evidence that contradicts this theory was created by Satan, another supernatural entity, after the fact to conceal God’s handiwork and confuse humanity.
(The above image of Vesta was taken by the Dawn spacecraft, and thus by NASA, and is basically OK to use for non-commercial purposes. Credit and copyright, NASA. And to my non American reader, it’s not a joke, Evangelists in the USA are tirelessly trying to get their religious creation myths taught in public schools as if they were scientific theories on par with the Big Bang and Evolution. If it’s happening in your country too, I feel your pain. I think they plan on bringing back slavery next.)