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The Dawn of Protoplanets

November 6, 2013

Did you know that NASA currently has a spacecraft zooming around the asteroid belt? I’m ashamed to admit that not only had I never heard of this mission, I also never considered the asteroid belt a cool or interesting place. Anyway, the spacecraft is named Dawn – not after a person, but because the goal of its mission is to study the “dawn” of our solar system.

Firstly, I wanted to know how the asteroid belt could tell us anything – much less give us information about the birth of our celestial ‘hood. Turns out there’s loads of info there! In the beginning, our solar system was nothing more than a bunch of gas and dust. Over huge amounts of time gravity began to pull chunks of matter together, getting larger and larger. Eventually the sun formed and began to heat things up, causing the leftover gas to blow away. At this point the planets were more or less formed, with the inner terrestrial planets being rocky (Mercury, Venus, Earth, Mars), and the outer planets being gas giants (Jupiter, Saturn, Uranus – hehe – and Neptune). But not Pluto because that guy SUCKS.

Seriously, Pluto, gtfo.

… jk I heart Pluto for life 🙂

Now, the asteroid belt lies between Mars and Jupiter, and it’s essentially full of all the leftover rocky bits that didn’t make it to full planet formation. They range in size from microscopic to dwarf planet (the largest, Ceres, has a diameter of 600 miles, roughly the size of Montana). As Jupiter grew, the massive tug of gravity from this planet was constantly stirring up the objects in this region, preventing them from ever forming into true planets.

What makes the asteroid belt interesting to scientists is that it divides the rocky planets from the icy giants of the outer solar system. So by studying objects in this region we can gain understanding of how each type of planet formed and why there seems to be an invisible divider between rocky and gassy.

Crunchy on the inside, soft on the outside

So… that’s the super simplified reasoning behind the Dawn mission. What’s particularly cool is that Dawn is visiting not one, but TWO objects. The first is an asteroid named Vesta, the second most massive object in the asteroid belt with a diameter of 320 miles. This is a dry, rocky object that will give us information about how the inner planets formed. Dawn completed it’s study of Vesta in 2011-2012, and you can read all the fun science things here.

Composite image of Vesta – they honestly refer to those craters as “snowman” (NASA)

Now it’s currently en route to the dwarf planet Ceres I mentioned earlier. In contrast to Vesta, Ceres has icy poles and potentially liquid water below it’s surface. This looks remarkably similar to many icy moons orbiting gas giants. Data from Ceres will hopefully give us information about the way objects formed in the outer solar system so that we can contrast it with the inner solar system.

What I like about this spacecraft is that it’s utilizing a fancy propulsion system to navigate from place to place. (For the record, the asteroid belt isn’t completely chock-full of boulders like Star Wars would have you believe… each object has literally hundreds to thousands of MILES around it.) Dawn is actually inside the asteroid belt anyway, cruising along at roughly the same speed as all the other rocky objects sort of like an inner tube on a lazy river ride. The main reason it requires propulsion is to change direction, allowing it to not only place itself into orbit around it’s targets, but also to steer its way to Ceres. The name of this technology is the super futuristic sounding “ion thruster.”

thruster, heh heh heh

Ion thrusting uses beams of chemically charged atoms, called ions, to propel the spacecraft. Unlike chemical propellents (ie – rockets), this type of system is completely unable to generate massive thrust all at once. However, by firing their ion beams for a way longer period they are able to bring the spacecraft to higher velocities in the long run using a smaller amount of propellant. Pretty cool. Also just pretty.

Upper Left: Xenon Hall Thruster (Xenon is used on Dawn) Upper Right: Bismuth Hall Thruster, Lower Left: Magnesium Hall Thruster, Lower Right: Zinc Hall Thruster.

For a mission with a relatively miniscule budget, I’m pretty darn impressed with Dawn. The two-for-one deal will provide a huge range of data to compare and will give insights to how our solar system started. So there is your five minute intro to protoplanets, the Dawn mission, and ion thrust technology!


From → SPACE

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