Prof. Disbrow sheds light on the exploration of Ceres, the dwarf planet
Launched way back in September of 2007, the NASA probe “Dawn” has been using its super-awesome ion engine to explore the asteroid belt since 2011. And, earlier this month, it did something that no other spacecraft has ever done: It entered orbit around a second extraterrestrial object, the dwarf planet Ceres.
What’s that? You’ve never heard of Dawn? Well, OK. I’ll back up a bit and fill in some of the blanks for folks that aren’t obsessed with this space stuff like I am.
As I said earlier, Dawn is on a mission to explore the asteroid belt. The asteroid belt is a ring of debris that exists in our solar system between the orbits of Mars and Jupiter. Basically, it’s a bunch of material that should have coalesced into a planet, but didn’t. Why? Well, we really don’t know. It could be that a planet did form and was destroyed by some other object, or it could be that Jupiter and Mars have been keeping the bits from coming together by the effects of their combined gravity.
I also mentioned that Dawn is using an “ion engine” to make its way around. This engine is based on the ion engine that was tested on the “Deep Space 1” mission back in the 1990s, and works in prettty much the same way: It throws ions out of the back of the probe to move the probe forward. Ions, in case you don’t remember, are just atoms with a charge (positive or negative) on them.
Now, if “throwing atoms out the back” of something sounds like it won’t produce much thrust, you’re right, it doesn’t. Dawn’s engines actually produce the same amount of force that’s needed to keep a piece of paper from falling to the ground. But when you apply that same tiny amount of force consistently over a long period of time, it can really take you places! Plus, it’s efficient.
When Dawn launched back in 2007, it was carrying 425 kg of xenon gas to use as fuel for its ion engines. Since then, that relatively tiny amount of fuel has driven the Dawn probe over 3 billion miles—and it still has some left.
As an added bonus, the ion engines also allow Dawn to perform maneuvers that older engines simply can’t do...like entering orbit around one body, and then leaving to go and orbit another. And that’s exactly what Dawn has done.
Back in July of 2011, Dawn began orbiting the asteroid Vesta. Discovered in 1807 and approximately 525 km wide, Vesta is one of the three largest objects in the asteroid belt. Dawn found Vesta to be an irregularly shaped body, with lots of impact craters and even some equatorial troughs that appear to have be caused by collisions with other bodies. (There is actually a class of meteorite, Eucrites, which is thought to have been ejected from Vesta before it found its way to Earth.)
Even though Vesta is large, it’s considered a “protoplanet,” not a dwarf planet. The reason? Dwarf planets, like Pluto, are spherical. Vesta, probably due to the sheer number and violence of the impacts it’s undergone, is lumpy and a bit oblong, which keeps it from gaining the “dwarf” designation.
Ceres, on the other hand, is a dwarf planet, and on September 5, 2012, Dawn left Vesta to begin its journey there. Earlier this month, Dawn arrived at Ceres and began sending back some spectacular photos. At 950 km in diameter, Ceres is the largest object in the asteroid belt, and, when it was first discovered in 1801, it was considered to be a full-fledged planet. (For comparison, Pluto, which was famously demoted from “planet” to “dwarf planet” a few years back, is 2,352 km in diameter.)
At this point, Dawn has just begun its exploration of Ceres, but it’s already revealed at least one very interesting feature. Previous observations of Ceres had shown a mysterious “bright patch” on its surface. As Dawn drew closer and closer, this patch resolved into not one, but two extremely bright points of light.
What are they? At this point, the best guess is that they are simply very reflective patches of ice, though some have suggested that there may be an active ice-volcano on Ceres!
Whatever they turn out to be, it’s clear that Dawn’s time at Ceres is going to be full of exciting discoveries. All of which you can read about on NASA’s official Dawn mission web site: http://dawn.jpl.nasa.gov
Steven Disbrow is a computer programmer who specializes in e-commerce and mobile systems development. He’s also an entrepreneur, comic-book nerd, writer, improviser, actor, sometime television personality and parent of two human children.