Today’s factismal: For the first time in human history, we have launched a spacecraft that has orbited two bodies other than the Earth!
Today marks a very special day in spaceflight history. That’s because, as of today, spaceflight no longer means orbiting just one new planet. Up until today, every probe that we sent out would orbit just one planet (other than the Earth). If the probe was sent to the Moon, it could orbit the Moon but it couldn’t orbit the Moon and then head over to Mars. If it was sent to Mars, it could orbit Mars but it couldn’t orbit Mars and then head over to Jupiter. And so on. If we wanted to send a probe to more than one planet (as we did with the Voyager probes) then we had to send it on fly-by trajectories that let us get close to each planet but not spend much time there. Naturally, that limited both the quantity and the quality of the science that could be done and the pictures that could be taken. (How many pictures could you take of Disneyworld if you were driving past at 600 mph?) But as of today, that is no longer true. Today the DAWN probe has gone into orbit around Ceres after previously orbiting Vesta.
DAWN was able to do this thanks to her ion engine. This rocket motor is so weak that it couldn’t lift the probe a millimeter off the ground on Earth. But in space, even a weak thrust adds up over time, which allowed DAWN to slowly move away from Earth and into the asteroid belt where Vesta and Ceres live. These two rocks are the largest of the asteroids and the smallest of the planets (if you use the planetological community’s definition). They formed early on as the other planets were gobbling up all of the rocks and dust that they could in order to become big and gravitationally strong. As a result, learning about these two baby planets can tell us a lot about how bigger planets form. Even better, it is possible that Ceres has a thick layer of water which may still be partially liquid; as a result, Ceres is one of the places in the Solar System that may harbor life as we know it.
But the best thing about Ceres is what we don’t know about what we do know about it. For example, we know that Ceres has several spots that appear very bright when the spacecraft is in just the right place. But what we don’t know about those spots is why they are so bright. Is it due to a frozen lake of water ice at the bottom of a crater? Is it the plume of a cryovolcano? Is it the gleam of metal? Right now, we don’t have enough information to know for sure (my money is on the water ice). DAWN is going to change all of that.
DAWN will take pictures of the entire surface of Ceres. And here’s the cool part – you will get to see those pictures just as soon as the scientists do. And here is the even cooler part – you can do science with those pictures yourself! The DAWN mission team and NASA have asked citizen scientists like you to look through the pictures as they arrive and identify any interesting landforms such as impact craters, volcanoes, and lava flows. You’ll even have the opportunity to name some of the features. If you’d like to take part (or just look through the amazing images), then fly over to: