On approach to Ceres, the largest object in the asteroid belt

Dawn's closest view yet of the dwarf planet Ceres. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA's Dawn mission has been fairly low profile over the years since it launched in 2007, but it has already been a milestone for human space exploration, and it will set a few more milestones in the coming months.

First off, Dawn gets around using ion engines (remember the TIE fighters in Star Wars?), and is NASA's first exploration mission to use this mode of propulsion. Emitting a steady stream of energized xenon atoms, which propel the spacecraft forward based on Newton's Third Law (for every action, there is an equal and opposite reaction). This starts off very slow, but as the saying goes, slow and steady wins the race, as Dawn can keep its engines going continuously (something you can't do with a chemical rocket), and this constant thrust can get the spacecraft up to impressive speeds. Furthermore, the slow rate of the ion engines allows the spacecraft to not only smoothly pull into orbit around an object, simply letting the object's gravity capture it, but it can also leave orbit just as smoothly, which leads to Dawn's next feat.

Milestone number two was when the spacecraft gave us an extremely close-up view of the asteroid Vesta, as it orbited there for over a year, but since then it moved on, and is now on approach to the largest object in the asteroid belt, the dwarf planet 1 Ceres (shown to the right).

This series of images was snapped when Dawn was just 383,000 kilometers from Ceres - closer than the Moon is to the Earth. Although the details aren't crisp yet (these are zoomed-in, processed views from the originals, like this one), there are definitely surface features that can be picked out - especially the persistent 'bright spot' in the northern hemisphere, which the Hubble Telescope spied for the first time a little over a decade ago.

Hubble has still given us the best views of Ceres to date, even including these latest ones, but as of today, the 21st of January, we're exactly two weeks away from Dawn topping it. At that point, the spacecraft will have closed the distance to Ceres to just 290,000 km, and as JPL's Dawn Journal reports, "the pictures will be marginally better than the sharpest views ever captured by the Hubble Space Telescope."

That's milestone three, and we'll have numbers four and five over the next two months, as Dawn becomes the first spacecraft to orbit a dwarf planet come early March, and, at the same time, it becomes the first spacecraft to have orbited two different objects in the solar system.

NEXT PAGE: A brief, but long-overdue visit to distant Pluto