In the coming months we will discuss other intriguing activities and how Dawn will make measurements never even considered before. But for now, let's look at how this extension came about.

As readers of the Dawn Journals know (and as you will be reminded below), there has been very good reason in recent years to believe the spacecraft would not operate beyond the end of its prime mission. However, the veteran explorer is in very good health. It is one of Earth's most experienced and capable ambassadors to the cosmos, we want to squeeze as much out of this mission as we can. Ever resourceful, the Dawn team recognized in March 2016 that the probe had the capability to do yet more and decided to give NASA Headquarters a unique choice: remain at Ceres (as always expected) or go elsewhere.

It is worth pondering how extraordinary this is. Most spacecraft can only make minor adjustments to their trajectories, so at the end of their prime missions, they generally go wherever they were already headed. If a spacecraft is in orbit around some planetary body, it remains in orbit. If a spacecraft is not in orbit, having previously flown past one or more bodies that orbit the sun, its course is largely determined by the targeting for the last encounter. A planet's gravity may have redirected it, but otherwise its propulsion system has to do the work, and that usually can produce only a tiny change in direction. If a spacecraft is not already in orbit around a planetary body, it won't be able to enter orbit.

Dawn is different. With its uniquely capable ion propulsion system, Dawn is the only spacecraft ever to travel to a distant destination, orbit it, later break out of orbit, then travel to another faraway destination, and orbit it. And even while in orbit around Vesta and Ceres, Dawn maneuvered extensively, optimizing its orbits for its scientific investigations. And yet this remarkable ship can do still more. It has the capability to leave its second destination and continue its travels.

Dawn's brilliant and creative navigators analyzed possible missions to more than 68,000 known objects. That alone is a nice illustration of the powerful potential.

The project team very quickly narrowed the list to the most interesting body Dawn could reach after leaving Ceres, a large asteroid named Adeona. That mission offered the best alternative to further studies of the dwarf planet.