An artist’s concept of the Dawn spacecraft arriving at Ceres. Today, dwarf planet Ceres became the first such planet to have company over. The visitor is NASA’s Dawn spacecraft, which reached its final destination — an orbit around this 590-mile-wide ball of ice and rock — after more than seven years in space. And now that Dawn is finally all up on this space rock, astronomers can take sharp snapshots of its surface and learn about what makes Ceres Ceres, which they’ll do for the next 16 months. In the process, they will investigate why some planet-like objects didn’t quite grow into planets (sorry, Pluto — we're looking at you), what the solar system was like billions of years ago, and what that tells us about Earth today.