Pluto wasn’t the only dwarf planet to host a guest
this year. In March, four months before New Horizons
made it to Pluto, NASA’s Dawn probe entered Ceres’
orbit, becoming the first to see a dwarf planet up close.
Dawn launched in 2007 and visited asteroid Vesta first,
keeping that rock company for 14 months before flitting off to
its final destination: Ceres, the largest body in the asteroid belt
between Mars and Jupiter. Hovering around Ceres like a nosy
paparazzo, Dawn has been snapping photos and maneuvering
ever closer since March. It was expected to reach its closest and
permanent orbit, 230 miles above the surface, in December.
Ceres is so big, nearly 600 miles across, that astronomers
considered it a regular planet for almost 50 years after its
1801 discovery. That size means gravity has pulled Ceres into
a sphere, with a core of rock, an icy coating and perhaps an
ocean of liquid water locked between. But Ceres remained
fuzzy from afar, until Dawn revealed a fascinating world with
miles-high mountains and miles-deep craters. Ceres’ surface
is covered by landslides and plump with ice. The diminutive
planet is more dynamic than scientists expected.