Dwarf planet welcomes first visitor

A NASA spacecraft flawlessly slipped into orbit around Ceres on Friday in the first visit to a dwarf planet after a nearly eight-year journey.

The Dawn craft will circle the dwarf planet for more than a year, exploring its surface and unravelling its mysteries.

“It went exactly the way we expected. Dawn gently, elegantly slid into Ceres’ gravitational embrace,” said mission chief engineer Marc Rayman at NASA’s Jet Propulsion Laboratory, which manages the $473-million mission.

Ceres is the second and final stop for Dawn, which launched in 2007 on a voyage to the main asteroid belt, a zone between Mars and Jupiter that’s littered with rocky leftovers from the formation of the sun and planets 4½ billion years ago.

Dawn will spend 16 months photographing the icy surface. It previously spent a year at Vesta exploring the asteroid and sending back stunning close-ups of its lumpy surface before cruising on to the Texassized Ceres, the largest object in the asteroid belt.

The 4.8-billion-kilometre trip was made possible by Dawn’s ion propulsion engines, which provide gentle yet constant acceleration and are more efficient than conventional thrusters.

As Dawn approached Ceres, it beamed back the best pictures ever taken of the dwarf planet. Some puzzling images revealed a pair of shiny patches inside a crater — signs of possible ice or salt. Scientists hope to get a better glimpse of the spots when the spacecraft spirals closer to the surface. It’ll also study whether previously spotted plumes of water vapour continue to vent.

Dawn is currently in Ceres’ shadows and won’t take new pictures until it emerges in April, Rayman said.

Discovered in 1801, Ceres — measuring 965 kilometres across — is named after the Roman goddess of agriculture and harvest. It was initially called a planet before it was demoted to an asteroid and later classified as a dwarf planet. Like planets, dwarf planets are spherical in shape, but they share the same celestial neighbourhood with other similar-sized bodies.

With its massive solar wings spread out, Dawn is about the size of a tractortrailer, measuring 20 metres from tip to tip.

Dawn carries an infrared spectrometer and a gamma ray and neutron detector to study the surface of Ceres from orbit. In the coming months, it will spiral down to within 378 kilometres of Ceres’ surface where it will remain long after the mission is over.