Sen—At around 1239 UTC (4:39 a.m. PST) on Friday Mar. 6, NASA's Dawn spacecraft became the first mission to achieve orbit around a dwarf planet.

The spacecraft was approximately 61,000 km (38,000 miles) from Ceres when it was captured by the dwarf planet's gravity. At 1336 UTC (5:36 a.m. PST) mission controllers at NASA's Jet Propulsion Laboratory (JPL) in California received a signal that Dawn was healthy and thrusting with its ion engine, indicating that the spacecraft had entered orbit as planned.

Ceres now has its own satellite! Dawn is currently in orbit around Ceres at 16 per cent of the average distance between Earth and the Moon. It is also 498 million km (310 million miles) from Earth. Radio signals, traveling at the speed of light, take 55 minutes to make the round trip.

Dawn launched from Earth in September 2007, its goal is to investigate in detail two of the most massive bodies in the main asteroid belt, baby protoplanets whose growth was interrupted by the formation of Jupiter and its disruptive gravitational pull.

The mission now has the double distinction of being the first spacecraft to orbit two extraterrestrial targets, having explored the giant asteroid Vesta between 2011 and 2012. Coincidentally Dawn’s arrival at Vesta was exactly one Vestan year ago earlier this week. After 14 months of intensive operations at Vesta, Dawn resumed its interplanetary voyage toward Ceres.

Discovered in 1801, Ceres was first designated as a planet. It was later redesignated as an asteroid, and then in 2006 was classified as a dwarf planet along with Pluto, Haumea, Makemake and Eris. Ceres is the largest object between the Sun and Pluto that had not previously been visited by a spacecraft.

"Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet," said Marc Rayman, Dawn chief engineer and mission director at JPL. "Now, after a journey of 3.1 billion miles (4.9 billion km) and 7.5 years, Dawn calls Ceres 'home'."

The spacecraft's trajectory means it is currently on the side of Ceres that faces away from the Sun, so the most recent images taken by Dawn on Mar. 1 show Ceres as a crescent. As Dawn emerges from Ceres' dark side around mid April, it will deliver ever-sharper images and a myriad of other measurements as it spirals closer and closer to Ceres during the year.

"We feel exhilarated," said Chris Russell, principal investigator of the Dawn mission at the University of California, Los Angeles (UCLA). "We have much to do over the next year and a half, but we are now on station with ample reserves, and a robust plan to obtain our science objectives."

The three principal scientific drivers for the mission are first to capture the earliest moments in the origin of the Solar System to understand the conditions under which such objects formed. Second, to determine the nature of the building blocks for the terrestrial planets and finally, to contrast the formation and evolution of Vesta and Ceres that followed very different evolutionary paths.

Dawn will now remain in an orbit around Ceres for the rest of its operational life.

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