Dawn approaches Ceres

NASA’s latest mission will be our first close-up look at the dwarf planet


Dawn uses an ion propulsion system, allowing it to travel large distances on little fuel.

Credit: NASA/JPL-Caltech

The spacecraft Dawn is closing in on the dwarf planet Ceres. This is the first time that the object has been visited by a spacecraft, but is the second body that Dawn has visited in its mission.

Ceres is the largest object in the asteroid belt, measuring 950km in diameter. The probe is currently 640,000km away from the rocky body, and will enter into orbit in March this year.

Launched in 2007, the mission is one of NASA’s most ambitious plans in recent years, being the first mission to orbit around two different bodies beyond the Earth. The probe arrived at the protoplanet Vesta, the second largest body in the asteroid belt, in July 2011 before departing in September 2012. Ceres, however, is expected to be a very different world.

“Ceres is almost a complete mystery to us,” said Christopher Russell, principal investigator for the Dawn mission. “Ceres, unlike Vesta, has no meteorites linked to it to help reveal its secrets. All we can predict with confidence is that we will be surprised.”

The differences between the two worlds result from the times that they formed. Vesta formed earlier than Ceres, meaning it contained much more radioactive material. This increased the temperature of the body to the point where it retained only a small amount of its water.

Ceres meanwhile was cool enough that it maintained a thick ice mantle and may even have a liquid ocean under its crust. Dawn will take many images of the surface and analyse its composition, hoping to uncover how the world formed which will aid in understanding how other bodies in the Solar System came into being, including the planets.

This advanced mission has been made possible by using an ion propulsion engine, where an electrically charged grid is used to accelerate xenon gas and propel the spacecraft forward. The method takes several years to build up speed, but means that vast distances can be travelled using only a fraction of the fuel used by conventional methods.

“Orbiting both Vesta and Ceres would be truly impossible with conventional propulsion. Thanks to ion propulsion, we're about to make history as the first spaceship ever to orbit two unexplored alien worlds,” said Marc Rayman, Dawn's chief engineer and mission director.


For more information about Dawn's mission at Ceres be sure to pick up the February issue of BBC Sky at Night Magazine on sale 22 January 2014.


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