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Dwarf planet Ceres coming into view for Dawn spacecraft

Elizabeth Howell, News Writer
Dec 6, 2014, 16:41 UTC

Sen—It is only nine pixels wide, but a new image of dwarf planet Ceres is already making scientists salivate at the prospect of a closer look next year.

The 950-kilometre object was captured on 1 December by the Dawn spacecraft, which is speeding towards Ceres for a rendezvous in the spring, starting with a high-altitude orbit before spiralling down for a closer look.

"Now, finally, we have a spacecraft on the verge of unveiling this mysterious, alien world. Soon it will reveal myriad secrets Ceres has held since the dawn of the Solar System," stated mission director Marc Rayman, of NASA's Jet Propulsion Laboratory.


A magnified image of the view of the dwarf planet Ceres obtained by the Dawn spacecraft on 1 December, 2014. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Dawn's picture of Ceres was intended not only to be a glimpse of the dwarf planet, but also a calibration image for the science camera to get it ready for the close encounter. Ceres appears about as bright to the spacecraft as Venus does from Earth. The image was taken from 740,000 miles (1.2 million kilometers) away.

So little is known about Ceres that there is even a dispute about how to define it. Astronomers variously refer to the world as a protoplanet, a dwarf planet or an asteroid.

It's part of a larger debate about how to characterize some of the smaller objects in our solar system, which is coming to the forefront again as the New Horizons spacecraft speeds towards Pluto—the object famously demoted from planethood—which it will reach in 2015.


A close-up of Vesta's south pole region taken by the Dawn spacecraft. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Regardless of their definition, Ceres and Vesta—the other target of the Dawn mission—are the two largest objects in the asteroid belt. Dawn headed toward Vesta first after its launch in 2007, spending 14 months in orbit. Among its findings: that Vesta could have been affected by liquid water, that asteroids likely created dark splotches on Vesta's surface, and that it is not a round object.

The distance between Ceres and Vesta is greater than the distance between Earth and the Sun, NASA pointed out, but Dawn is closing the gap fast and expected to yield more insights about our solar system's history when it arrives there next year.

When Dawn enters its low altitude, the spacecraft will use a "hybrid" mode to keep pointed consistently, using a combination of thrusters and reaction wheels. This mode will be to conserve fuel and also to compensate for the disability of two (out of four) reaction wheels that cropped up as Dawn left Vesta in 2012. These pointing devices tend to be an issue in aging spacecraft. The hybrid mode is expected to work fine based on previous tests en route that NASA performed.


Dawn's route through the Solar System to get to Ceres. Image credit: NASA/JPL-Caltech