NASA's Dawn spacecraft has departed the giant asteroid Vesta, setting sail for a two-and-a-half-year journey to the dwarf planet Ceres.
Launched on Sept. 27, 2007, Dawn first entered orbit around Vesta on July 15, 2011 PDT (July 16 EDT). Over the past year, Dawn has comprehensively mapped the previously uncharted asteroid, revealing an exotic and diverse planetary building block.
For example, scientists learned that Vesta completely melted in the past, essentially forming a layered body with an iron core. The spacecraft also detected scarring from titanic collisions Vesta suffered in its southern hemisphere, surviving not one, but two colossal impacts in the last two billion years.
"Without Dawn, [we] would not have known about the dramatic troughs sculpted around Vesta, which are ripples from the two south polar impacts. [Remember], we went to Vesta to fill in the blanks of our knowledge about the early history of our solar system," explained Christopher Russell, Dawn's principal investigator, based at the University of California Los Angeles (UCLA).
"Dawn has filled in those pages, and more, revealing to us how special Vesta is as a survivor from the earliest days of the solar system. We can now say with certainty that Vesta resembles a small planet more closely than a typical asteroid."
Indeed, according to Dawn project manager Robert Mase, the spacecraft’s detailed observations are already helping scientists unlock some of the secrets of how the solar system, including our own Earth, was formed.
"As we respectfully say goodbye to Vesta and reflect on the amazing discoveries over the past year, we eagerly look forward to the next phase of our adventure at Ceres, where even more exciting discoveries await,” said Mase.
Dawn is slated to arrive at Ceres - the only dwarf planet in the inner Solar System and the largest asteroid - in approximately two-and-a-half-years.
As big across as Texas, Ceres' nearly spherical body has a differentiated interior - meaning that, like Earth, it has denser material at the core and lighter minerals near the surface.
Astronomers believe that water ice may be buried under Ceres' crust - as its density is less than that of the Earth's crust, and because the dust-covered surface bears spectral evidence of water-bearing minerals.
Ceres could even boast frost-covered polar caps. Astronomers estimate that if Ceres were composed of 25 percent water, it may have more water than all the fresh water on Earth. Of course, Ceres' water, unlike Earth’s, is expected to be in the form of water ice located in its mantle.