NASA’s Dawn mission is drawing to a close after 11 years of breaking new ground in planetary science, gathering breathtaking imagery, and performing unprecedented feats of spacecraft engineering.
Dawn’s mission was extended several times, outperforming scientists’ expectations in its exploration of two planet-like bodies, Ceres and Vesta, that make up 45 percent of the mass of the main asteroid belt. Now the spacecraft is about to run out of a key fuel, hydrazine. When that happens, most likely between mid-September and mid-October, Dawn will lose its ability to communicate with Earth. It will remain in a silent orbit around Ceres for decades.
“Although it will be sad to see Dawn’s departure from our mission family, we are intensely proud of its many accomplishments,” said Lori Glaze, acting director of the Planetary Science Division at NASA Headquarters in Washington. “Not only did this spacecraft unlock scientific secrets at these two small but significant worlds, it was also the first spacecraft to visit and orbit bodies at two extraterrestrial destinations during its mission. Dawn’s science and engineering achievements will echo throughout history.”
When Dawn launched from Cape Canaveral Air Force Station in Florida in September 2007, strapped on a Delta II-Heavy rocket, scientists and engineers had an idea of what Ceres and Vesta looked like. Thanks to ground- and space-based telescopes, including NASA’s Hubble Space Telescope, the bodies in the asteroid belt between Mars and Jupiter were visible — but even the best pictures were fuzzy.
From 2011 to 2012, Dawn swept over Vesta, capturing images that exceeded everyone’s imaginings— craters, canyons and even mountains. Then on Ceres in 2015, Dawn showed us a cryovolcano and mysterious bright spots, which scientists later found might be salt deposits produced by the exposure of briny liquid from Ceres’ interior. Through Dawn’s eyes, these bright spots were especially stunning, glowing like diamonds scattered across the dwarf planet’s surface.
“Dawn’s legacy is that it explored two of the last uncharted worlds in the inner Solar System,” said Marc Rayman of NASA’s Jet Propulsion Laboratory in Pasadena California, who serves as Dawn’s mission director and chief engineer. “Dawn has shown us alien worlds that for two centuries were just pinpoints of light amidst the stars. And it has produced these richly detailed, intimate portraits and revealed exotic, mysterious landscapes unlike anything we’ve ever seen.”
Dawn is the only spacecraft to orbit a body in the asteroid belt. And it is the only spacecraft to orbit two extraterrestrial destinations. These feats were possible thanks to ion propulsion, a tremendously efficient propulsion system familiar to science-fiction fans and space enthusiasts.
Pushed by ion propulsion, Dawn reached Vesta in 2011 and investigated it from surface to core during 14 months in orbit. In 2012, engineers maneuvered Dawn out of orbit and steered it though the asteroid belt for more than two years before inserting it into orbit around the dwarf planet Ceres, where it has been collecting data since 2015.
All the while, scientists gained new insight into the early stages of our Solar System, fulfilling Dawn’s objective. The mission was named for its purpose: to learn more about the dawn of the Solar System. It targeted Ceres and Vesta because they function as time capsules, intact survivors of the earliest part of our history.