Artist's rendering showing NASA's Dawn spacecraft maneuvering above Ceres. Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

I've been following the Dawn mission since its launch; my very first lecture as a Solar System Ambassador was to the Warren Astronomical Society about the Dawn mission at asteroid Vesta. Now, the spacecraft's hydrazine propellant is running out, and when it does, the spacecraft will be unable to communicate with Earth - ending the mission. I'm planning on a good cry for that day; I can only imagine how Marc Rayman and his mission team will feel.

The following is a JPL press release about the Dawn end of mission:

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.

Asteroid 4 Vesta. Image credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA

"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."

Engineering Feats

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. Dawn pushed the limits of the system's capabilities and stamina, showing how useful it is for other missions that aim to visit multiple destinations.

Next-Generation Plasma-Thrusters, similar to the one on the Dawn Spacecraft, being developed at Michigan Technological University. Credit: MTU

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.

Window into the Past

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. And the duo delivered, giving scientists insight into the original building blocks of the Solar System.

"Vesta and Ceres have each told their story of how and where they formed, and how they evolved -- a fiery magmatic history that led to rocky Vesta and a cooler, water-rich history that resulted in the ancient ocean world Ceres," said Carol Raymond of JPL, principal investigator of the Dawn mission. "These treasure troves of information will continue to help us understand other bodies in the Solar System far into the future."

Animation of  Ceres. Credit: NASA/JPL-Caltech

Spectacular Ceres

There was so much that scientists didn't know about Ceres before Dawn arrived. Raymond wondered whether they might find Ceres covered with a smooth, young surface -- an enormous cue ball with a frozen crust. Instead, they found the dwarf planet wearing the chemistry of its old ocean. "What we found was completely mind-blowing. Ceres' history is just splayed all over its surface," she said.

Some of the dazzling bright spots turned out to be brilliant salty deposits, composed mainly of sodium carbonate that made its way to the surface in a slushy brine from within or below the crust.

The findings reinforce the idea that dwarf planets, not just icy moons like Enceladus and Europa, could have hosted oceans during their history -- and potentially still do. Analyses from Dawn data suggest there may still be liquid under Ceres' surface and that some regions were geologically active relatively recently, feeding from a deep reservoir.

One of Dawn's biggest reveals on Ceres lay in the region of Ernutet Crater. Organic molecules were found in abundance. Organics are among the building blocks of life, though Dawn's data can't determine if Ceres' organics were formed by biological processes.

Enhanced color composite image, made with data from the framing camera aboard NASA's Dawn spacecraft, shows the area around Ernutet crater. The bright red portions appear redder with respect to the rest of Ceres. In a 2017 study in the journal Science, researchers from the Dawn science team found that these red areas around Ernutet are associated with evidence of organic material. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

"There is growing evidence that the organics in Ernutet came from Ceres' interior, in which case they could have existed for some time in the early interior ocean," said Julie Castillo-Rogez, Dawn's project scientist and deputy principal investigator at JPL.

Vibrant Vesta

At Vesta, Dawn's investigation into the early Solar System found a 4.5-billion-year-old witness it could interrogate. Dawn mapped the craters of the planet-like world and revealed that its northern hemisphere had experienced more large impacts than expected, suggesting there were more large objects in the asteroid belt early on than scientists thought.

Vesta held other surprises as well. While it's technically classified as an asteroid, that label belies the rich and varied terrain Dawn revealed, and the planet-like processes that Vesta experienced. Hubble had relayed images of a mountain at the center of an enormous basin now called Rheasilvia. Dawn's mapping showed it to be twice the height of Mt. Everest, and it revealed canyons that rival the Grand Canyon in size. Dawn also confirmed Vesta as the source of a very common family of meteorites.

This set of images from NASA's Dawn mission shows topography of the southern hemisphere of the giant asteroid Vesta and a map of Vesta's gravity variations that have been adjusted to account for Vesta's shape. The shaded relief map on the left shows the outlines of the two ancient basins, Rheasilvia and Veneneia. On the right is a map of the residual gravity field created by removing the gravity due to the hills and valleys within the crustal layer, revealing the signature of variations in density.

Red shows the strongest gravitational pull in this scheme, measured in milligal units, and dark blue shows the weakest. Milligals are a unit of acceleration due to gravity. The large central peak of the Rheasilvia basin, which appears as the yellow area just above and to the left of center, has a small positive residual gravity anomaly. This indicates the crust there is denser, coming from deeper within the body, or perhaps is less fractured. The gravity lows near the basin rim on the right, shown in dark blue, likely indicate rock that is lighter as a result of being pulverized by the two impacts.

The topography model is derived from framing camera images from Dawn's high-altitude mapping orbit (420 miles or 680 kilometers above the surface) and the gravity data come from the low-altitude mapping orbit (130 miles or 210 kilometers above the surface). Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Now, near the end of Dawn's second extended mission at Ceres, the spacecraft has continued to gather high-resolution images, gamma ray and neutron spectra, infrared spectra, and gravity data. Almost once a day, it will swoop over Ceres about 22 miles (35 kilometers) from its surface -- only about three times the altitude of a passenger jet -- gathering valuable data until it expends the last of the hydrazine that feeds thrusters controlling its orientation. Dawn's reaction wheels failed earlier in the mission, leaving it heavily dependent on this key fuel. When Dawn runs out in the next month or two, the spacecraft will lose its ability to communicate with Earth, but it must not crash into Ceres.

Because Ceres has conditions of interest to scientists who study chemistry that leads to the development of life, NASA follows strict planetary protection protocols for the disposal of the Dawn spacecraft. Unlike Cassini, which deliberately plunged into Saturn's atmosphere to protect the system from contamination -- Dawn will remain in orbit around Ceres, which has no atmosphere.

Dawn orbiting Ceres - Sept. 21, 2018. Credit: NASA Eyes on the Solar System / Bob Trembley.

Engineers designed Dawn's final orbit to ensure it will not crash for at least 20 years -- and likely decades longer.

Rayman, who led the team that flew Dawn throughout the mission and into its final orbit, likes to think of Dawn's end this way: as "an inert, celestial monument to human creativity and ingenuity."

More on Dawn's mission legacy here: https://dawn.jpl.nasa.gov/mission/toolkit/

The Dawn mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. JPL is responsible for overall Dawn mission science. Northrop Grumman in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team.

For a complete list of mission participants, visit: https://dawn.jpl.nasa.gov/mission

More information about Dawn is available at the following sites: https://www.nasa.gov/dawn and https://dawn.jpl.nasa.gov

News Media Contact

Gretchen McCartney
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-6215
gretchen.p.mccartney@jpl.nasa.gov

Dwayne Brown / JoAnna Wendel
NASA Headquarters, Washington
202-358-1726 / 202-358-1003
dwayne.c.brown@nasa.gov / joanna.r.wendel@nasa.gov

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Simulation of Dawn orbiting Ceres on June 24, 2015. Credit: NASA Eyes on the Solar System.