Legacy of NASA's Dawn, Near the End of its Mission
Now drawing to a close, the mission that explored the planet-like worlds of Vesta and Ceres revealed Solar System time capsules and broke engineering barriers.
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."NASA's Dawn spacecraft turned science fiction into science fact by using ion propulsion to explore the two largest bodies in the main asteroid belt, Vesta and Ceres. The mission will end this fall, when the spacecraft runs out of hydrazine, which keeps it oriented and in communication with Earth.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."Engineering FeatsDawn 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.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 PastAll 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."Spectacular CeresThere 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."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 VestaAt 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.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 reactionwheels failedearlier in the mission, leaving it heavily dependent on this key fuel.
When Dawnruns 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.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/missionMore information about Dawn is available at the following sites:https://www.nasa.gov/dawnhttps://dawn.jpl.nasa.gov