Dawn's legacy near the end of NASA's mission

NASA's Dawn mission is coming to an end after 11 years of global science experience, bringing together breathtaking images and unprecedented achievements in space engineering.

Dawn's mission has been extended several times by exploring Ceres and Vesta which, combined, account for 45% of the mass of the main asteroid belt. Now, the spacecraft is about to miss an essential fuel, hydrazine. When that happens, probably between September and October, Dawn will lose her ability to communicate with Earth. It will remain in silent orbit around Ceres for decades.

"While sad to see Dawn's departure from our missionary family, we are extremely proud of her many accomplishments," said Lori Glaze, Acting Director of the Planetary Science Division at Washington headquarters. "This spacecraft not only unlocked scientific secrets on these two small but significant worlds, but it was also the first spacecraft to visit and orbit bodies on two extraterrestrial destinations during its mission. Dawn's scientific and technical achievements will resonate throughout history. "

Dawn took off from Cape Canaveral Air Base in September 2007, attached to a Delta II-Heavy rocket. From 2011 to 2012, the spacecraft swept Vesta, capturing images of craters, canyons and even mountains of this planet-like world.

In 2015, Dawn's cameras spotted a cryovolcano and mysterious bright spots on Ceres, which scientists later discovered were salt deposits produced by brackish liquid exposure from inside Ceres.

"Dawn's legacy is that he has explored two of the last unexplored worlds of the internal solar system," said Marc Rayman of NASA's Jet Propulsion Laboratory in Pasadena, California, who is Dawn's chief of mission and chief engineer. . "Dawn showed us extraterrestrial worlds that for two centuries were just points of light among the stars. And he produced these richly detailed intimate portraits and revealed exotic and mysterious landscapes different from anything we've ever seen. "

Engineering practices

Dawn is the only spacecraft to orbit a body in the asteroid belt. And it's the only spacecraft to orbit two extraterrestrial destinations. These achievements were made possible by ionic propulsion, an extremely efficient propulsion system known to science fiction fans and space enthusiasts. Dawn has pushed the limits of the capabilities and endurance of the system, showing how useful it is for other missions to visit multiple destinations.

Driven by ionic propulsion, Dawn reached Vesta in 2011 and examined it from the surface to the heart for 14 months in orbit. In 2012, engineers maneuvered Dawn out of its orbit and piloted it into the asteroid belt for more than two years before inserting it into orbit around the dwarf planet Ceres, where it collection of data since 2015.

The mission was aimed at Ceres and Vesta as they function as time capsules, intact survivors of the first part of our history.

"Vesta and Ceres have each told how and where they were formed, and how they evolved – a fiery magmatic story that led to Vesta and a colder, water-rich story that culminated in the ancient oceanic world of Ceres. . Raymond de JPL, principal investigator of the Dawn mission. "These information treasures will continue to help us understand other bodies in the solar system in the future."

Ceres spectacular

On the surface of Ceres, scientists have discovered the chemistry of an ancient ocean. "What we found was completely mind-blowing. The story of Ceres is only on its surface, "said Raymond.

Some of the bright spots turned out to be bright, salty deposits, consisting mainly of sodium carbonate that made its way to the surface in a melting brine inside or below the crust.

The results reinforce the idea that dwarf planets, not just icy moons like Enceladus and Europa, could have hosted oceans in their history – and could still do so. The analyzes from Dawn's data suggest that there may still be some liquid on the surface of Ceres and that some areas were relatively recently geologically active, feeding in a deep reservoir.

One of Dawn's biggest revelations about Ceres was in the Ernutet crater area. Organic molecules have been found in abundance. Organic products are part of life, although Dawn's data do not determine whether organic matter from Ceres is derived from biological processes.

"There is growing evidence that Ernutet's organic material originated from within Ceres, in which case it may have existed for some time at the beginning of the Inner Ocean," says Dawn Project scientist Julie Castillo-Rogez. assistant researcher at JPL.

Vibrant Vesta

At Vesta, Dawn mapped the craters of this planet-like world and revealed that its northern hemisphere had suffered larger impacts than expected, suggesting that there were more large objects in the belt. asteroids that scientists thought.

In 1996, the Hubble Space Telescope retransmitted images of a mountain in the center of a huge Vesta basin now called Rheasilvia. Dawn's mapping showed that it was twice as high as Mt. Everest, and he revealed canyons that rival the size of the Grand Canyon.

Dawn also confirmed that Vesta was the source of a widespread family of meteorites.

Towards the end

Dawn continued to collect high-resolution images, gamma-ray spectra and neutron spectra, infrared spectra, and gravimetric data at Ceres. Almost once a day, it will fly over Ceres at about 35 kilometers from its surface, about three times the altitude of a jet plane, collecting valuable data until it spends the last hydrazine that powers the thrusters .

As Ceres presents interesting conditions for scientists studying the chemistry that leads to the development of life, NASA follows strict planetary protection protocols for the removal of the Dawn spacecraft. Unlike Cassini, who deliberately plunged into the atmosphere of Saturn to protect the system from contamination, Dawn will orbit Ceres, which has no atmosphere.

Engineers designed Dawn's final orbit to ensure it will not fail for at least 20 years – and probably decades more.

Rayman, who led the team that flew Dawn throughout the mission and is in its final orbit, likes to think of the end of Dawn as "a celestial monument inert to human creativity and ingenuity."

You will find more information on Dawn's mission legacy at the following address: https://dawn.jpl.nasa.gov/mission/toolkit/