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Enjoy these beautiful pictures of the dwarf planet Ceres that NASA's Dawn spacecraft continues to bring home, as this tap will soon be dry.
Mission team members announced today (Sept. 7) that Dawn – the only probe to orbit two objects beyond the Earth-Moon system – will likely run out of fuel in the next month, between mid-September and mid-October.
When this happens, the venerable probe will lose the ability to orient itself as needed to study Ceres or transmit data to its controllers on Earth. Dawn will become a cosmic ghost orbiting the dwarf planet in silence for decades. [Photos: Dwarf Planet Ceres, the Solar System’s Largest Asteroid]
"Although sad to see Dawn's departure from our missionary family, we are extremely proud of her many accomplishments," said Lori Glaze, Acting Director of NASA's Planetary Science Division, on September 6. "Dawn's scientific and technical achievements will resonate throughout history."
Along the road
The $ 467 million Dawn mission launched in September 2007 was tasked with conducting a close reconnaissance of the two largest bodies of the asteroid belt: the 950 kilometers of Ceres and the protoplanet 530 kilometers wide. Vesta.
Scientists consider the relics of Ceres and Vestaas from the beginnings of the solar system – remains that have not been incorporated into larger worlds such as Mars and Jupiter. This explains the name Dawn, which is not an acronym.
Dawn arrived in Vesta in July 2011 and studied the object from its orbit until September 2012, when the probe took off for Ceres. Dawn arrived at this last destination in March 2015, becoming the first and, until now, the only spacecraft to have been in orbit around a dwarf planet. (NASA's New Horizons spacecraft zoomed on the Pluto dwarf planet in July 2015, but it was a flyby, no orbit was involved.)
Dawn was able to accomplish these exploratory feats thanks to its supercharged propulsion system, which generates a surge by expelling xenon ions from a nozzle. Dawn's engine is not very powerful – it would take about four days to probe to go from 100 to 100 km / h (0 to 100 km / h) – but the gear can reach tremendous speeds because it can pull permanently on these engines.
"That's what I like to see as an acceleration with patience," said Dawn's mission director and chief engineer, Marc Rayman, of NASA's Jet Propulsion Laboratory (JPL) in Pasadena. , in California. "This opens up destinations in the solar system that NASA would otherwise be unable to reach."
Dawn is not about to miss xenon, by the way. The fuel is low in hydrazine, the conventional propellant that powers the smaller Dawn shift propellers.
Scientific award
Dawn's work at Vesta and Ceres revealed many details regarding these two bodies as well as the early history of the solar system.
For example, Dawn's observations showed that the northern half of Vesta had a surprising profusion of craters, suggesting that the asteroid belt contained larger objects for a long time than the researchers had thought, have stated the members of the mission team. And Dawn's measurements confirmed that Vesta is the source of the meteorites howardite, eucritite and diogenite, a common family on Earth.
And then there is Ceres. The dwarf planet is much more icy than the dry and rocky Vesta, which strongly suggests that the two bodies were formed in very different places – Vesta closer, in the realm of rocky planets like Earth and Mars and Ceres further in the cold depths. where the ice could survive. (Ceres migrated to its current location.)
And Dawn has discovered a variety of interesting features on Ceres, including the mountainous Ahuna Mons mountain, high 3 km (4.8 km), and strange and bright speckled spots on the ground of many craters.
This mosaic of a light spot on the Ceres dwarf planet, known as Cerealia Facula, combines images captured by NASA's Dawn spacecraft at altitudes up to 35 km above the surface of Ceres. The mosaic is superimposed on a topography model based on images obtained at Dawn's low-altitude mapping orbit (240 miles or 385 km elevation). No vertical exaggeration has been applied.
Credit: NASA
Dawn's observations revealed that these bright deposits consist of salts such as sodium carbonate. Scientists believe that these salts were left after brackish water rose to the surface of underground reservoirs and evaporated into space. [Photos: The Changing Bright Spots of Dwarf Planet Ceres]
The deposits are young, so this activity has occurred very recently. Indeed, Ceres certainly keeps a little brackish liquid underground, said Dawn's principal researcher, Carol Raymond, also from JPL.
"We know that there is an active geological cycle that brings materials from the surface to the surface, which gives us the opportunity to sample some interior materials from Ceres by sending a mission to the surface. "said Raymond at the press conference.
NASA is already thinking about what a surface mission might look like, said chief scientist Jim Green at the event today. Nothing is on the books, but NASA has held meetings to start developing potential architectures, Green said.
"The body is so intriguing in many ways that we absolutely have to go back," he said.
Left in the air
Dawn's end-of-life plan is very different from the one NASA had designed for its Cassini spacecraft in orbit around Saturn.
Last September, the low-fuel Cassini was led to a fiery death in the atmosphere of the ringed planet, so that the probe never contaminates the moons of Saturn, Titan or Enceladus, able to support life as it is. we know it. Since the earth.
But Ceres has no appreciable atmosphere, cremation Dawn is not an option. Instead, the mission team will leave the probe in its current orbit around Ceres – a highly elliptical path that brings it closer to 35 kilometers from the surface and up to 4000 kilometers.
NASA guidelines on planetary protection require that Dawn do not crush on the icy surface of Ceres for at least 20 years, Rayman said in a recent post. This window gives NASA time to mount another mission on an uncontaminated Ceres, if the agency decides to do so.
Dawn's current orbit is stable enough to meet this requirement, noted Rayman today.
"Our analyzes give us a very high confidence – above 99% – [Dawn] will remain in orbit for half a century and probably more than that, "he said at the press conference.
Follow Mike Wall on Twitter @ michaeldwall and Google+. follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.
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