Our SpaceFlight Heritage: The decade of Dawn
When the Dawn mission finally launched on September 27, 2007, many saw it as practically miraculous. The spacecraft had survived numerous cancellations and delays, and it was only with concerted effort that the mission was reinstated. Dawn had an audacious mandate, to do something that hadn’t been attempted before – to travel to one body and then depart and head to another.
Originally slated for a June 20, 2007, launch date, the Delta II 7925H rocket from United Launch Alliance (ULA) tasked with carrying Dawn was delayed numerous times and for various reasons. The mission had originally been chosen as the ninth of NASA’s Discovery Program missions along with the agency’s Kepler space telescope in 2001.
Dawn‘s mission objectives were to characterize the conditions and processes of the Solar System in the earliest days of its formation and to better understand the role that size and water play in the evolution of planets and their formation by studying the two most massive of the protoplanets – Vesta and Ceres.
“Our interplanetary spaceship has exceeded all expectations in the last decade, delivering amazing insights about these two fascinating bodies,” said Dawn’s principal investigator Chris Russell, based at the University of California, Los Angeles.
After a nearly four-year cruise through space which included a Mars gravitational assist in 2009, Dawn arrived at Vesta in July 2011. Even prior to orbital insertion around the asteroid, Dawn had already begun to take images of the object from a distance of 745,645 miles (1.2 million kilometers).
For the next 14 months, the spacecraft made 1,298 orbits of Vesta at varying distances to fully map the object and gather scientific data on its composition and formation. What did Dawn find?
Canyons that dwarf the Grand Canyon, mountains twice the height of Mount Everest, and giant impacts to the world’s southern hemisphere. The spacecraft found a differentiated world formed at the very dawn of the Solar System, consisting of a nickel-iron core more than 133 miles (214 kilometers) wide, with an olivine mantle – components similar to Earth’s own interior.
Dawn found gullies where transient liquid water had once flowed after the subsurface ice had been melted due to surface impacts, along with other hydrated materials. It also found some of the largest troughs in the Solar System, some measuring more than 25 miles (40 kilometers) wide and 230 miles (370 kilometers) long.
“The science team is still actively exploring the troves of data that Dawn has delivered so far, comparing these two fossils of the early Solar System,” said Carol Raymond, Dawn’s deputy principal investigator.
Scientists now think that had Vesta not been drastically impacted by not one but two planet level impacts within the last 1 billion years, Vesta, too, would now be categorized as a dwarf planet beside Ceres and Pluto.
Each of these impact basins has carved out nearly one full percent of the mass of Vesta, blasting the fragments of the protoplanet out into space, some of which ended up raining back down onto Vesta’s surface. The remaining debris is thought to have become what are called V-type asteroids, some of which have landed on Earth as meteorites.
When these large southern craters on Vesta were studied, it appeared that whatever had impacted Vesta was able to cause a massive intrusion that extended throughout the entire crust and down into the mantle, ejecting olivine from the mantle onto Vesta’s surface.
“This continues to be a mission for everyone who years for new knowledge, everyone who is curious about the cosmos, and everyone who is exhilarated by bold adventures into the unknown,” said Marc Rayman, Dawn’s mission director and chief engineer.
Dawn switched gears in September 2012, leaving Vesta behind and heading toward Ceres. Long before Dawn achieved orbital insertion around Ceres, it had been making surprising discoveries, primary among these being a bright spot within the large Occator Crater on Ceres’ surface. The bright spot turned out to be many areas, the primary of these formations being Cerealia Facula – a central bright area with a dome at its center with fractures that appear to radiate away from it. This indicated to scientists that Ceres may have been geologically active in the recent past.
The 3-mile (5-kilometer) high Ahuna Mons is unlike anything else seen on Ceres. The “lonely mountain” is presumed to be a cryovolcano that erupted salty water at some time in the past. The geology in the area around Ahuna Mons suggests that liquid water may have once flowed on Ceres.
As Dawn continued its orbital reconnaissance of Ceres, the composition of the more than 300 bright areas on Ceres’ surface was determined to be salts – primarily sodium carbonate with smaller amounts of magnesium sulfate, ammonium chloride, and ammonium bicarbonate. Many of these areas were also associated with ammonia-rich clays. These salts are thought to have welled up from a possible subsurface layer of briny water, indicating that Ceres could be another of the ocean worlds.
Even after 1,595 orbits, Dawn continues to gather more data on Ceres; currently, it is in a 30-day elliptical orbit around the dwarf planet, collecting data on cosmic rays.
As was noted in Dawn of Small Worlds: Dwarf Planets, Asteroids, Comets by Michael Moltenbrey, Orbital ATK asked NASA to not give up on Dawn. In order to gain experience in a new market field, Orbital ATK offered to produce Dawn – at cost. They have since developed and built the I.C.O.N. and T.E.S.S. spacecrafts for NASA. ICON should be launched later this year, and TESS should is slated to fly in 2018.
“This is a proud day for every member of the Dawn team. Dawn has operated in deep space for ten years, returning masses of science data from the last two, large, uncharted worlds of the inner Solar System – Vesta and Ceres,” Joe Makowski, Orbital ATK’s Dawn Program Manager told SpaceFlight Insider. “The spacecraft has fulfilled the dreams of those who designed and built her, the people of Orbital ATK, JPL, and our mission and science partners around the world. Well done!”
Video courtesy of NASA’s Jet Propulsion Laboratory
A native of the Greater Los Angeles area, Ocean McIntyre's writing is focused primarily on science (STEM and STEAM) education and public outreach. McIntyre is a NASA/JPL Solar System Ambassador as well as holding memberships with The Planetary Society, Los Angeles Astronomical Society, and is a founding member of SafePlaceForSpace.org. McIntyre is currently studying astrophysics and planetary science with additional interests in astrobiology, cosmology and directed energy propulsion technology. With SpaceFlight Insider seeking to expand the amount of science articles it produces, McIntyre was a welcomed addition to our growing team.