NASA’s Dawn mission has shown us unprecedented detail in dwarf planet Ceres’ icy surface, but the adventure has only just begun.
After leaving massive asteroid Vesta in 2012, the ion engine-propelled robotic probe has been slowly homing-in on its second asteroid belt destination, becoming the first ever spacecraft to explore the asteroids that occupy a region between the orbits of Mars and Jupiter. Dawn is also the first probe to orbit two celestial bodies in the same mission — a feat made possible by its highly efficient mode of propulsion.
Last week, NASA scientists released the most detailed view of Ceres to date, better than even Hubble’s best observation of the small world. However, over the coming weeks as we look forward to orbital insertion in March, we can expect some historic science to be done as Dawn settles into its permanent new home.
During a special “Icy Worlds” media event at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., on Monday, Dawn mission scientists and engineers explained the need to explore the asteroid belt, specifically the two largest asteroids that, combined, account for 40 percent of the belt’s mass.
“These are baby planets,” said Dawn project manager Robert Mase. “They’re planets that started to form much in the same way our Earth started to form.”
During this early formation, Ceres and Vesta were prevented from achieving their full planetary potential, stifled by massive Jupiter “stirring the gravitational pot,” Mase explained. Instead, both Vesta and Ceres were stunted, destined to be protoplanets forever.
“Dawn was planned as a mission to go back in time to the beginning of the solar system … back to a time when the planets were forming,” said deputy principal investigator Carol Raymond.
Indeed, that is where the probe gets its name; Dawn is not named after some obscure and forced acronym, it’s named after its mission to explore objects that formed at the dawn of our solar system’s evolution, unlocking the mysteries of planetary formation, providing an insight to how Earth became the geological and biological oasis it is now.
Like the vast majority of space science disciplines, Dawn’s voyage of discovery started in the depths of space but ultimately leads back to working out how our planet formed and why it became so special.
Dawn’s Next Dance Partner
Getting to Ceres has been a celestial dance that started in 2007 at launch, eventually rendezvousing with Vesta in 2011 and now approaching Ceres.
“Basically what we’re trying to do now is to match the speed of Ceres going around the sun, so we’re slowing down, easing into orbit instead of a big crazy burn,” mission operations engineer Keri Bean told Discovery News. As opposed to more conventional chemical rocket engines, “we have an engine that’s slower, which takes lots of time.”
Dawn has three xenon ion engines that are used for propulsion, applying a steady rate of acceleration over a long period. As rapid acceleration and deceleration burns are not possible, a far more elegant approach to deep space navigation is required.
“We’re dancing around the solar system, and we’re in this dance with Ceres. We’ve danced with Vesta and now we’re going onto the next dance partner,” said Bean.
Interestingly, Dawn is carrying out maneuvers and science pretty much autonomously. As the spacecraft is so far away, it takes signals 1 hour to make a round trip from and to NASA’s Deep Space Network of radio antennae.
“We don’t have communication with the spacecraft most of the time,” mission director and chief engineer Marc Rayman told reporters at Dawn’s mission control center. “It’s a sophisticated and capable robot, far away in the solar system and it’s capable of performing functions on its own.”
“This mission isn’t for people who want instant gratification.”
As Dawn closes in on its ultimate dance with Ceres, however, the mission is rewarding NASA scientists’ patience, already hinting at some surprises.
Ceres’ New Moon
As the solar system’s innermost dwarf planet, the 490 kilometer (300 mile) wide world is warmer than the dwarf planets beyond the orbit of Neptune in the Kuiper Belt, Pluto’s domain. But Ceres is also known to be icy — far icier than its asteroid cousin Vesta. Therefore, scientists have studied Hubble’s best (yet blurry) photos of Ceres and interpreted the small world as having a comparatively smooth surface.
But as Dawn’s cameras are already showing us, Ceres is anything but smooth. There appear to be craters, varied terrain and a strange bright blob that has, so far, not been explained. But the best thing is that, very soon, Dawn will be transmitting sharper and sharper views of Ceres’ mysterious terrain and many of these questions may soon have answers.
However, Ceres will be Dawn’s final stop on its grand asteroid belt tour. When the probe’s hydrazine runs out (the fuel used by its positioning thrusters), the mission will be over and Dawn will become a permanent human-made moon and orbiting monument around Ceres.
“We’re going to stay at Ceres, we don’t have enough fuel to go anywhere else,” said Bean. “We have picked a very stable orbit, because of planetary protection, there’s the potential of water there; we don’t want to contaminate it.
“So we’re going to stay in a stable orbit around Ceres forever, so we’ll be a permanent moon. How cool is that!”