NASA’s Dawn spacecraft has been zipping through the Asteroid Belt for the better part of a decade. It discovered water on the giant asteroid Vesta and ice volcanoes on the surface of Ceres, the largest object in the belt. But now its time is coming to an end.
Last year NASA said that Dawn was running out of fuel. According to a from the agency, the spacecraft probably will shut down sometime in the next month or so.
Dawn launched back in 2007 and arrived in the belt in 2011. For a few years it orbited the large asteroid Vesta, and then in 2015 it arrived at Ceres, an asteroid so big astronomers thought it was a planet when it was discovered two centuries ago (it now shares the dwarf planet classification with Pluto).
Before Dawn's arrival, we had never seen these huge objects up close. It turns out they're full of surprises. During its long mission, Dawn made invaluable contributions to science including mapping the entire surface of both worlds, discovering water on Vesta, and discovering ice volcanoes on the surface of Ceres. Perhaps the most notable discovery Dawn ever made was discovering organic molecules on Ceres, meaning that the dwarf planet has at least some of the building blocks for life.
That 2017 study was huge news. Ceres has never had an atmosphere or any kind of dynamic events on its surface. It’s basically unchanged from when it was formed billions of years ago. For that reason, finding some organic molecules on Ceres suggests those molecules were probably present in the early days of the solar system, which in turn is a good sign for life elsewhere in the universe. That’s the main reason Dawn went to the Asteroid Belt in the first place: Ceres and Vesta are like time capsules from the early solar system, and studying them can tell us a great deal about what that era was like.
After three years observing Ceres, time is running out for Dawn. Early in the mission the spacecraft’s reaction wheels broke, which meant the only way Dawn could maneuver was by using its thrusters and propellant. At some time over the next few weeks, Dawn will of propellent. Then it will be stranded in space.
When that happens, NASA will have one last thing to take care of. It must make sure Dawn never lands on the surface of Ceres. Dawn is contaminated with Earth bacteria, and NASA needs to ensure that those bacteria are never spread to Ceres. To make this happen, Dawn will be placed into a stable orbit around Ceres before it runs out of fuel completely. Dawn will be able to stay in that orbit for many decades, until we decide to visit Ceres again.