- NASA launched an ion-propelled probe called Dawn toward the asteroid belt in 2007.
- In 2015, Dawn reached Ceres, a Texas-sized dwarf planet that may hide a salty ocean and possibly alien life.
- The spacecraft is almost out of fuel, and its mission may end between mid-September and mid-October.
- Researchers expect Dawn to stay in orbit for 20 to 50 years, but after that it may crash into Ceres.
NASA’s only robot exploring the asteroid belt is about to die, the space agency explained during a live event on Friday.
However, the Dawn probe pulled off a last-ditch manoeuvre this summer that is helping to create surface maps of a dwarf planet – information that may be used to land a future mission on the distant world.
Dawn launched in 2007 and became the first NASA mission to use superefficient ion thrusters. In its yearslong voyage through deep space, the robot ended up in the asteroid belt, the mysterious and expansive zone between Mars and Jupiter. There, it has studied the region’s two largest objects: Ceres and Vesta.
Dawn reached Vesta first, in July 2011. Researchers think of Vesta, the second-largest object in the asteroid belt, as a “time capsule” for planet formation, since it failed to grow into something larger after the solar system’s birth.
After a year of exploration at Vesta, Dawn ion-propelled itself toward Ceres, a Texas-sized dwarf planet, where it arrived in March 2015. Ever since then, Dawn has made several major discoveries about the 592-mile-wide ice ball, including an ice volcano, shiny salt deposits, and other features that suggest a giant ocean may hide beneath the world’s cratered crust – possibly one that could harbour alien microbes.
NASA has since used up most of Dawn’s remaining fuel to slip into an orbit that zooms within 22 miles of Ceres’ surface about once a day.
These flybys are about 10 times as close as the International Space Station orbits above Earth and have led to the sharpest, clearest images of the dwarf planet yet.
“This orbit was like putting your glasses on if you don’t see very well – all of the sudden, all of this rich detail is popping out,” Carol Raymond, Dawn’s principal investigator and a planetary scientist at NASA’s Jet Propulsion Laboratory, said during the press event on Friday. “It will give us some insight as to what’s going on with the plumbing system under the surface.”
However, these unprecedented images and other data have come with a cost: a death for Dawn before the end of the year.
Why Dawn is now doomed
Using up Dawn’s fuel to achieve such a close orbit has essentially stranded the spacecraft at Ceres.
“The current orbit should be stable for 50 years,” Mark Sykes, the director of the Planetary Science Institute and a scientist on the Dawn mission, told Business Insider in an email. “There is no desire to change the orbit – and no juice.”
Dawn uses its “juice” to keep itself powered and talking to NASA. So using up the last propellant will forever silence the probe.
“It will struggle for a short time, but it will be impotent,”Marc Rayman, Dawn’s mission manager and chief engineer, wrote in a blog post on August 22. “Unable to point its electricity-generating solar panels at the sun or its radio antenna to Earth, the seasoned explorer will go silent and will explore no more. Its expedition will be over.”
Rayman said on Friday that Dawn might go silent within a month or so.
“We can’t determine that with exquisite accuracy,” he told Business Insider during the press event, adding that it was likely to run out of propellant (and stop talking to Earth) “sometime in the middle of this month to the middle of October.”
But the team, while sad about the probe’s coming demise, is counting its blessings, since the expedition was supposed to last nine years but has been going for nearly 11. Plus, Dawn continues to take high-resolution images of the surface once every 27 hours.
Once the probe runs out of fuel, it won’t spiral down and crash into Ceres for at least 20 years. In fact, Rayman said, the team’s analysis shows a “greater than 99%” chance that Dawn will stay in its current orbit for half a century, “and most likely longer than that.”
NASA wants to bring a sample of Ceres back to Earth
Rayman said the 20-year no-crash minimum was a core requirement of the Dawn mission.
That’s because NASA’s planetary protection office, which tries to prevent contamination of other worlds by microbes from Earth, thinks two decades should be enough time for the agency to mount another mission to Ceres. A new probe could then look for signs of life without worrying about contamination by any microbes from Earth stuck to Dawn when it crashed.
“Ceres represents a place in the solar system that we’re interested in for future astrobiological exploration,” Rayman said. “If NASA chooses to mount a follow-on mission to conduct subsequent astrobiological exploration, it’s long enough to without being compromised by Dawn.”
Jim Green, NASA’s chief scientist, said the agency had pulled together working groups to come up with a plan to send a robot to the surface of Ceres, possibly near a vent, where it could probe salts and other materials – and maybe even send samples from the dwarf planet back to Earth.
“We’ll work out in the next decade whether one of those missions will indeed be going back to Ceres,” Green said on Friday.
The stakes are high as researchers discover more water and organic compounds elsewhere in the solar system – ingredients that may sustain rudimentary forms of alien life.
“We know there is an active geological cycle that’s bringing material from deep [inside] up to the surface,” Carol Raymond said. “That gives us an opportunity to sample some of Ceres’ internal material.”
As Dawn continues to rack up high-resolution images of Ceres’ surface, the argument for collecting a sample of the dwarf planet may be strengthened.
“The holy grail of any planetary-science mission is a sample return, but it’s also very difficult,” Raymond said. “With an object like Ceres, you really want to know where to sample.”
This story has been updated with new information. It was originally published at 1:27 p.m. ET on September 7, 2018.
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