Closing out a year-and-a-half of exploration, surveys and sampling operations at asteroid Ryugu, Japan’s Hayabusa 2 spacecraft fired thrusters in a departure maneuver Wednesday and headed for Earth with specimens snatched from the asteroid’s dark and rocky surface.
The robotic spacecraft pulsed its control rockets Wednesday to begin moving away from asteroid Ryugu at approximately 0.2 mph (9.2 centimeters) per second, beginning a slow departure that will culminate in the activation of the probe’s ion thrusters to reshape its trajectory and target arrival at Earth in late 2020.
Ground teams at the Japan Aerospace Exploration Agency’s control center in Sagamihara, Japan, confirmed the departure maneuver at 10:24 a.m. Japan Standard Time (0124 GMT Wednesday; 8:24 p.m. EST Tuesday).
Hayabusa 2’s thrusters propelled the spacecraft away from a position roughly 12 miles (20 kilometers) from Ryugu. The spacecraft is programmed to collect a series of farewell images of the half-mile-wide (900-meter) asteroid through Nov. 18, when Hayabusa 2 will be more than 31 miles (50 kilometers) from Ryugu.
According to JAXA, the spacecraft will change its orientation beginning Nov. 18 to prepare for testing of the probe’s ion engines two days later.
Hayabusa 2 carries four ion thrusters, powered by electricity and fueled by xenon gas, to adjust the craft’s course through the solar system. The plasma engines produce low thrust, but can run for months at a time, making for a fuel-efficient propulsion system on deep space missions.
After verifying the performance of the ion engines, Hayabusa 2’s ground team will uplink commands to begin the mission’s return cruise phase after Dec. 3, commencing a year-long transit back to Earth.
Up to three ion engines will fire at one time during Hayabusa’s return cruise.
The departure maneuver Wednesday marked the end of Hayabusa 2’s stay at Ryugu. During its time at the asteroid, the Hayabusa 2 spacecraft performed two touch-and-go landings to collect samples for return to Earth, and delivered a series of mobile robots to scout the asteroid’s surface.
Scientists are eager to analyze the specimens, which they expect may contain organic molecules. Researchers believe asteroids like Ryugu, or a larger body like the one from which Ryugu split off, could have seeded Earth with materials necessary for life.
JAXA unveiled an updated logo for the Hayabusa 2 mission after Wednesday’s departure from Ryugu. The logo is green, symbolizing plant life on Earth.
“If the sample returned from Ryugu contains organics, we may understand how Earth gathered the raw materials for life,” JAXA said in a tweet. “This logo reflects that expectation!”
As of Wednesday, asteroid Ryugu was located around 156 million miles (252 million kilometers) from Earth.
Named for a dragon’s palace in a famous Japanese fairy tale, Ryugu completes one circuit of the sun every 1.3 years. Its path briefly brings it inside Earth’s orbit, making Ryugu a potential impact risk with Earth in the distant future.
The asteroid samples gathered by Hayabusa 2 are stored inside a return capsule, which will separate from the Hayabusa 2 mothership before plunging into Earth’s atmosphere, aiming for a parachute-assisted landing in the Australian Outback at the end of 2020.
The exact date of the sample return capsule’s landing has not been confirmed by JAXA. The schedule will depend on the exact date of the start of Hayabusa 2’s return cruise, and is subject to final negotiations between JAXA and the Australian government, according to Yuichi Tsuda, Hayabusa 2’s project manager at JAXA.
Hayabusa 2 carries samples collected from two locations on Ryugu.
The spacecraft performed two precisely-guided touch-and-go landings on the asteroid in February and July. The sample collection in July was targeted to acquire material excavated from beneath Ryugu’s surface by a high-speed impactor deployed by Hayabusa 2 earlier this year.
Scientists will retrieve the asteroid specimens for detailed analysis.
“If we have 0.1 grams (of material), we can do all the sample analysis, but we hope we will have much more,” said Makoto Yoshikawa, Hayabusa 2’s mission manager at JAXA, in September.
“We want to study the organic matter on Ryugu because we want to know the origin of life on the Earth, and we think Ryugu has original matter that became life,” Yoshikawa said. “So our main purpose is analysis of the organic matter on the surface of Ryugu.”
Hayabusa 2 arrived in the vicinity of Ryugu in June 2018 after a three-and-a-half-year journey from Earth. The spacecraft launched Dec. 3, 2014, aboard an H-2A rocket from the Tanegashima Space Center in southern Japan.
During its time at Ryugu, Hayabusa 2 released three mobile landers to hop around the asteroid. Two MINERVA-II landers, developed in Japan, and a larger robot named MASCOT managed by the German and French space agencies beamed back images and scientific data from Ryugu’s surface last year.
Hayabusa 2 deployed a final MINERVA-II lander last month, but the robot suffered a computer fault and did not return any scientific data, JAXA officials said.
Hayabusa 2 is Japan’s second robotic asteroid sample return mission.
The mission’s predecessor, Hayabusa, returned to Earth in June 2010 with microscopic specimens gathered from the surface of asteroid Itokawa, despite multiple technical failures with its propulsion and sample collection systems.
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