Scientists celebrated another success with Japan’s Hayabusa 2 spacecraft on 11 July when the robot explorer accomplished a second pinpoint touch-and-go landing on asteroid Ryugu, this time to collect a sample of pristine dust and rock excavated by an explosive impactor earlier this year.
Using rocket thrusters to control its descent, and guided by a laser range finder, Hayabusa 2 glacially approached Ryugu on autopilot, slowing to a relative speed of about 10 centimetres per second (4-inches per second) in the final phase of the landing.
Hayabusa 2 manoeuvred over a bright navigation aid released on the asteroid’s surface earlier this year to mark the landing site, then went in for the final descent, with the probe’s sampling horn extending from the front of the spacecraft.
Telemetry data and imagery downlinked from Hayabusa 2 show the spacecraft briefly touched down on the asteroid at 0106 GMT (10:06 a.m. Japan Standard Time), and began climbing away from Ryugu seconds later, pulsing its thrusters to counteract the 900-meter-wide (half-mile-wide) asteroid’s feeble gravity.
At a press conference around four hours later, officials hailed the brief landing as a perfect success, following the mission’s first touch-and-go landing on Ryugu in February.
“Hayabusa 2 today executed a second touchdown, and we were able to obtain (information about) the history of the Solar System,” said Yuichi Tsuda, Hayabusa 2’s project manager at the Japan Aerospace Exploration Agency.
Ground teams cheered when data streaming back from the spacecraft, currently orbiting the sun in lock-step with Ryugu more than 244 million kilometres (151 million miles) from Earth, confirmed the touchdown.
Launched in December 2014, Hayabusa 2 is Japan’s mission to travel to an asteroid and collect samples for return to Earth. Scientists are eager to analyse specimens from Ryugu, a dark asteroid rich in carbon, a critical building block of life.
Researchers will study the samples for clues about the formation of the Solar System 4.6 billion years ago, and perhaps the origin of water and life on Earth.
Mission managers last month decided to send Hayabusa 2 on a second sampling run to gather bits of rock and dust from a second location on Ryugu, providing scientists with more varied materials to examine when the mission returns to Earth late next year.
Hayabusa 2’s sampling mechanism works by firing a metal bullet into the asteroid once the probe’s sampler horn contacts the surface. The projectile is designed to force bits of rock and dust through the sampler horn into a collection chamber inside spacecraft.
Takanao Saiki, Hayabusa 2’s project engineer and flight director at JAXA, told reporters in a press briefing Thursday that data downlinked by the spacecraft showed the temperature rose in the projectile’s firing mechanism at the time of landing, suggesting the system functioned as intended.
Three images taken by a camera on-board Hayabusa 2 showed the sampling horn contacting the asteroid, then violently blasting away debris from the surface. Countless tiny asteroid fragments were visible around the spacecraft in the final snapshot in the three-image sequence released by JAXA.
“The third picture is really amazing,” said Makoto Yoshikawa, Hayabusa 2’s mission manager “It’s really awesome, a large amount of chips of rocks are flying off.”
“This is a wonderful picture, I think,” Tsuda said. “Hayabusa 2 touched the surface of Ryugu, so this is evidence.”
A different view of the landing site taken by Hayabusa 2’s navigation camera shows a cloud of debris left behind moments after the spacecraft took off from the asteroid.
With its second and final sample collection complete, Hayabusa 2 started to climb back to a “home position” roughly 20 kilometres (12 miles) from the asteroid. The spacecraft closed the lid to the sample catcher device containing the asteroid pay dirt, and ground teams will later send commands to seal it inside the re-entry canister that will carry the material through Earth’s atmosphere at the end of the mission.
“There’s nothing I need to complain about, everything moved perfectly,” Tsuda said through a translator. “It was a perfect operation, so … it’s a 1,000 score out of 100.”
Not only did the specimens gathered Wednesday come from a different location on Ryugu than the first sampling run, scientists say the newly-captured materials originated from underneath the asteroid’s surface, where they may have escaped radiation and other space weathering effects for billions of years.
The pristine samples were exposed during a daring, unprecedented bombing run by the Hayabusa 2 spacecraft in April. The probe deployed an explosive charge to fire into the asteroid at high speed, carving a fresh crater and ejecting buried materials around the impact site, ripe for retrieval by Hayabusa 2.
“We decided to obtain the samples in this particular area so that we would be able to sample the subsurface materials … and because our operation was perfectly conducted, therefore, we can observe that we obtained some subsurface samples,” said Seiichiro Watanabe, Hayabusa 2’s project scientist from Nagoya University.
“Bringing the subsurface materials (back to Earth) will be something no other country can do in the coming 20 years or so,” Watanabe said.
Hayabusa 2’s sampler carrier has three chambers to separate materials gathered from each landing. Officials decided to press ahead with the second sampling run after assessing the scientific benefits and engineering risks of the maneuver, but with two samples now on-board the spacecraft, mission managers do not plan to attempt a third sampling run.
While Hayabusa 2 explores Ryugu, NASA’s OSIRIS-REx mission is surveying asteroid Bennu before moving in to collect a sample there in 2020 for return to scientists on Earth in 2023.
OSIRIS-REx is designed to bring home at least 60 grammes (2.1 ounces) of samples from Bennu, significantly more than Hayabusa 2. But OSIRIS-REx is only expected to collect a single sample from one location on Bennu’s surface.
NASA and JAXA agreed in 2014 to share their asteroid samples.
Named for a dragon’s palace in a famous Japanese fairy tale, asteroid Ryugu completes one circuit of the Sun every 1.3 years. Its path briefly brings it inside Earth’s orbit, making Ryugu a potentially hazardous asteroid.
The orbit also made Ryugu an attractive candidate for a sample return mission.
The Hayabusa 2 spacecraft arrived at Ryugu in June 2018, and deployed three mobile scouts to hop around the asteroid’s surface last September and October, achieving another first in space exploration.
Hayabusa 2 will depart Ryugu in November or December and fire its ion engines to head for Earth, where it will release a re-entry capsule protected by a heat shield to land in Australia in December 2020.
“We have captured the samples,” Tsuda said. “We must make sure that it comes back to Earth, so we need to continue with the operations properly.”
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