The Hayabusa 2 spacecraft has completed its mission at asteroid Ryugu — including collecting samples — and is now journeying back to Earth.

Hayabusa 2
An artist's conception of Hayabusa 2 returning to Earth, late next year.

Most interplanetary missions end with the spacecraft simply falling silent on an alien world; a very few make the journey home. On Wednesday, November 13th, Japan's Hayabusa 2 spacecraft started such an adventure as it fired up its engines, leaving asteroid 162173 Ryugu for a long journey home with its precious cargo: samples of the asteroid.

The Japan Aerospace Exploration Agency (JAXA) reported that confirmation of the engine burn was received at 10:05 a.m. Japan Standard Time (8:05 p.m. EST on November 12th). The spacecraft's initial departure velocity was 9.2 centimeters (3.6 inches) per second. It will now take the spacecraft thirteen months to return to Earth.

“It's sad to say goodbye to Ryugu,” said Yuichi Tsunda (JAXA) during a briefing from spacecraft mission control center on Tuesday. “It has been at the center of our lives over the past one and a half years.”

Expect to see departure images coming from Hayabusa 2 as Ryugu recedes in the distance over the coming weeks.

Hayabusa 2: The Story Thus Far

Launched atop an H-IIA rocket from the Tanegashima Space Center on December 3, 2014, Hayabusa 2 is the successor to JAXA’s Hayabusa 1 mission, which explore asteroid 25143 Itokawa in 2005.

Hayabusa 2 made one Earth flyby for a gravitational assist on December 3, 2015, before arriving in Ryugu's vicinity in June 2018.

The spacecraft revealed Ryugu to be a rough diamond-shaped world, strangely similar to (but bigger than) the asteroid 101955 Bennu that's currently being explored by NASA’s Osiris-REX mission.

A raw image of asteroid Ryugu, from March 2019.

On September 21, 2018, Hayabusa 2 released the 1A and 1B asteroid rovers named HIBOU and OWL, which both tumbled to a landing on Ryugu. The German Aerospace Center’s MASCOT rover also landed in October 2018 and operated for more than 17 hours before falling silent. A third rover, MINERVA II-2, failed on deployment early last month.

Hayabusa 2 sample
Touchdown . . . Hayabusa 2's sampling maneuver on Ryugu.

The climax of the mission came on February 21, 2019, when Hayabusa 2 briefly touched down on the surface of Ryugu, fired a tantalum pellet at the asteroid's surface, and collected upward-flying material with its sampling mechanism. Next, the spacecraft  deployed several reflective target markers, then fired an explosive device at the asteroid on April 5, 2019. The spacecraft made a second sub-surface sampling maneuver from the resulting crater on July 11, 2019. While both sample collections went off without a hitch, we won't know how much was collected until the samples make their way back to Earth.

The Long Journey Home

Next up, Hayabusa 2 will fire its main ion engines in late December, putting it on track for a return to Earth late next year. Like Hayabusa 1, Hayabusa 2 will eject a 40-centimeter (16-inch) diameter sample return capsule as it flies by Earth in December 2020, for recovery on the Woomera Test Range in Australia.

The Hayabusa 2 spacecraft will remain in solar orbit, post-Earth flyby. The spacecraft will still have some spare xenon fuel left for its thrusters, extra propellant that was stored for contingencies, such as an extra sampling attempt. Researchers have suggested that the mission could be extended to flyby past asteroid 2001 WR1 in the June 2023 timeframe, but such an extension isn't official yet.

The position of asteroid Ryugu on January 1st
The position of asteroid Ryugu on January 1, 2020, relative to the earth.
JPL / Horizons

Hayabusa 2's sample return will represent a pristine piece of the primordial solar system, critical for telling us about early conditions that led to the origin of the inner, rocky planets. The first Hayabusa mission struggled to return minuscule shards of Itokawa to Earth . . . researchers hope that Hayabusa will return with a mother lode of material in comparison.

The return of Hayabusa 2 will be a top space story to watch in 2020.


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