Computer graphics show a small carry-on impactor firing a projectile into the surface of the Ryugu asteroid and the Hayabusa 2 probe collecting dislodged samples. (CG design by Masayuki Shirai)

The Hayabusa 2 space probe completed a three-and-a-half-year, 3-billion-kilometer journey to “spinning top” asteroid Ryugu, but now the hard part of its mission starts, the Japan Aerospace Exploration Agency (JAXA) said June 27.

“Frankly, I felt relieved,” Makoto Yoshikawa, mission manager and associate professor at the Institute of Space and Astronautical Science (ISAS) said of the probe’s arrival. “But there’s much more to come in the mission. The atmosphere here is tense.”

The Hayabusa 2 is scheduled to stay at Ryugu for about a year and a half, and land on the asteroid’s surface three times to collect samples before returning to Earth in 2020.

The samples could help solve some of the mysteries about how the solar system was formed. The samples could also contain organic substances that may help explain the origins of life.

The Hayabusa 2, which had been gradually slowing down, was operating normally and moving parallel about 20 km above Ryugu at 9:35 a.m. on June 27, JAXA’s project team confirmed at the ISAS control room in Sagamihara, Kanagawa Prefecture.

The Hayabusa 2 is the successor of the original Hayabusa probe, which returned to Earth in 2010 from the Itokawa asteroid. Although the mission was plagued with problems, the Hayabusa managed to bring to Earth the first-ever particles from an asteroid.

The Hayabusa 2 carries improved ion engines and communication equipment.

After being launched from the Tanegashima Space Center in Kagoshima Prefecture in 2014, the probe circled the sun and used the Earth’s gravity to propel it toward Ryugu, which passes near the orbits of Earth and Mars.

Although the asteroid is 300 million km from Earth, Hayabusa 2 covered 10 times that distance on its orbital journey.

After examining the geography and gravity of the minor planet, Hayabusa 2 is expected to land on Ryugu for the first time in autumn to collect samples from the surface.

Hayabusa is then scheduled to fire a metal fragment to create a hole in the surface and collect samples from inside the asteroid for the first time in history.

Ryugu’s shape resembles a spinning top and measures 900 meters in diameter. Its spin is relatively slow, taking about seven and a half hours for one rotation.

The asteroid’s surface is bumpy and features craters up to 200 meters in diameter.

Ryugu is believed to have emerged 4.6 billion years ago when the solar system was formed and may contain some of our world’s original building blocks.