TOKYO -- Culminating a journey that began three and a half years ago, the Japanese space probe Hayabusa2 has finally reached its target: the asteroid Ryugu, which is orbiting the sun approximately 180 million miles from Earth.
The Japan Aerospace Exploration Agency (JAXA) gave the time of arrival as 9:35 a.m. Japan time Wednesday.
Hayabusa2 is the follow-up to the first-generation Hayabusa space probe, and it expands on Japan's leading role in asteroid exploration with technologies that have steered it faithfully to an even farther-away destination.
But that was the easy part, and JAXA faces many challenges to accomplish the main point of the mission, which is to collect samples from Ryugu and bring them back home for analysis. The first challenge, coming up in September, will be to land the probe on the asteroid, but many more will follow in an adventure that will last until the end of 2020.
The rocks on Ryugu are thought to contain remnants of carbon and water from the time of the birth of the solar system 4.6 billion years ago. If the JAXA mission is successful, analysis of those rocks could help scientists answer questions about the formation of the solar system and the origins of life.
"We are standing at the entrance to a new stage of space science exploration," mission project manager Yuichi Tsuda explained at a news conference held by JAXA.
Ryugu has a diameter of roughly 900 meters and rotates once every 7.5 hours around an axis like a spinning top. The asteroid is pockmarked with crater-like indentations and is strewn with boulders. Scientists expected Ryugu to be around that size, but never imagined it would have a diamond-like shape. "When we first saw that shape, we realized how hard it would be [to land on the asteroid]," Tsuda admitted. "The gods weren't friendly, but I am confident we can make the landing."
The landing site on the asteroid will be selected in late August. The unevenness and slanting of the surface are problematic, and the gravitational force on Ryugu is unknown. The plan is to press a rod-like instrument against the surface and drop projectiles to kick up rocks for collection. JAXA will also need to decide where to drop down the robot probes carried on Hayabusa2.
The biggest question mark is the technology for digging a hole into Ryugu to collect subsurface rock samples. That part of the mission will take place in March-April of 2019 and will involve the use of an explosive charge to drive a metal projectile at a speed of 2km per second into the surface. The hole will expose materials that have remained in their original form, covered for all these millions of years, to sunlight and radiation.
These collected samples will return to Earth in a capsule at the end of 2020, and that capsule and its contents will need to withstand the heat of re-entry through the atmosphere.
Hayabusa2 has been designed to meet these challenges with the help of all-Japanese technologies forged in the fields of robotics and small appliances by NEC and other Japanese manufacturers.