Hayabusa2 to Visit Rapidly Spinning Asteroid in Extended Mission

by Douglas Messier
Managing Editor

JAXA has selected a second asteroid for Hayabusa2 to explore after the spacecraft completes its primary mission to Ryugu in December. But, it’s not going to be an easy destination to reach.

Hayabusa2’s extended mission will involve a flyby of another asteroid and two flybys of Earth before its rendezvous with asteroid 1998 KY26 in July 2031.

Engineers will need to keep the spacecraft’s systems, instruments and ion engine healthy for another 10.5 years. Hayabusa2 was launched almost six years ago on Dec. 2, 2014.

The asteroid’s small size — about 30 meters in diameter — could also make the rendezvous challenging for the aging spacecraft. The target also rotates on its axis roughly every 11 minutes.

JAXA laid out its plan for Hayabusa2’s extended mission during a recent press briefing. The information in this story is based on the English-language presentation.

Where to Next?

Hayabusa2 is set to complete its primary mission on Dec. 6 when a return capsule parachutes into Australia with soil samples from Ryugu. That will leave JAXA with a healthy spacecraft brimming with instruments configured to study asteroids.

JAXA considered sending the spacecraft to rendezvous with asteroid 2001 AV43. The elongated object is about 40 meters in diameter, and it takes 10.2 minutes to rotate on its axis and 383 days to orbit the sun.

Hayabusa2 would need to make a flyby of Venus and two flybys of Earth before its rendezvous with 2001 AV43 in April 2030. However, a Venus flyby would expose Hayabusa2’s systems and its ion engines to unacceptably high temperatures, JAXA said.

The space agency decided 1998 KY26 offered an attractive target that would place far less stress on the spacecraft during its decade-long voyage.

A Small, Spinning World

NASA’s Goldstone deep space facility in California used X-band radar to image 1998 KY26 when it passed Earth at a distance of 806,000 km on June 8, 1998. The images provided scientists with some basic information about Hayabusa2’s new target.

At about 30 meters in diameter, 1998 KY26 is roughly 1/30th the size of Ryugu. The small asteroid rotates on its axis every 10.7 minutes and takes 500 days to circle the sun.

Spherical in shape, 1998 KY26 is believed to be a C-type (carbonaceous) asteroid composed of a large amount of carbon as well as rocks and minerals. Measurements taken from Earth indicate the asteroid might contain water.

JAXA said 1998 KY26 will be interesting to compare to Ryugu and Bennu, which are larger C-type asteroids. NASA’s OSIRIS-REx sample return spacecraft is now in orbit around Bennu.

Hayabusa2 will measure 1998 KY26’s rotation and take images of it in the visible, near- and mid-infrared spectrums. It will be the first close-up observation of a rapidly-spinning asteroid.

“It is expected that the world’s first proximity observation of celestial bodies less than 100 m[eters] in diameter will provide useful information, not only for elucidating the history of the Earth but also for Planetary Defense,” JAXA said in its briefing document.

A Second Asteroid & More Science

Before it reaches 1998 KY26, Hayabusa2 will conduct a close flyby of asteroid 2001 CC21 in July 2026. The 700-meter wide object is believed to be a relatively rare L-type asteroid with a strong reddish spectrum. It rotates every 5 hours and takes 383 days to circle the sun.

During Hayabusa2’s decade-long extended mission, scientists will use the spacecraft’s small-aperture optical navigation camera (ONC) to conduct a search for exoplanets around bright stars.

Scientists will use the ONC to observe how stars dim as planets rotate around them. JAXA expects Hayabusa2 to conduct the first exoplanet observations ever made by a Japanese spacecraft.

Hayabusa2 will also make zodiacal light observations during its extended mission. This light is created when interplanetary dust particles measuring 0.1-100 micrometers scatter sunlight.

“It is important to explore the distribution and origin of
interplanetary dust through observations of zodiacal light in order to understand the whole picture of material transport through the Solar System: the
scientific goal of Hayabusa2,” JAXA said.

Hayabusa2’s three flybys of Earth will be used for this research.

“We aim to clarify the density and structure of interplanetary dust near the Earth by observing zodiacal light at multiple points away from the Earth,” the agency added.

JAXA noted that zodiacal light observations beyond the Earth’s orbit have not been conducted since NASA launched the twin Pioneer spacecraft in the early 1970s.