Hayabusa and Hayabusa2: JAXA's Asteroid Sample Missions

Hayabusa and Itokawa

Hayabusa, also called MUSES-C, launched on May 9, 2003, on an M-V-5 rocket from the Kagoshima Space Center. ISAS, the institute within JAXA that runs space science missions, lists a mass of 510 kg and a full width of 5.7 m with its solar panels open. It reached Itokawa in September 2005 and made two landings in November 2005. Its return cruise began in April 2007, and the sample capsule came back to Earth in 2010.

Itokawa is a near-Earth asteroid of the Apollo group, about 0.33 km (1,080 feet) across by JPL's effective diameter, and an S-type that spins once every 12.1 hours. The mission's results were published in a special edition of the journal Science, a first for Japanese explorers, according to ISAS.

JAXA's science summary says the mission found Itokawa to be a rubble pile, the first direct evidence of such bodies. A rubble pile is a loose collection of rock and dust held together mostly by gravity, not a single solid boulder. The grains brought home matched LL chondrite meteorites, which linked an S-type asteroid to rocks found on Earth. They also showed heating of up to 800 °C (1,470 °F), with the likely heat source being the decay of aluminum-26. The names of these meteorite classes are explained in the article on the types of meteorites.

Hayabusa2 and Ryugu

Hayabusa2 weighs about 600 kg and carried an impactor to make a crater in the asteroid's surface. Ryugu is a C-type near-Earth asteroid, about 0.9 km (2,940 feet) across, which turns once every 7.6 hours, according to JPL's database. The S-type and C-type labels are explained in the guide to what asteroids are. The key dates from ISAS and JAXA are:

• December 3, 2014: launch on an H-IIA rocket from Tanegashima Space Center.
• June 27, 2018: arrival at Ryugu.
• February 22, 2019: first touchdown, collecting surface material.
• April 5, 2019: the impactor creates an artificial crater.
• July 11, 2019: second touchdown, collecting subsurface material.
• November 13, 2019: departure from Ryugu.
• December 6, 2020: the return capsule is recovered in Australia.

The crater gave access to material below the surface. After the impactor made it on April 5, 2019, the second touchdown on July 11 collected subsurface material, JAXA says. Rock beneath the surface has had less exposure to space than rock lying on top of it.

What the Ryugu sample showed

JAXA's first analysis found organic material, including amino acids, and water in the sample. The science summary says Ryugu also proved to be a rubble pile, which indicates it was once part of a much larger body. It adds that the grains hold hydrated minerals, and tiny liquid inclusions of water and carbon dioxide were found inside them. It says the sample's composition closely matches the Sun and CI chondrite meteorites, and that it holds a plethora of organics, including amino acids and all five primary nucleobases. Ryugu's sample showed no heating above 100 °C (212 °F), unlike Itokawa's grains.

A NASA and international team reported in Science on February 23, 2023, that Ryugu has a rich complement of organic molecules. NASA's summary calls them prebiotic organics, meaning chemicals that come before life, and says the amino acid results are mostly consistent with those seen in certain carbon-rich meteorites. About 30 mg (0.001 ounce) of the sample went to the international soluble organic analysis team.

NASA's own sample mission is covered in the article on OSIRIS-REx and Bennu, and JAXA's science summary compares all three asteroids.

Hayabusa2's extended mission

Hayabusa2 did not stop after the capsule drop. Its extended mission was planned to reach asteroid 2001 CC21, now named Torifune, in 2026 and the asteroid 1998 KY26 in 2031, according to ISAS and JAXA. Earth swing-bys are planned for 2027 and 2028 along the way.

The Torifune flyby took place on July 5, 2026. JAXA's July 30, 2026 release says closest approach was about 744 m (2,440 feet) from the asteroid's center, about 400 m (1,310 feet) from its surface, and 120 m (394 feet) from the target point. JAXA calls it the closest pass to a Solar System body among all flyby missions to date. A first size estimate from the flyby gives a major axis of about 840 m (2,760 feet), a minor axis of about 340 m (1,115 feet) and an average diameter of about 540 m (1,770 feet). JAXA says the distances and sizes may be revised if the shape model changes, and that the science data are still being analyzed.

JAXA says the flyby demonstrated control technology that could make a spacecraft collide with a small asteroid, a step forward for planetary defense. The broader picture of that work is in the article on planetary defense and the DART test.

The final target, 1998 KY26, is about 11 m (36 feet) across and turns about once every 5 minutes, according to ISAS. JAXA lists arrival for 2031.

Common mistakes and myths

Myth: Itokawa and Ryugu are the same kind of asteroid. Itokawa is an S-type whose grains were heated to 800 °C. Ryugu is a C-type whose grains were never heated above 100 °C.

Myth: Hayabusa2 brought back the biggest asteroid sample. Its 5.4 g was far above its 0.1 g goal, but NASA's OSIRIS-REx later reported a much larger bulk sample from Bennu, as covered in that mission's article.

Myth: finding amino acids means finding life. NASA calls these molecules prebiotic organics, chemicals that come before life. Their presence is not evidence of life.

Myth: the mission ended when the capsule landed. Hayabusa2 flew past Torifune in July 2026 and is on an extended mission toward 1998 KY26.

Frequently asked questions

When did Hayabusa2 return its sample?

The capsule was sent back on December 5, 2020, and recovered in Australia on December 6, 2020, according to JAXA. It held 5.4 g of material from Ryugu.

Why did Hayabusa2 make a crater on Ryugu?

JAXA used an impactor on April 5, 2019, to make an artificial crater. On July 11, 2019, the spacecraft collected subsurface material, which has been less exposed to space than the surface.

What is Torifune?

Torifune is the name given to asteroid 2001 CC21. Hayabusa2 flew past it on July 5, 2026, at about 744 m from its center, and JAXA estimates an average diameter of about 540 m.

Where is Hayabusa2 going next?

JAXA plans Earth swing-bys in 2027 and 2028, then a rendezvous with the small, fast-spinning asteroid 1998 KY26 in 2031. Check JAXA's Hayabusa2 pages for any schedule change.