Ryugu.space

Near-Earth asteroid (C-type) · Apollo group

Ryugu

(162173) Ryugu · 1999 JU3

A dark, spinning-top rubble pile that gave Japan's Hayabusa2 mission 5.4 grams of pristine asteroid — and some of the most surprising chemistry ever brought to Earth.

Key factsYoung explorer's science kit picker
Ryugu at a glance
Object typeNear-Earth asteroid, Apollo group; spectral type Cb (carbonaceous)[3]
DiscoveredMay 10, 1999 — LINEAR survey, Socorro, New Mexico[3]
Named2015, after Ryūgū-jō, the Dragon Palace of a Japanese folktale[4]
Diameter≈ 0.9 km (896 m)[3]
ShapeSpinning top with an equatorial ridge, Ryujin Dorsum[4]
Mass≈ 450 million tonnes[4]
Bulk density≈ 1.19 g/cm³ — about half its volume is empty space[4]
Rotation period≈ 7.6 hours[3]
Geometric albedo≈ 0.045 — it reflects under 5% of the sunlight that hits it[3]
Distance from Sun0.96–1.42 AU (average ≈ 1.19 AU)[3]
Orbital period≈ 475 days (1.3 years)[3]
Orbital inclination≈ 5.9°[3]
Craters / boulders77 craters; about 4,400 boulders larger than 5 m[4]
SpacecraftJAXA's Hayabusa2 — arrived June 27, 2018; samples returned December 2020[5]
Sample returned5.4 grams (mission goal: 0.1 gram)[1]

Discovery and name

Ryugu was discovered on May 10, 1999, by the LINEAR asteroid survey in Socorro, New Mexico, and carried the provisional designation 1999 JU3.[3] It was named in 2015 after Ryūgū-jō, the magical underwater Dragon Palace in the Japanese folktale of Urashima Tarō. In the story, the fisherman returns from the palace carrying a mysterious box — much like Hayabusa2 returning with its sample capsule.[4]

Size and shape

Ryugu is about 900 meters across.[3] Like asteroid Bennu, it has a spinning-top shape with a pronounced equatorial ridge named Ryujin Dorsum.[4] Its bulk density is only about 1.19 g/cm³, and JAXA scientists concluded that it is a rubble pile with roughly half of its volume made of empty space.[4]

The surface is extremely dark, reflecting only about 4.5% of the sunlight that hits it.[3] It is covered with boulders — about 4,400 larger than 5 meters. The biggest, Otohime, measures roughly 160 × 120 × 70 m.[4]

Orbit

Ryugu is a near-Earth asteroid in the Apollo group, meaning its orbit crosses Earth's. Its distance from the Sun ranges from about 0.96 to 1.42 AU, and it completes one orbit every 475 days.[3] Its closest possible approach to Earth's orbit (its minimum orbit intersection distance) is only about 0.0005 AU — roughly 80,000 km — though that is a geometric measure, not a prediction of any encounter.[3]

Sun Earth (1 AU)Mars (1.52 AU) aphelion ≈ 1.42 AU perihelion ≈ 0.96 AU
Top-down orbit of Ryugu to scale, computed from JPL orbital elements (a ≈ 1.19 AU, e ≈ 0.191).[3] Earth and Mars orbits shown for comparison.[6]

Hayabusa2 at Ryugu

JAXA's Hayabusa2 launched on December 3, 2014, on an H-IIA rocket and arrived at Ryugu on June 27, 2018.[5] It dropped two tiny hopping rovers, HIBOU and OWL, on September 21, 2018, and the German–French MASCOT lander on October 3, 2018.[5]

On February 22, 2019, Hayabusa2 touched down and collected surface samples. On April 5 it fired a copper projectile to make the first-ever artificial crater on an asteroid, and on July 11 it touched down again to collect material from beneath the surface.[1] The capsule landed in Australia on December 6, 2020 (Japan time), carrying 5.4 grams of Ryugu — far more than the 0.1-gram goal.[1]

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Hayabusa2's scientists studied Ryugu with cameras, microscopes and rock samples. Answer five quick questions and we'll suggest hands-on science kits that let kids do the same — with links to browse current options.

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What the samples revealed

Ryugu's grains turned out to be rich in water-bearing minerals, with a measured water content of about 6.8% by weight, and chemically similar to the rare CI chondrite meteorites.[4] Scientists found 20 different amino acids, and in March 2023 they reported uracil (one of the bases of RNA) and vitamin B3.[4] In March 2026, researchers reported all five of the canonical nucleobases used in DNA and RNA.[4] Because the samples arrived in a sealed capsule, contamination on Earth was ruled out in a way that is not possible for meteorites.[4]

Hayabusa2's next stops

Hayabusa2 is still flying. Its extended mission flew past asteroid 98943 Torifune (2001 CC21) in July 2026 and is planned to rendezvous with the small, fast-spinning asteroid 1998 KY26 in July 2031.[5][1]

Read more

Hayabusa2's touchdowns and the first artificial crater on an asteroid

How a Japanese spacecraft landed twice on a boulder-strewn rubble pile, blasted a crater with a copper projectile, and brought home 5.4 grams.

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What the Ryugu samples revealed: water, amino acids and the building blocks of RNA

From hydrated minerals to all five nucleobases — the key findings from Ryugu's pristine grains.

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The rovers that hopped across Ryugu

HIBOU, OWL and MASCOT: how tiny robots explored an asteroid where gravity is too weak for wheels.

Read →

Sources

  1. Asteroid Explorer “Hayabusa2” — JAXA
  2. Hayabusa2 Project — JAXA
  3. Small-Body Database Lookup: 162173 Ryugu (1999 JU3) — NASA JPL Solar System Dynamics
  4. 162173 Ryugu — Wikipedia
  5. Hayabusa2 — Wikipedia
  6. Planetary Fact Sheet (orbit comparison) — NASA NSSDCA

Figures are rounded; where sources differ we note it. Spotted an error? Tell us.