ann19006 — Announcement

Asteroid Ryugu
4 February 2019
First Official Feature Names Approved for Asteroid Ryugu

The IAU Working Group for Planetary System Nomenclature has approved a number of names for selected features on asteroid (162173) Ryugu, all of which are names found in stories and fairy tales for children. The new names come from Asia, Europe, and North America.

Hayabusa-2 arrived at Ryugu in June 2018 and has since studied the asteroid from orbit and by landing small rovers on its surface. Immediately after arrival the Hayabusa-2 Team got in contact with the IAU and requested the start of the official naming process for the features on the surface of this asteroid.

The IAU Working Group for Planetary System Nomenclature is responsible for the official naming of the planets, their satellites, and the surface features on all celestial bodies in our Solar System. The naming procedure is implemented through a carefully prepared list of themes which aim to link the bodies and their surface features together. Since Ryugu itself is named after the dragon god’s undersea palace in Japanese folklore, the approved theme for its surface features has become “Names in stories and fairy tales for children”.

Hayabusa-2 showed that boulders were important prominent features on the surface of this asteroid. However, as boulders or rocks are generally considered to be “non-permanent” features they have so far not been eligible for naming. Therefore the IAU Working Group for Planetary System Nomenclature has decided to introduce a new descriptor term for this type of feature: “saxum” (saxa, plural) for boulders and rocks, and to accept proposals to name boulders or rocks on small planetary bodies, under the following conditions:

  1. The named object must be larger than 1% of the mean diameter of the body.
  2. The named object must have exceptional scientific significance, such as defining a specific longitude in the coordinate system, large size relative to the asteroid diameter etc.

The first 13 names officially approved by the IAU are listed below, along with a short summary of their origin and the descriptor of the named feature:

  1. Ryujin Dorsum: “Dragon god”, father of princess Otohime, master of the undersea Ryugu Palace (Japan)
  2. Urashima Crater: Fisherman who rescued a turtle and travelled on its back to the dragon Ryujin’s undersea Ryugu Palace, where he was welcomed by princess Otohime (Japan)
  3. Cendrillon Crater: Original name of the girl in European folklore often called Cinderella (France)
  4. Kolobok Crater: Small round bread, which ran away from home singing his tricky song (Russia)
  5. Brabo Crater: A brave young man who defeated a giant (Netherlands)
  6. Kintaro Crater: The child with super strength who grew up on Mt Ashigara (Japan)
  7. Momotaro Crater: The boy who came to Earth in a giant peach and fought a horned ogre (Japan)
  8. Kibidango Crater: Dumplings made from the flour of the kibi grain that Momotarou brought on his adventure (Japan)
  9. Tokoyo Fossa: Eternal timeless land across the sea or undersea kingdom, where the princess Otohime lives (Japan)
  10. Horai Fossa: Mythical paradise of the immortals (Japan)
  11. Catafo Saxum: Boy who cleverly marked a route to avoid losing his way (USA)
  12. Otohime Saxum: The princess who lived in Ryugu Castle and welcomed Urashima (Japan)
  13. Ejima Saxum: Seacoast where Urashima rescued the turtle and left for Ryugu Castle (Japan)



Rita Schulz
Chair IAU Working Group Planetary System Nomenclature/ESA
Tel: +31 71 565 48 21

Lars Lindberg Christensen
IAU Press Officer
Garching bei München, Germany
Tel: +49 89 320 06 761
Cell: +49 173 38 72 621

About the Announcement



Asteroid Ryugu