Language: English Updated: 2025-11-20

162173 Ryugu

[[File:Hayabusa2 image of asteroid Ryugu (cropped and enhanced).jpg|thumb|upright|View of Ryugu from the Hayabusa2 spacecraft, showing its distinctive "spinning top" shape and boulder-strewn surface.]]

162173 Ryugu is a [[Near-Earth object|near-Earth asteroid]] of the [[Apollo asteroid]] group and a [[Potentially hazardous asteroid|potentially hazardous asteroid]]. It is a [[carbonaceous asteroid]] (C-type) approximately 1 kilometer (0.62 miles) in diameter. Ryugu gained significant scientific prominence as the target of the [[JAXA]] [[Hayabusa2]] sample-return mission.

Discovery and Naming

  • Discovery: Ryugu was discovered on May 10, 1999, by astronomers with the [[LINEAR program]] (Lincoln Near-Earth Asteroid Research) at the [[Lincoln Laboratory]]'s [[Experimental Test Site]] in [[Socorro County, New Mexico]]. Its provisional designation was 1999 JU3.
  • Naming: The asteroid was officially named "Ryugu" by the [[International Astronomical Union]] (IAU) on September 28, 2015. The name refers to [[Ryūgū-jō]] (竜宮城, "Dragon Palace Castle"), a magical underwater palace in Japanese folklore, from which the fisherman [[Urashima Tarō]] brings back a mysterious box. This name was chosen because the [[Hayabusa2]] mission, named after the [[peregrine falcon]], was designed to bring back samples from the asteroid, much like Urashima Tarō's return with a treasure from the Dragon Palace.

Orbital Characteristics

  • Classification: Ryugu is classified as an Apollo asteroid, meaning its orbit crosses Earth's orbit. It is also categorized as a potentially hazardous asteroid (PHA) due to its size and close approaches to Earth, though it currently poses no impact threat.
  • Orbit: It orbits the Sun at an average distance of approximately 1.19 [[Astronomical unit|AU]] (178 million km or 111 million miles) with an orbital period of about 1.3 years (474 days). Its orbit has an eccentricity of 0.19 and an inclination of 5.9 degrees with respect to the [[ecliptic]]. The orbital dynamics cause it to have occasional close encounters with both Earth and Mars.

Physical Characteristics

  • Shape and Size: Observations by Hayabusa2 confirmed Ryugu's distinctive "spinning top" or "diamond" shape, flattened at its poles and bulging significantly around its equator. Its average diameter is approximately 0.92 kilometers (0.57 miles), with dimensions roughly 1.07 km by 0.95 km by 0.95 km.
  • Surface Features: Ryugu's surface is extremely rugged and densely covered with numerous boulders of various sizes, ranging from a few centimeters to tens of meters across. Very few smooth areas are visible. A prominent equatorial ridge, informally named "Ryujin scales," is a key morphological feature. The surface also shows evidence of small craters and color variations, indicating differences in composition or exposure to space weathering.
  • Composition: Ryugu is a C-type (carbonaceous) asteroid, believed to be a remnant of the early solar system. Spectral analysis performed by Hayabusa2 indicates the presence of hydrated minerals, particularly phyllosilicates, which are indicative of past interaction with water. This suggests that Ryugu, or its parent body, experienced aqueous alteration. Its low bulk density (approximately 1.19 g/cm³) suggests a high porosity, consistent with a [[rubble pile]] structure.
  • Rotation: It has a relatively fast rotation period of approximately 7.6 hours. The "spinning top" shape is thought to be a result of its rapid rotation, where material migrates towards the equator due to centrifugal forces.

Hayabusa2 Mission

  • Overview: The [[JAXA]] (Japan Aerospace Exploration Agency) [[Hayabusa2]] mission was launched in December 2014 and successfully arrived at Ryugu in June 2018. It spent over a year orbiting the asteroid, conducting extensive remote sensing observations to map its surface and analyze its composition.
  • Surface Operations: During its stay, Hayabusa2 deployed multiple small probes onto Ryugu's surface:
    • Two [[MINERVA-II1]] rovers (named HIBOU and OWL), which successfully hopped across the surface.
    • The MASCOT (Mobile Asteroid Surface Scout) lander, developed by [[DLR]] and [[CNES]], which gathered data from several locations.
  • Sample Collection: Hayabusa2 performed two successful sample collection operations:
    • First Sample: In February 2019, the spacecraft briefly touched down to collect surface material.
    • Second Sample: In July 2019, Hayabusa2 deployed a small impactor to create an artificial crater. This allowed the spacecraft to collect subsurface material, which is thought to be less altered by space weathering.
  • Return: Hayabusa2 departed Ryugu in November 2019, returning its sample capsule to Earth in December 2020. The capsule landed safely in Woomera, Australia.

Scientific Significance

The samples returned from Ryugu represent pristine material from the early solar system, offering direct evidence of the building blocks from which planets formed. Analysis of these samples, ongoing in laboratories worldwide, is expected to provide unprecedented insights into:

  • The composition and characteristics of primitive asteroids.
  • The origin and evolution of water and organic matter in the solar system, potentially shedding light on the delivery of these essential ingredients to early Earth.
  • The processes that shaped asteroids, including aqueous alteration and space weathering.
  • The formation and evolution of the solar system as a whole.

[[Category:Near-Earth asteroids]] [[Category:Apollo asteroids]] [[Category:C-type asteroids]] [[Category:Hayabusa2 target asteroids]] [[Category:Objects discovered by LINEAR]] [[Category:Potentially hazardous asteroids]]

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