Data from the Japanese interplanetary station Hayabusa2 indicate that fine-grained dust may exist on the asteroid Ryugu, which is part of the regolith and covers both boulders and large grains of soil. Ryugu was previously thought to be dustless.
Is there dust on asteroid Ryugu?
Near-Earth asteroid (162173) Ryugu has been studied in detail by the Japanese automatic station Hayabusa2, which not only took soil samples from the surface and from the near-surface layer of Ryugu but also studied the asteroid from orbit around it. The capsule with the samples, in turn, was delivered to Earth at the end of last year
Importance for science
This body is of interest to scientists not only because of its belonging to objects of the “rubble pile” type, which are formed as a result of the collision of two asteroids and the subsequent secondary accretion of debris but also from the point of view of the abundance of carbon compounds in their composition.
This is particularly important because this type of asteroids were the ones that could have hit Earth in the early days of the planet and thus, caused major global changes that could have created life.
Analysis of observations
A group of astronomers led by Deborah Domingue from the US Planet Institute published the results of the analysis of observations of the equatorial part of Ryugu carried out using the ONC camera and the NIRS3 near-infrared spectrometer installed onboard Hayabusa-2 in order to study the properties in more detail regolith.
Good conditions for observations
At the same time, observations were carried out when the Sun was behind the station, and Ryugu was in front of the apparatus, which created good conditions for illuminating the surface of the asteroid.
The features of the obtained spectra indicate that one or more of the following conclusions are inadmissible for describing the Ryugu regolith: the size of the regolith particles is larger than the wavelength of the incident light, the particle sizes are the same, or the granulometric composition of the regolith is limited in size.
At the same time, images of the asteroid’s surface clearly show the presence of regolith grains on the Ryugu surface, which may not completely cover the entire surface of the boulders, including particles several centimeters in size.
Previously the descent module MASCOT did not find any evidence of fine-grained dust, but boulders on asteroid Ryugu are very porous and can break down to form small grains that can accumulate and mix with coarser-grained regolith or even cover the grains themselves.
Dust on asteroid Ryugu?
Thus, in some areas of Ryugu, fine-grained (less than 45 micrometers) dust may exist, which is part of the granular regolith of the asteroid.
Future of Hayabusa2
Now, Hayabusa2 is flying to the near-Earth asteroid 2001 CC21, which it will reach in July 2026. After that, it will visit a third near-Earth asteroid around the end of the decade before it makes a final return to Earth.
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• Domingue, D. (n.d.). Spectrophotometric Properties of 162173 Ryugu’s Surface from the NIRS3 Opposition Observations. The Planetary Science Journal.
• Morota, T., Sugita, S., & Cho, Y. (2020, May 8). Sample collection from ASTEROID (162173) Ryugu by Hayabusa2: Implications for Surface evolution. Science.
• Phys.org. (2021, September 2). Examining asteroid ryugu in opposition to hayabusa2: A starkly lit distribution of dust and rock.
• Yokota, Y. (n.d.). Opposition Observations of 162173 Ryugu: Normal Albedo Map Highlights Variations in Regolith Characteristics. The Planetary Science Journal.