Asteroid ryugu: collected samples compared to probe data

  • Research
Published on April 29, 2022 Updated on April 29, 2022
Dates

on the February 23, 2022

ASTEROIDE
ASTEROIDE

Researchers from the Lagrange laboratory (CNRS – Université Côte d'Azur – OCA) and members of the scientific team of the Hayabusa2 mission (JAXA) have compared for the first time data taken by the probe as it collected samples from the asteroid Ryugu and data from the analysis of the samples brought back to Earth. Collected at two locations on the surface of Ryugu, these samples clearly reveal all the diversity and different characteristics of the material that constitute this primitive asteroid. The results are published in the journal Science.

The Hayabusa2 probe carried out two sample collections from the asteroid Ryugu in 2019, which brought back to Earth 5.4 grams of asteroid material from its surface and subsurface. During these two successful collections, numerous images were taken, making it possible to analyze in detail the interaction of the sampling device with the surface, the surface properties and the material ejected during the operation. These images were compared with those of the material brought back to Earth.  
 
Images of the material ejected during the sample collections and as the propulsion system activated to move the probe away from the asteroid's surface show that the ejected rock fragments have two types of morphologies: some have a rugged appearance, others have a smoother appearance. These two types are similar to the morphological variations observed by the probe in rocks across the whole surface and by the Franco-German (CNES-DLR) lander MASCOT (see Fig. 1), indicating that the material ejected during the collections is representative of the surface material in general. In addition, analysis of a sequence of the images shows that one of these ejecta fragmented by colliding with the probe. The researchers were able to determine that this collision occurred at a very low speed (around 0.1 m/s). However, the fragmentation of carbonaceous chondrite meteorites, used as analogues of Ryugu material, requires an impact velocity > 1 m/s. In agreement with the spectral data measured in situ by the probe, the Ryugu surface is therefore partly made of a very porous material with low mechanical strength.  
 
More than two hundred small lithic fragments (1 to 10 mm in size) taken from the two sample collection chambers have also been studied in terrestrial laboratories. Analysis of the structure, surface morphology, shape and color of these fragments indicates that they are similar to the Ryugu surface material observed by the probe. These results are important because they confirm that the samples were not affected by the process of collecting and returning them to Earth and do not suffer from any sampling bias. The samples have now moved on to the second phase of more detailed physico-chemical analyses, which will reveal the asteroid's rich geological history. This geological complexity of asteroids and the diversity of features observed on their surface continues to surprise researchers and represents a challenge to fully understand their origin.  
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ASTEROIDE

ASTEROIDE 2
ASTEROIDE 2

Figure 1: Top: (A) Image of the surface of Ryugu in the vicinity of the site of the first sample collection; (B) Similar image of the second collection site, near the crater produced by the impact of Hayabusa’s SCI (Small Carry-on Impactor), shown by a dotted line. These images were taken by the probe's wide-field navigation camera. The green arrows point to examples of rocks and flattened pebbles. The label type 1 corresponds to rocks with rough surfaces. The label type 2 corresponds to rocks with a smooth surface. The surface of the asteroid has a geological richness that surprised researchers and the diversity of pebbles present is well represented by the samples collected.  
Bottom: Two of the Ryugu samples brought back to the terrestrial laboratories, showing the same two types of morphology as those apparent in the images of the Ryugu surface. Type 1 is found in sample C0002 and type 2 in sample A0046.