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The asteroid Ryugu shook at the impact of Hayabusa2



The asteroid Ryugu shook at the impact of Hayabusa2

The difference between the pre-impact surface DEM and the per-impact surface DEM around the impact point SCI. The color scale indicates the height of the surface morphology in meters, and a dotted semicircle shows the crater rim of SCI. Image Providers: Kobe University, JAXA, Tokyo University, Kochi University, Rikkyo University, Chiba Institute of Technology, Meiji University, Aizu University, AIST.

Professor Arakawa Masahiko (Graduate School of Science, Kobe University, Japan) and members of the Hayabusa2 mission have discovered more than 200 rocks ranging in size from 30 cm to 6m, newly emerging or moving due to Artificial impact crater created by Japanese spacecraft Hayabusa2̵

7;s Small Carry-on Impactor (SCI) on April 5, 2019. Some rocks have been disturbed even in areas far from the center of the crater fire 40m. The researchers also found that the seismic-rocking zone, in which the rocks on the surface are shaken and moved in an order of centimeters by the impact, extend about 30 meters from the crater’s center. Hayabusa2 recovered a surface sample at the northern point of the SCI crater (TD2) and the thickness of the sediment erupted at this site was estimated to be between 1.0 mm and 1.8 cm using Digital Altitude Map (DEM).


These findings on the resurfacing of a real asteroid could be used as a standard for simulating the number of small-body effects, in addition to the artificial effects on planetary missions. future chimpanzees such as NASA’s Double Asteroid Redirection Test (DART). AAS Planetary Science Board meeting on 30 October in session titled Asteroids: Bennu and Ryugu 2.

The purpose of hitting Ryugu with ~ 13 cm SCI bullets is to recover a sample of the material below the surface. In addition, this provides a good opportunity to study the surface renewal (resurfacing) processes due to the effect occurring on an asteroid with a surface gravity of 10.-5 gravity of the Earth. SCI succeeded in forming a crash crater, defined as an SCI hole with a diameter of 14.5 m (Arakawa et al., 2020), and the surface sample was recovered at TD2 (10.04 ° N , 300.60 ° E). It was found that the concentric region of the crater, four times the crater’s radius, was also disturbed by the SCI collision, causing the rock to move.

Researchers then compared surface images before and after the artificial impact to study the resurfacing processes involved in freezing, such as seismic shake and spray deposition. overflow. To do this, they constructed the SCI crater rim profiles using a Digital Altitude Map (DEM) including the pre-impact DEM subtracted from the post-impact DEM. The mean ring profile is approximately equal to the experimental equation of h = hrexp[-([-([-([-(r / Rrim-1) / λrim]and equipped parameters of Hr and merim 0.475m and 0.245m, respectively. Based on this configuration, the SCI crater’s coating thickness was calculated and found thinner than the usual result for natural craters, as well as calculated from the crater formation theory. . However, this discrepancy has been resolved by taking into account the effect of the rocks appearing on the post-collision image since the crater contours derived from DEM may not detect the rocks. This new one. According to this crater rim profile, the thickness of sediment erupting at TD2 is estimated to be between 1.0 mm and 1.8 cm.

The asteroid Ryugu shook at the impact of Hayabusa2

The map of cross correlation coefficient of the area around SCI crater overlaps the post-impact image. Cross correlation coefficients are described by color gradients on the map. The numbers and arrows indicate four projections that show a low cross-correlation coefficient. Image Providers: Kobe University, JAXA, Tokyo University, Kochi University, Rikkyo University, Chiba Institute of Technology, Meiji University, Aizu University, AIST.

The 48 rocks in the post-collision image can be traced back to their original positions in the pre-collision image and it is found that rocks as large as 1m have been ejected a few meters. They are classified into the following four groups according to their mechanism of motion: 1. digging currents, 2. thrust by a dropped object, 3. surface deformation pulled by slight motion of the Okamoto rock, and 4. seismic caused by the main SCI impact. In all groups, the motion vectors of these rocks appear to radiate from the crater center.

169 new rocks ranging in size from 30 cm to 3m were found only in post-collision images and they were distributed up to 40 meters from the crater center. The graph of the number of new rocks studied for each radial width of 1m at a distance of 9-45m from the crater center, with the maximum number of rocks found at a distance of 17m. Beyond 17m, the number of rocks decreases with increasing distance from the crater center.

The asteroid Ryugu shook at the impact of Hayabusa2

Distribution of the motion vectors around SCI crater. The arrows indicate the movement of each rock from its original position due to the effect of the applied force. Each color shows the distance moved as follows: purple 0-1 cm, blue 1-3 cm, green 3-10 cm, orange 10-30 cm and red 30-100 cm. Image Providers: Kobe University, JAXA, Tokyo University, Kochi University, Rikkyo University, Chiba Institute of Technology, Meiji University, Aizu University, AIST

To further investigate this, an assessment of the correlation coefficient between the images before and after the impact was performed. It was found that the area with a low cross-correlation coefficient outside the SCI crater has an asymmetrical structure, very similar to the area around the impact point where radioactive material is deposited (Arakawa et al. the, 2020). Based on the sample comparison method using the correlation coefficient assessment, the displacements of the rock with cross correlation coefficient above 0.8 are inferred with a resolution of ~ 1 cm. This suggests that these shifts can be caused by seismic tremors. The rocks were moved more than 3 centimeters in the vicinity of SCI crater. This disturbance spans an area up to 15 meters from the impact, with motion vectors radiating from the crater’s center. Disturbed areas 10 cm displacement persist in areas more than 15m from the center, however they appear as plaques several meters in size and randomly distributed. Furthermore, the direction of these motion vectors in distant regions is almost random and there is no clear evidence to suggest that the radial direction from the crater center.

Movements greater than 3 cm were detected over a distance of 15 m with a probability of more than 50% and between 15 m and 30 m with a probability of approximately 10%. Hence, Arakawa et al. proposal, in accordance with Matsue et al. Experimental results of (2020) show that the earthquake caused most of the rocks in the area to move with maximum acceleration 7 times greater than the surface gravity of Ryugu (gryugu). Furthermore, they also discovered that the impact moves the rocks at a maximum acceleration of 7gryugu and 1gryugu in about 10% of the area. Hopefully these results will provide future digital simulations of small-body collisions, as well as planetary missions related to artificial impacts.


Japan created the first man-made crater on an asteroid


More information:
Presented at the American Astronomical Society’s 52nd Annual Meeting of the Planetary Science Division (Session: ‘Asteroids: Bennu and Ryugu 2’), October 29, 2020.

Provided by Kobe University

Quote: Ryugu asteroid rocked by the impact of Hayabusa2 (2020, October 29) retrieved October 31, 2020 from https://phys.org/news/2020-10-asteroid-ryugu-shaken -hayabusa2-impactor.html

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