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Table 8 Properties of Ryugu, covered and discussed in the text

From: Asteroid Ryugu before the Hayabusa2 encounter

Global properties

 Measured

Eccentricity

0.190208

 

Semi-major axis

1.189555

AU

Inclination

5.883556

°

Period

473.8878

Days

Perihelion

0.963292

AU

Aphelion

1.415819

AU

Rotation period

7.6326

h

Pole direction in ecliptic coordinates (lambda, beta)

(310–340, − 40 ± 15)

°

Shape

Almost spherical

 

Volume-equivalent diameter

850–880

m

Phase function (Lommel-Seeliger model)

see Table 2

 

Geometric and bond albedos

see Table 3

 

Spectral type

C-type, see also Table 4

 

 Derived

Composition (meteorite spectral counterpart)

heated CM, CM2, or CI

 

 Predicted

Satellite

no

 

Dust around Ryugu

no or little

 

Boulders: power law exponent of cumulative SFD

− 3

 

Crater density

more than Itokawa, less than Toutatis

 

Surface roughness at meter scales

like Eros and Itokawa

 

Origin

Originated in the inner main asteroid belt, between ~ 2.1 and 2.5 AU, and reached the ν6 by inward Yarkovsky drift

 

Regolith thermophysical properties

 Measured

Thermal inertia

150–300, typically 200

J m−2 s−1/2 K−1

Maximum surface temperature

320–375

K

Roughness (the rms of surface slopes)

< 0.1

 

 Derived

Regolith thermal conductivity

0.020–0.108, most likely 0.042

W m−1 K−1

Typical particle size in diameter

3–30 most likely 6–10 (2.2–5 by Gundlach and Blum 2013 model)

mm

 Predicted

Regolith heat capacity at 300 K

758

J kg−1 K−1

Regolith emissivity

0.9

 

Regolith thermal albedo

0.019

 

Regolith bulk density

1100–1500

kg m−3

Regolith mechanical properties

 Predicted

Regolith porosity

~ 0.4–0.5

 

Regolith cohesion

100

Pa

Regolith angle of friction

33

°

Regolith tensile strength

< 1000

Pa

Inter-grain friction angle

40–50

°

Regolith bearing strength

< a few 1000

Pa

Compressive strength of rock

15–30

MPa

Tensile strength of rock

< 1

MPa

Presence of ponds

Possible, there are compositions being expected to be significantly different from that of the bulk asteroid

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