# Do we finally have a decent set of parameters of 162173 Ryugu?

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"Give a man a watch and he will know the time; give him two and he will never be sure" - this was my impression when reading the Wikipedia article on 162173 Ryugu.

Mean diameter:

• 0.865±0.015 km[3]
• 0.87 km[4]
• 0.90±0.14 km[5]
• 0.92±0.12 km[6]
• 0.980±0.029 km[7]
• 1.13±0.03 km[8]

And no mass estimates at all.

Now that Hayabusa2 has arrived, do we have solid measurements of Ryugu's size and mass yet?

A science paper from 2019 by K. Kitazato et al. shows a shape model of the surface in Fig. 2, so we now indeed know the exact size and the exact mass, even the surface temperature distribution:

The quoted paper refers to S. Watanabe et al., Science, 2019 which has all the details

Ryugu has an oblate body, with an equatorial radius of 502 ± 2 m and polar-to-equatorial axis ratio of 0.872 ± 0.007. The total volume obtained from the SPC-based shape model is $$0.377 { m km}^3$$, with an uncertainty of 1.3%. We conducted a gravity measurement during a spacecraft ballistic descent down to 0.85 km from the asteroid surface and a subsequent ballistic ascent up to 5.4 km. The estimated mass is $$4.50 imes 10^{11} { m kg}$$, with an uncertainty of 1.3%, mainly because of uncertainties in the solar radiation pressure on the spacecraft.

The highlighting in the quote is from me.