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

"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?

• Give JAXA some time to collect and process their data. The papers about 25143 Itokawa were published 8 months after the Hayabusa 1 encounter. – Mike G Jul 8 '18 at 13:43
• @MikeG: okay, then the question can just wait for the answer to become available. – SF. Jul 8 '18 at 14:19
• There is a special session on Hayabusa2 at the Division of Planetary Sciences 50th meeting in October. I would expect the first preliminary science results to be announced there but the data analysis takes time. Volume ans Mass in particular take a while as you have to make sure you've mapped all the surface of the asteroid and sampled the variable gravity field – astrosnapper Jul 27 '18 at 16:21

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 $$0.377 {\rm km}^3$$, 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 $$4.50\times 10^{11} {\rm kg}$$, with an uncertainty of 1.3%, mainly because of uncertainties in the solar radiation pressure on the spacecraft.