The near Earth Asteroid Ryugu is to be visited in 2018 by the Hayabusa-2 spacecraft, which will land and take sample surfaces of an asteroid. Or is it a comet or an ultra small Ceres type dwarf planet or moon?
Ryugu is said to have a rounded shape compared to the duck like nature of most other asteroids and comets we have closely observed. It is also an Apollo asteroid.
The constraints for size, spin or thermal properties therefore heavily depend on the wavelengths of the observations. We find that the solution which best matches our data sets leads to this C class asteroid having a retrograde rotation with a spin-axis orientation of (...) in ecliptic coordinates, an effective diameter (of an equal-volume sphere) of 850 to 880 m, a geometric albedo of 0.044 to 0.050 and a thermal inertia in the range (...)
Based on estimated thermal conductivities of the top-layer surface in the range (...), we calculated that the grain sizes are approximately equal to between 1 and 10 mm. The finely constrained values for this asteroid serve as a ‘design reference model’, which is currently used for various planning, operational and modelling purposes by the Hayabusa2 team
Hayabusa-2 Mission Target Asteroid 162173 Ryugu (1999 JU3): Searching for the Object’s Spin-Axis Orientation (PDF)
With Asteroid 162173 Ryugu being more observed than comets such as comet 67P, perhaps it is and should be a rounded shape, similar to Ceres. Then again comet 67P was meant to be rounded, as it is a comet.
Asteroid Ryugu or comet or rocky body?
It is the rare spectral type Cg, having qualities of both a C-type asteroid and a G-type asteroid.
162173 Ryugu | wikipedia
Generally similar to the C-type objects, but contain a strong ultraviolet absorption feature below 0.5 μm. An absorption feature around 0.7 μm may also be present, which is indicative of phyllosilicate minerals such as clays or mica.
In the SMASS classification the G-type corresponds to the Cgh and Cg types, depending on the presence or absence (respectively) of the absorption feature at 0.7 μm. The G-type, C-type and some rare types are sometimes collected together into a wider C-group of carbonaceous asteroids.
G-type asteroid | wikipedia
The observed and detected geological features of Ryugu will be similar to other geology features found on the very physically different planets, moons and rocky bodies in our solar system such as asteroids and active asteroids (comets).
Hayabusa-2 and 162173 Ryugu UPDATE 2018
The 1km-wide space rock known formally as 162173 Ryugu belongs to a particularly primitive type of asteroid, and is therefore a relic left over from the early days of our Solar System. Studying it could shed light on the origin and evolution of our own planet.
But the asteroid's rough surface could make landing risky. "The surface of Ryugu is covered with boulders... The biggest of these, near the South Pole, is estimated to be around 130m - about the same as the height of the London Eye.
Even further on in the mission, the Japanese Aerospace Exploration Agency (Jaxa) plans to detonate an explosive charge that will punch a crater into the surface of Ryugu. Hayabusa-2 would then descend into the crater to collect fresh rocks that have not been altered by aeons of exposure to the environment of space.
Hayabusa-2: Japan sets date for spacecraft's asteroid touchdown | BBC