Hayabusa2 arrived at Ryugu, so I can make comparisons of asteroid scales!
Super congratulations to Japan and the Hayabusa2 team for their successful arrival at asteroid Ryugu today! It's too late, California time, for me to write much, but I could not resist taking the latest and greatest image released by the team and using it to create a couple of my patented scale comparisons.
First of all, I was immediately struck by how similar the surface texture of Ryugu appears to Hayabusa's target Itokawa. The shapes of the two asteroids are obviously very different, but where Itokawa is rubbly, Ryugu's surface looks the same -- even the boulders max out at roughly the same size. Itokawa has weird smooth "seas" that Ryugu appears not to have, but Itokawa's otter-like shape creates bizarre gravity lows that won't exist on much more spherical Ryugu. I'm calling this to scale (ish) because my knowledge of the scale of the two images isn't as precise as I'd like it to be. If I track down better scale information, I'll replace this with a modified version.
Images: JAXA, University of Tokyo, Koichi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu and AIST. Comparison: Emily Lakdawalla, The Planetary Society. All errors hers.
Itokawa and Ryugu compared
The two target asteroids of Hayabusa and Hayabusa2, compared. The comparison is based on less-than-precise information on the scales of the two images; it may be updated with another version once better scale information is available. Do not use for spacecraft navigation.
Okay, so how does Ryugu compare to other asteroids we've visited? Don't laugh, but we really didn't need to be as close as 20 kilometers away from it to be able to compare its shape to other worlds. (Bennu is on here also, currently represented by a dot until OSIRIS-REx arrives later this year.)
Montage by Emily Lakdawalla. Data from NASA / JPL / JHUAPL / UMD / JAXA / ESA / OSIRIS team / Russian Academy of Sciences / China National Space Agency. Processed by Emily Lakdawalla, Daniel Machacek, Ted Stryk, Gordan Ugarkovic.
Asteroids and comets visited by spacecraft as of June 2018, in color, excepting Vesta
A montage of 17 of the 18 asteroids and comets that have been photographed up close as of June 2018, when Hayabusa2 arrived at Ryugu. This version is in color but does not show the bodies at their correct relative albedo or brightness. Not included are Vesta or Ceres, both of which are many times larger than Lutetia. This is a provisional version for 2018. Bennu is currently represented by a gray dot; later in the year, that dot will be replaced by a new OSIRIS-REx image, and this image will be updated.