Just in from JGR:Planets (Journal of Geophysical Research), vol. 130, #10:
Onodera, K. Ino, Y. Tanaka, Satoshi et al. Elastic Properties of Returned Samples From Asteroid (162173) Ryugu Art. e2025JE008944 2025JE008944
Short version: the authors measured the stiffness of Ryugu grains, and give their results.
Long version: Onodera et al. got the speed of sound (both P- and S-waves) of two particles returned by the Hayabusa2 probe, from asteroid (162173) Ryugu. By comparison, meteorite material (CI chondrites, and the Tagish Lake meteorite) was measured too. They saw that Ryugu material is broadly similar, yet not quite- it’s a bit softer. The most likely explanation is a different Ryugu formation history, though the authors admit two particles is a small number of particles- they may have picked odd ones.
Why is this important? Generally, P- and S-waves determine the effects of earthquakes (astero-quakes?). We know asteroids experience impacts, landslides, eruptions, and other dynamics, so knowing the material properties of one asteroid (hopefully not the last) gives us a better understanding of rubble-pile physics. It’s not intuitive that a pile of rubble on Earth will act like a rubble-pile asteroid in space. Specifically, Hayabusa2 performed the SCI (Small Carry-on Impactor) experiment, where an explosive charge created an artificial, witnessed crater event on Ryugu. But the SCI crater did not perfectly match predictions- why? A better understanding of Ryugu’s properties can only help. And specifically for the future, it may (…eventually, will) be necessary to deflect an incoming Earth impactor. The better we know the material properties and behaviors of asteroids, the better we will perform that deflection, with fewer uncertainties and risks. We already saw this with DART.