As magnetic fields can influence planetary formation processes like dust accretion, it is important to understand which solar system objects had a magnetic field and which didn’t. Of the six asteroids where measurements have been attempted, four have shown no evidence of detectable magnetism.
Ryugu, recently visited by the Japanese spacecraft Hayabusa2 and its lander MASCOT (developed by DLR and CNES), may be different. It is spectroscopically similar to carbonaceous chondrite meteorites that have shown evidence of ancient magnetic fields.
Hercik et al.  report the first-ever magnetic measurement made at the surface of a carbonaceous asteroid like Ryugu. MASCOT did not detect a global magnetic moment, suggesting that the materials that constitute Ryugu do not contain substantial remanent magnetizations on decimeter scale.
Hayabusa2 has since left Ryugu and is expected to return to Earth samples of the asteroid in late 2020. It will be important to search for evidence of primordial magnetizations at finer scale to better understand the history of this asteroid.
Citation: Hercik, D., Auster, H.‐U., Constantinescu, D., Blum, J., Fornaçon, K.‐H., Fujimoto, M., et al. . Magnetic properties of asteroid (162173) Ryugu. Journal of Geophysical Research: Planets, 125, e2019JE006035. https://doi.org/10.1029/2019JE006035
—Laurent G. J. Montési, Editor in Chief, JGR: Planets