research highlights

ASTEROIDS Cometary Bennu? Mon. Not. R. Astron. Soc. Lett. 481, L49–L53 (2018)

Credit: NASA/Goddard/University of Arizona

Asteroid (101955) Bennu is the target of February and June 2018, covering phase NASA’s sample-return mission OSIRIS-REx angles between ~15° and ~60°. Among (the first image of the asteroid obtained by the asteroids with the same spectral the spacecraft is pictured). In anticipation behaviour as Bennu — known as B-types, of the rendezvous, which will happen in corresponding to primitive carbonaceous December this year, many Earth-based chondrites — only 3200 Phaethon has observations of the body have been been observed at such a wide range of performed. Such measurements will help phase angles. place the upcoming in situ measurement The results show that Bennu’s phase within the wider context of remote curve is more similar to that of comet monitoring of asteroids from Earth. Hale–Bopp than of Phaethon. Thus, Bennu Alberto Cellino and collaborators find might belong to a sub-class of near-Earth some unexpected behaviour by looking at objects with cometary characteristics or of Bennu’s polarimetry. cometary origin. The close-up observations Phase-polarization curves of asteroids, of OSIRIS-REx will determine if Bennu is which trace their polarization as a function actually a member of the elusive category of the Sun–asteroid–Earth angle (the of objects between standard asteroids and phase angle), help determine their surface standard comets. properties, such as the albedo or the grain size of their regolith layer. Cellino et al. Luca Maltagliati analyse seven polarization measurements of Bennu obtained by the FORS2 instrument Published online: 24 September 2018 at the Very Large Telescope (VLT) between https://doi.org/10.1038/s41550-018-0599-5

Nature Astronomy | VOL 2 | OCTOBER 2018 | 761 | www.nature.com/natureastronomy 761