The OSIRIS-REx spacecraft has been at Bennu since Dec. 3, 2018, mapping the asteroid in detail, while the mission team searches for a sample collection site that is safe, conducive to sample collection, and worthy of closer study. One of the biggest challenges of this effort is that Bennu has an extremely rocky surface and each boulder presents a danger to the spacecraft’s safety as it touches down and grabs a sample.
Source:
https://phys.org/news/2019-05-nasa-asteroid-mission-sample-site.html