Curious. That doesn't gel with what I've read. For example, in this Wikipedia entry:

> "The Didymos system is not an Earth-crossing asteroid, and there is no possibility that the deflection experiment could create an impact hazard."

Further, in this preliminary presentation (PDF) by the planners of the DART mission, and in their subsequent paper (PDF), there's no mention of the system's binary nature being selected specifically for safety. The ease of measurement afforded by it being binary and its well understood parameters are the reasons given.

It's a shame Science Magazine didn't include a reference for the claim:

> "Didymos served as a gravitational anchor during impact, ensuring that Dimorphos wasn’t inadvertently ricocheted toward Earth."

To avoid future misunderstanding, I'd love to see a more direct reference for that if you know of one!