Taking a break from its usual night job hunting exoplanets, SPHERE data helped astronomers characterise the double asteroid. In particular, it is now possible to measure whether the smaller satellite has the same composition as the larger object.
While 1999 KW4 is not an impact threat, it bears a striking resemblance to another binary asteroid system called Didymos which could pose a threat to Earth sometime in the distant future.
Didymos and its companion called “Didymoon” are the target of a future pioneering planetary defence experiment. NASA’s DART spacecraft will impact Didymoon in an attempt to change its orbit around its larger twin, in a test of the feasibility of deflecting asteroids. After the impact, ESA’s Hera mission will survey the Didymos asteroids in 2026 to gather key information, including Didymoon’s mass, its surface properties and the shape of the DART crater.
The success of such missions depends on collaborations between organisations, and tracking Near-Earth Objects is a major focus for the collaboration between ESO and ESA. This cooperative effort has been ongoing since their first successful tracking (https://www.eso.org/public/announcements/ann14004) of a potentially hazardous NEO in early 2014.