Astronomers observed a dread-inspiring object close to Earth a year and a half before NASA's Double-Asteroid Deflection Test (DART) altered the track of a space rock.
It was Apophis, an asteroid. NASA was concerned that this 1,100-foot-wide rock, which was just identified 18 years ago, could strike our planet in the near future and cause serious damage.
Fortunately, recent measurements made during Apophis' distant flyby of Earth in March 2021 showed that it won't cause any issues for at least a century.
A mission like DART could lessen the threat when the time comes.But a mission called ACROSS will need to know Didymos' exact location
in order to establish how the minor asteroid Dimorphos' collision on September 26 might also have altered the course that its larger partner, Didymos, follows around the Sun.
Astronomers have made a significant first step toward achieving this goal when they finally observed Didymos obstructing light from far-off stars.