The return visit to the Dimorphos asteroid two years after the historic collision marks the latest step in efforts to see whether an incoming small asteroid could, if needed, be deflected from Earth to prevent potentially widespread damage.A Falcon 9 rocket carrying the probe lifted off at around 10:53am local time (1453 GMT), according to a live webcast.The European Space Agency (ESA) selected Elon Musk's SpaceX for the launch to fill a gap in Europe's own access to space.Dimorphos is a moonlet of Didymos, which is defined as a near-Earth asteroid.DART (Double Asteroid Redirection Test) was a proof-of-concept mission designed to use a spacecraft to nudge a celestial object that might otherwise strike Earth.Dimorphos and Didymos do not pose an actual threat to Earth.The spacecraft collided on September 26, 2022, at about 14,000m/h (22,530k/h) into Dimorphos, roughly 6.8 million miles (11 millionkm) from Earth.Scientists said in March that the collision changed not only the small asteroid's path but its shape as well.Hera will conduct a post-impact survey of Dimorphos in order to help expand the US space agency's experimental collision two years ago into a repeatable strategy for planetary defence, according to ESA.There are more than half a million asteroids in the Solar System, of which over 25,000 are classified as near-Earth objects.Of these, more than 1,000 are in ESA's risk list, meaning that they merit close follow-up observations, according to the agency.