Assertion: asteroid | /r/HasProperty | visited by spacecraft
Facets:
Source sentences:
text: Eros was one of the first asteroids visited by a spacecraft, the first one orbited, and the first one soft-landed on.
text: The masses of asteroids are calculated from perturbations they induce on the orbits of other asteroids, except for asteroids that have been visited by spacecraft or have an observable moon, where a direct mass determination is possible.