How Do You Land on a Moon With Almost No Gravity?

Last August, looking up from the edge of an ancient river delta on Mars, the Perseverance rover’s electronic eye spied an oblong shadow crossing the distant, glowing Sun. Phobos, the Martian moon named for the Greek god of fear and panic, was transiting the solar disk. Too small to darken the pale, dust-tinged sky, but orbiting close enough to eclipse...