In deep space, there is very little friction. Once they launch a probe into deep space, where there are no external forces acting on it, scientists shut the probe’s engines off because the scientists want the probe to

Newton’s first law says that an object with no net external force keeps its velocity unchanged. With the engines off and no external forces acting on the probe, it will continue moving at the same speed and in the same direction. Therefore, the correct choice is D, move at constant velocity.

AI-written and checked against the verified answer.