Question

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 probes engines off because the scientists want the probe to
stop immediately.
speed up.
slow down.
move at constant velocity.

Explanation:

According to Newton's first - law of motion, an object in motion will stay in motion with a constant velocity in the absence of external forces. In deep space with no external forces acting on the probe after the engines are shut off, it will move at a constant velocity.

Answer:

move at constant velocity.