Newton's first law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. This is normally taken as the definition of inertia
Assuming no other forces acting on the probe, according to Newton's 2nd law, we can find the acceleration attained by the probe due to the thrust (assumed constant) as follows:
Since the probe started from rest, we can express the final speed applying the definition of acceleration, as follows:
We can solve for t (in seconds) as follows:
Since 1 day = 86400 s, we can find the time in days as follows: