If the viking missions were such a rich source of information about mars, why have we sent the pathfinder, global surveyor, and other more recent spacecraft to mars? make a list of questions about mars that still puzzle astronomers.

Niobium forms a substitutional solid solution with vanadium. compute the number of niobium atoms per cubic centimeter for a niobium-vanadium alloy that contains 24 wt% nb and 76 wt% v. the densities of pure niobium and vanadium are 8.57 and 6.10 g/cm3, respectively

In positive numbers less than 1, the zeros between the decimal point and non zero are significant

Imagine that someone pushes one marble toward a motionless marble. would there still be action-reaction forces involved in the collision? how might the marbles’ motions be changed? ?