1.   Flying low to foil early-warning systems, the robot craft were intended to spray clouds of aerosolized pathogens over unsuspecting enemies.

2.   With these robot craft, scientists hope to subject their neighboring planet to a battery of tests and observations that could begin to unlock some long-sought secrets.

3.   In the meantime, NASA is launching a robot craft toward Saturn in October.

4.   That would allow the robot craft to send back a beacon signal.