Cassini-Huygens flies by Venus, picking up a "gravity assist." Cassini-Huygens is a massive spacecraft, loaded with heavy instruments, cameras and sensors. No existing launch vehicle could have sent the 13,000-pound craft directly to Saturn.

The gravity-assist process works by taking advantage of the gravitational pull between a moving planet and a spacecraft. The two objects tug on each other, creating an exchange of energy and giving the spacecraft a boost. Cassini has already looped around the sun twice, using Venus as a launch pad both in 1998 and on June 24, 1999. The orbiter used the opportunity to snap some photos as it passed.