As it glanced around the Saturn system one final time, NASA's Cassini spacecraft captured this view of the planet's giant moon Titan. These views were obtained by Cassini on Sept. They are among the last images Cassini sent back to Earth.
Scientists determine a planet's ingredients in several ways, depending partly on how close it is to Earth. For planets like Mars that robots have visited, we analyzed rock and atmospheric samples on the spot. We also measure the planet's magnetic.