RT @NASAScienceCast: Comet Siding Spring is about to fly historically close to Mars, and @MAVEN2Mars will have a ringside seat go.nasa.gov/1pb8L7O
RT @NASAScienceCast: Comet Siding Spring is about to fly historically close to Mars, and @MAVEN2Mars will have a ringside seat go.nasa.gov/1pb8L7O