Are There Giant Caves on Mars?

Their discoverers call them the seven sisters. Are these holes in Mars merely very deep pits, or are they skylights opening on huge caves? Glen Cushing, Windy Jaeger, and Tim Titus of the United States Geological Survey will talk about these enigmatic features on the surface of the Red Planet. Emily Lakdawalla brings back a classic Q&A about how the Cassini team keeps track of a plethora of Saturnian rings and moons. Bruce Betts and Mat Kaplan present a special challenge to listeners in addition to our regular space trivia contest. Space headlines, too.