The New Horizons mission revealed Pluto's jaw-dropping vistas and geophysical mysteries. One listener wanted to know why the spacecraft didn't go into orbit around Pluto. Tom Spilker, interplanetary travel expert, tells us the answer.

In part 2, engineers who worked on the Galileo probe discuss what it was like when the probe entered Jupiter's atmosphere. This episode includes a bonus story about Pioneer Venus.

Celebrating the 20th anniversary of the successful deployment of a probe into Jupiter's atmosphere, this episode is a series of interviews with the engineers who worked on this challenging, historic mission.

Dr. George Privon talks about what galaxies are and what happens when two galaxies merge.

Dr. Dan Petrizzo explains what isotopes are, and what isotopes in water can tell scientists about ancient climates. He also explains how he made Mars rocks in the lab.

Professor Amy Lovell talks about listening in on radio waves coming from comets, as well as the particular challenges of using the world's biggest radio telescopes.

Professor Bethany Ehlmann discusses how to pick a landing site for NASA's next Mars rover, Mars 2020. Over a particularly good beer, we also cover looking for life on Mars, and she answers the thorny question: why look for life on Mars, which has little

Dr Bonnie Buratti talks about Pluto's big mystery: What is the source of energy that is causing all the active geology seen by New Horizons?

Dr. Jessica Watkins talks about enormous landslides on Mars that are millions of years old.

Dr. Michael Busch talks about the strange, low gravity surfaces of asteroids, and the challenges a visiting astronaut might face.