Andrew Denning talks about the Nazi cult of mobility, a set of ideas and practices that were crucial to its racist ideology. Denning is an Assistant Professor of Modern European History at the University of Kansas in Lawrence. He is the author the essay "'Life is Movement, Movement is life!' Mobility Politics and the Circulatory State in Nazi Germany," published in the American Historical Review.

Annette Joseph-Gabriel speaks to Jessica Nabongo about her quest to be the first black woman to travel to all of the countries of the world. Joseph-Gabriel is an Assistant Professor of French and Francophone Studies at the University of Michigan, Ann Arbor. Nabongo is a writer, entrepreneur, and the founder of Jet Black, a boutique luxury travel company that promotes tourism to Africa, the Caribbean, and Central and South America.

Journalist Carl Hoffman talks about Bruno Manser and Michael Palmieri, two men who arrived in Borneo with very different dreams and aspirations. Hoffman served as a contributing editor to National Geographic Traveler and Wired Magazine. He is the author of The Last Wild Men of Borneo: A True Story of Death and Treasure.

Dr. Beth Taylor talks about the physiological differences between men and women athletes and why ultra-endurance events seem to offer certain performance advantages to women. Taylor is an associate professor of kinesiology at the University of Connecticut and the Director of Exercise Physiology Research in Cardiology at Hartford Hospital.

Lucianne Walkowicz talks about the ethics of colonizing Mars and new developments in the search for extraterrestrial life. Walkowicz held the 2017 NASA Chair in Astrobiology at the Library of Congress. She is currently an astronomer at the Adler Planetarium.

Daniel Kennefick talks about resistance to relativity theory in the early twentieth century and the huge challenges that faced British astronomers who wanted to test the theory during the solar eclipse of 1919. Kennefick is an associate professor of physics at the University of Arkansas, Fayetteville. He's the author of No Shadow of Doubt: the 1919 Eclipse that Confirmed Einstein's Theory of Relativity.

Emily Kern talks about the search for human origins in the 19th and 20th centuries, specifically why anthropologists came to see Africa – rather than Asia – as the cradle of the human species. Kern is a Postdoctoral Research Associate in New Earth Histories at the University of New South Wales.

Director Robert Stone talks about his film Chasing the Moon, a three-part documentary which aired on PBS's American Experience for the fiftieth anniversary of the Apollo 11 mission.

Margaret Schotte talks about how sailors were trained to do the difficult and dangerous work of navigation in the early modern world. Schotte is an Assistant Professor of History at York University. She is the author of Sailing School: Navigating Science and Skill.

Ed Armston-Sheret talks about the mysterious disease of scurvy: how it affected expeditioners and why it was so difficult to understand. Armston-Sheret is a PhD candidate at Royal Holloway University of London. He's the author of "Tainted bodies : scurvy, bad food and the reputation of the British National Antarctic Expedition, 1901–1904," published this year in the Journal of Historical Geography.