Voyager and the heliopause: Exploring where the Sun gives way to the stars

What does it really mean to enter interstellar space, and what have we learned since humanity first crossed the invisible boundary between our Sun and the stars? In this episode of Planetary Radio, we explore the science of the heliosphere and the realm beyond with Linda Spilker, project scientist for the Voyager mission at NASA Jet Propulsion Laboratory. Drawing on decades of experience with the twin spacecraft, Spilker shares how Voyager reshaped our view of the Solar System’s outer frontier, from the nature of the heliopause to the unexpectedly rich structure of the local interstellar medium. We unpack what Voyager 1 and Voyager 2 have taught us about charged particles, magnetic fields, and cosmic rays beyond the Sun’s protective bubble, and why those measurements have upended earlier ideas about where the Solar System truly ends. Spilker also reflects on the mission’s extraordinary longevity, the ingenuity required to keep the spacecraft communicating across the vastness of space, and what Voyager’s legacy means for future journeys between the stars. Then, in What’s Up, Bruce Betts, chief scientist at The Planetary Society, places Voyager in context, showing how long-lived missions shape the bigger picture of space science and why observing longer can lead to some of our most profound discoveries. Discover more at: https://www.planetary.org/planetary-radio/2026-voyagers-and-the-heliopauseSee omnystudio.com/listener for privacy information.

Marcia Smith, the founder and editor of Space Policy Online, joins the show and revisits a conversation we had one year ago, recorded just weeks before the second Trump administration took office. That episode, “The Challenges of Change at NASA,” explored the institutional and political roadblocks to radical change at the U.S. space agency. A lot has happened since that show, including DOGE, mass staff departures, a draconian budget cut proposal, a dramatic shift toward sending humans to Mars, and the rapid departure of 20% of NASA's workforce. But at the end of the year, much remains the same. The SLS and Orion programs continue unchanged, with funding locked in through 2032. The humans-to-Mars policy has effectively vanished; returning U.S. astronauts to the Moon, to stay, is again centered within civil space policy. NASA's science missions, though still facing a serious budgetary threat, have not gone away. So, did we see real change at NASA? And to what end? Or was it merely disruption masquerading as change? Marcia Smith and host Casey Dreier revisit their original analysis and discuss what they got wrong, what they got right, and what surprised them about 2025 in civil space policy. Discover more at: https://www.planetary.org/planetary-radio/spe-2025-a-year-of-disruption-and-change-at-nasaSee omnystudio.com/listener for privacy information.

As 2025 comes to a close, Planetary Radio looks back on a year that reshaped space exploration, through stunning discoveries, major milestones, unexpected challenges, and the people who carried science forward through it all. In this episode, Sarah Al-Ahmed, host and producer of Planetary Radio, is joined first by Kate Howells, public education specialist at The Planetary Society, to share results from The Planetary Society’s Best of 2025 campaign and the newly released 2025 Year in Pictures edition of The Planetary Report. They discuss the images, missions, and accomplishments voted on by the global space community, and how space imagery continues to inspire curiosity, connection, and hope. Then, Sarah sits down with Mat Kaplan, senior communications advisor, Asa Stahl, science editor, and Ambre Trujillo, digital community manager at The Planetary Society, for a wide-ranging conversation about the defining space exploration stories of 2025.  The episode closes with Bruce Betts, chief scientist of The Planetary Society, in What’s Up, where he looks ahead to what’s coming in 2026. Discover more at: https://www.planetary.org/planetary-radio/2025-looking-back-space-explorationSee omnystudio.com/listener for privacy information.

2025 was one of the most consequential years for space policy in modern U.S. history. In this special year-in-review episode, Planetary Radio takes a deep dive into what happened behind the scenes in U.S. space policy and advocacy as NASA faced unprecedented proposed cuts to its science programs. With nearly half of NASA’s science budget at risk, dozens of missions threatened, and months of leadership uncertainty at the agency, this year became a defining moment for the future of space science. Sarah Al-Ahmed is joined by Casey Dreier, chief of space policy at The Planetary Society, Jack Kiraly, director of government relations, and Ari Koeppel, an AAAS science & technology policy fellow, to unpack how this crisis unfolded and how scientists, space advocates, and lawmakers responded. Together, they explore how public advocacy helped shift the conversation in Congress. Plus, in What’s Up, Chief Scientist Bruce Betts explains why stability matters so much for space science and what’s at stake when long-term missions are disrupted. This is the first of two special year-end episodes. Next week, Planetary Radio will look back at what humanity accomplished in space exploration in 2025, from new missions and discoveries to milestones across our Solar System and beyond. Discover more at: https://www.planetary.org/planetary-radio/2025-looking-back-space-policy-and-advocacySee omnystudio.com/listener for privacy information.

It was such a delight to feature work by our own Kate Howells in The Planetary Society’s member book club. We keep Kate busy as our public education specialist, but she found time to write about many of her favorite natural satellites in this richly illustrated edition. Join her and book club host Mat Kaplan for a journey taking us from our own Moon, past Europa, Titan, and many more, and out across a galaxy that is no doubt full of worlds circling other worlds.  Discover more at: https://www.planetary.org/planetary-radio/book-club-kate-howellsSee omnystudio.com/listener for privacy information.

Thirty years ago, NASA’s Galileo spacecraft became the first mission to orbit Jupiter, opening a new chapter in our exploration of the outer Solar System. Over eight years around Jupiter, Galileo transformed how we understand Jupiter and its moons, revealing a powerful and dynamic planetary system, uncovering evidence for oceans hidden beneath icy worlds, and reshaping the search for life beyond Earth. To mark the 30th anniversary of Galileo’s orbital insertion, scientists, engineers, historians, and advocates gathered at the California Institute of Technology for a special symposium: Galileo at 30. In this episode of Planetary Radio, host Sarah Al-Ahmed takes you inside that celebration. You’ll hear how Galileo survived seemingly impossible challenges, how its team adapted when things went wrong, and how its discoveries reshaped planetary science. You’ll hear from key voices in Galileo’s story, including historian Erik Conway, project manager Bill O’Neil, magnetometer principal investigator Margaret Kivelson, Europa Clipper Project Scientist Bob Pappalardo, and Dragonfly mission Principal Investigator Elizabeth “Zibi” Turtle, along with reflections from many others whose lives and careers were shaped by this remarkable mission. Together, they tell the story of Galileo not just as a spacecraft, but as a shared human effort, one whose legacy continues to guide exploration today. Discover more at: https://www.planetary.org/planetary-radio/2025-galileo-at-30See omnystudio.com/listener for privacy information.

Why do we explore space, and why does science matter in the first place? In this Space Policy Edition rerun, Planetary Society Chief of Space Policy Casey Dreier revisits a deeply influential 2020 conversation with philosopher and ethicist J. S. Johnson-Schwartz, author of The Value of Science and Space Exploration. As debates over NASA’s budget and the future of space science continue to resurface, this conversation remains strikingly relevant. Dr. Johnson Schwartz makes a compelling philosophical case that science itself is not merely useful or beneficial, but a moral obligation. Beyond economic returns, technological spinoffs, or national prestige, the pursuit of knowledge has intrinsic value, and public space agencies play a critical role in representing that shared human interest. Discover more at: https://www.planetary.org/planetary-radio/the-moral-case-for-spaceSee omnystudio.com/listener for privacy information.

The 2025 International Mars Society Convention convened at the University of Southern California this October for three days of passionate discussion about humanity’s future on the red planet. Speakers explored science, policy, technology, AI, synthetic biology, and the long-term path toward becoming a multi-planet species. In this episode, Mat Kaplan, senior communications adviser at The Planetary Society, shares his conversations with speakers and guests at the Convention. We hear from Robert Zubrin, founder of The Mars Society, who delivered a fiery call to protect NASA’s science programs in the face of unprecedented budget cuts. Humphrey “Hoppy” Price, Chief Engineer for NASA’s Robotic Mars Exploration Program at the Jet Propulsion Laboratory, updates us on the future of Mars Sample Return and new mission architectures. Keynote speaker Dex Hunter-Torricke, a longtime communications leader for SpaceX, Meta, and other major tech organizations, reflects on AI’s promise and peril, and why Mars remains a beacon of hope for humanity’s future. Biologist and technologist Tiffany Vora, vice president for innovation partnerships at Explore Mars, and Erika DeBenedictis, biologist and founder of Pioneer Labs, reveal breakthroughs in synthetic biology and engineered microbes that could help future Martians survive. Steve Benner, chemist and founder of the Foundation for Applied Molecular Evolution (FfAME), revisits the Viking lander experiments and makes a provocative case that we may have found Martian life nearly 50 years ago. Architect Melodie Yashar, CEO of AENARA and a pioneer in 3D-printed habitat research, shares progress in additive construction on Earth and Mars. James Burk, executive director of The Mars Society, discusses advocacy, analog research stations, and the organization’s expanding international footprint. Finally, we meet Sasha, a 13-year-old presenter whose enthusiasm offers a bright glimpse of the next generation of explorers. We wrap up the show with What’s Up with Bruce Betts, chief scientist at The Planetary Society, with a discussion of perchlorates in the Martian soil. Discover more at: https://www.planetary.org/planetary-radio/2025-mars-society-conventionSee omnystudio.com/listener for privacy information.

NASA’s twin ESCAPADE spacecraft have finally launched on their journey to Mars. Designed to study how the solar wind interacts with Mars’ patchy magnetic fields and drives the loss of its atmosphere, ESCAPADE is NASA’s first dual-spacecraft mission to the Red Planet and a major milestone for the SIMPLEx program’s small, low-cost planetary explorers. The mission began its voyage aboard Blue Origin’s New Glenn rocket after several weather and space weather delays, marking the vehicle’s first science launch. We begin with Ari Koeppel, AAAS Science & Technology Policy Fellow and Space Policy Intern at The Planetary Society, who was at Cape Canaveral for the prelaunch activities. Ari shares what it was like to navigate repeated scrubs and even a powerful solar storm, along with the emotional experience of watching a spacecraft carrying an instrument he helped build begin its voyage to Mars. Next, we are joined by Dr. Rob Lillis, ESCAPADE’s Principal Investigator and Associate Director for Planetary Science at UC Berkeley’s Space Sciences Laboratory. Rob explains how ESCAPADE aims to unravel Mars’ complex space environment using two coordinated orbiters, why its measurements are key to understanding atmospheric escape, and how its innovative trajectory made the mission possible after the loss of its original rideshare opportunity. Finally, Dr. Bruce Betts, Chief Scientist of The Planetary Society, returns for What’s Up to talk about why Mars produces aurora even without a global magnetic dynamo. Discover more at: https://www.planetary.org/planetary-radio/2025-escapadeSee omnystudio.com/listener for privacy information.

This week on Planetary Radio, we’re sharing a special conversation from our friends at the Smart Girl Dumb Questions podcast. Host Nayeema Raza sits down with The Planetary Society’s Chief of Space Policy, Casey Dreier, to explore one of the most common questions in space exploration: Why does space matter, and is it really worth the cost? Casey breaks down how space exploration impacts daily life, from GPS and weather forecasting to cutting-edge technologies and scientific discoveries that could reshape our future. Together, Nayeema and Casey unpack the big ideas behind NASA’s ~$25 billion budget at a moment when U.S. national priorities are shifting. Stick around after the interview for a special U.S. Thanksgiving-week edition of What’s Up with Chief Scientist Bruce Betts. Discover more at: https://www.planetary.org/planetary-radio/2025-smart-girl-dumb-questionsSee omnystudio.com/listener for privacy information.