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-heliopause

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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-nasa

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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-exploration

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