Episode Summary
Executive Summary: Michael Shermer interviews Alan Stern and David Grinspan about their book and the New Horizons Pluto mission, emphasizing the long, uncertain path from idea to launch, the bureaucratic hurdles, and the scientific payoff. They argue Pluto remains a planet in planetary-science practice, explain why the mission was pursued, and describe how the flyby transformed Pluto from an oddball into a geologically active world with implications for planetary evolution, exploration, and humanity’s future in space.
Main Topics: Pluto’s status as a planet: The guests defend the scientific and practical use of 'planet' for Pluto, arguing the IAU definition was contrived, excludes exoplanets, and ignores intrinsic planetary properties. How New Horizons was conceived and funded: They trace the mission’s origin to late-1980s scientific interest, a successful feasibility study, and a decade-plus of persistence through NASA bureaucracy, budget pressures, and competition. Mission engineering, risk, and launch logistics: The conversation details spacecraft design tradeoffs, the need for RTGs, launch approvals across many agencies, launch delays, and the complexity of coordinating a low-mass, high-speed mission. The Jupiter flyby and cruise to Pluto: Jupiter served as both a gravity assist and a full systems test, while the long cruise required years of monitoring, planning, and keeping the spacecraft healthy before Pluto encounter. Pluto’s scientific surprises: New Horizons revealed Pluto as active and diverse, with glaciers, atmosphere, possible ocean, canyons, and resurfacing processes that challenge older assumptions about small icy bodies. What planetary exploration means for the future: The guests frame space exploration as a long human project, argue that the solar system is still wide open, and predict more missions, orbiters, and eventually human expansion beyond Earth.
Key Arguments: The IAU’s planet definition is scientifically weak because it was driven by classification convenience, not planetary properties; planetary scientists still routinely call Pluto a planet. Science should not be decided by vote; consensus should emerge from converging evidence across independent lines of inquiry. New Horizons succeeded because the team used a disciplined, low-cost design, accepted compromises, and focused on 'good enough' rather than overbuilding. Pluto was worth exploring because it was the last unvisited known world and turned out to be scientifically rich, including atmosphere, geology, and possible internal ocean. The mission demonstrates that careful study, persistent advocacy, and cross-disciplinary teamwork can make ambitious exploration possible even under tight constraints. Pluto’s post-flyby data show that small icy worlds can remain active far longer than previously believed, forcing a revision of planetary evolution models. Humanity is naturally exploratory and likely to expand through the solar system over time, aided by new commercial space capabilities.
Data Points: Years from project start to launch: 17 years - From the 1989 Pluto Underground effort to New Horizons launch in 2006 Launch window delay risk: Another decade - If the mission missed the Jupiter-assisted launch opportunity RTG efficiency: About 6% - Heat-to-electricity conversion in the nuclear power source RTG electrical output: About 200 watts - Power available to run spacecraft systems RTG heat output: About 5 kilowatts of heat - Thermal energy generated by the plutonium source Mission team size during operations: About 50 people - Core team after launch while spacecraft cruised to Pluto Total people involved over time: About 2,500 people - Design, build, launch, and support workforce for New Horizons Budget relative to Voyager: One-fifth the budget - New Horizons was built far cheaper than Voyager while accomplishing a Pluto flyby Jupiter distance from Sun: 500 million miles - Used to explain relative solar-system distances Pluto distance from Sun: More than 3 billion miles - Approximate distance discussed for context Spacecraft speed at launch: 30,000–32,000 miles an hour - Initial speed after launch, later increased by Jupiter assist Fastest launch claim: Still the fastest launch of a spacecraft ever from Earth - As described for New Horizons using Atlas V Jupiter gravity-assist timing to Pluto: 8 years - Cruise time from Jupiter flyby to Pluto encounter Pluto rotation period: 6.4 days - Relevant for imaging the whole body during flyby Closest-approach high-res data collection: 148 hours - Window during which all high-resolution data were collected Communication delay from Pluto: About 4.5 hours one way - Used to explain delayed problem-solving and data return Round-trip light-time delay: About 9 hours - Time for a command-response cycle between Earth and Pluto Planned scientific encounter duration: 6 months - January through July around closest approach Encounter observation span: 10 weeks on approach - Period when Pluto became better imaged than Earth-based observations Pluto atmosphere extent: A couple hundred miles - Altitude scale described for Pluto’s tenuous atmosphere Ground agencies approving launch: 42 state and federal agencies - Approval required for launching plutonium-powered spacecraft from Florida People behind mission readiness: 150 co-authors - Authorship count on the first Pluto results paper
Pivotal Quotes: "I call this, pardon my French, I call it BS, and that stands for bad science." — Alan Stern: Critique of the IAU planet-definition process and its schoolchild-memorization rationale "I'd rather have 80% of something than 100% of nothing." — Alan Stern: Explanation of the team’s engineering and mission-design philosophy "Pluto can't read textbooks." — Alan Stern: Summary of how New Horizons overturned assumptions about small, inactive worlds
Implications: The episode frames New Horizons as a model for disciplined exploration and scientific persistence. It suggests Pluto belongs in the active worlds category, supports broader planetary-science criteria, and points to a future of more ambitious robotic—and eventually human—expansion across the solar system.