To Pluto and Beyond with Alan Stern

Episode Summary

Executive Summary: This episode centers on Alan Stern’s update on New Horizons after Pluto and Arrokoth: the spacecraft remains healthy, is producing new science in the Kuiper Belt and heliosphere, and may yet visit another object. Stern also discusses the case for a future Pluto orbiter, New Horizons’ stellar parallax experiment, and how suborbital commercial flights could enable affordable science.

Main Topics: New Horizons at 5 years past Pluto: Stern reviews the mission’s status, noting the spacecraft remains in excellent health, with fuel and power for potentially decades more work as it continues outward through the Kuiper Belt. Pluto’s evolving science case: The conversation highlights post-flyby discoveries: Pluto may be an ocean world with cryovolcanism, a young nitrogen glacier, and possible resurfacing or transport of organics from the interior. Arrokoth and planetesimal formation: Stern explains how Arrokoth’s shape and geology support streaming instability/pebble-cloud collapse and challenge hierarchical accretion models for small body formation. Future Pluto orbiter concept: The episode explores why Pluto is a compelling target for an orbiter, including possible plume sampling, the technical challenges of orbit insertion and communications, and competition for flagship mission funding. New Horizons beyond the solar system: New Horizons continues heliosphere science, including pickup ions, dust, and hydrogen measurements, while also enabling unique stellar parallax imagery and onboard navigation experiments. Commercial suborbital science: Stern discusses scientific opportunities on Blue Origin and Virgin Galactic flights, emphasizing lower cost, rapid iteration, and use for astronomy, atmospheric studies, and microgravity experiments.

Key Arguments: New Horizons remains scientifically valuable long after Pluto because it is still healthy and operating in underexplored regions of the Kuiper Belt and heliosphere. Pluto’s geology is far more active and complex than expected, with evidence supporting an internal ocean, cryovolcanism, and geologically young nitrogen ice. Arrokoth’s contact-binary structure and flattened lobes strongly favor streaming instability as a planetesimal-formation mechanism. A Pluto orbiter would be transformative because it could study the far side of Pluto, search for plumes, and potentially fly through ejected material to sample it. Even though orbiting Pluto is difficult, the low gravity also helps extended exploration by making it easier to depart Pluto orbit for Kuiper Belt follow-on targets. Commercial suborbital vehicles can lower the cost of science by about an order of magnitude relative to sounding rockets and could support repeatable, rapid-turnaround research. New Horizons is already doing unique science from far away that Earth-based observatories cannot replicate, including parallax imaging of nearby stars and interstellar navigation tests.

Data Points: Time since New Horizons launch: 14.5 years in space - Stern describes the mission’s longevity since launch in early 2006. Pluto flyby anniversary: 5th anniversary - Episode recorded close to the fifth anniversary of the Pluto encounter on July 14, 2015. Distance from Sun: 47 times Earth-Sun distance - New Horizons’ current location at the time of the interview. Distance from Sun: more than 5 astronomical units beyond Arrokoth / over 2 billion miles past Pluto - Describes how far the spacecraft has traveled after Pluto and Arrokoth. Future milestone: 50 AU in early 2021 - Stern expects a celebration when New Horizons crosses 50 astronomical units. Potential remaining operational life: as much as 20 more years - Based on remaining fuel and power aboard the spacecraft. Pluto data return time: almost 18 months - Time needed to receive all data after the flyby. Observations made at Pluto: hundreds - Includes imagery, spectra, plasma measurements, and radio science on Pluto and its moons. Pluto moons observed: 5 moons - Stern notes New Horizons studied Pluto and its five moons. Pluto ocean hypothesis: liquid water ocean in its interior - Lines of evidence suggest Pluto may be an ocean world. Largest glacier cited: about the size of Texas and Oklahoma combined - Description of Pluto’s nitrogen glacier on the western side of Sputnik Planitia/Pluto’s heart. Glacier area: a million-plus square kilometers - Approximate size of the nitrogen glacier. New Horizons flyby coverage: about 40% of Pluto - The fast flyby mapped only part of Pluto at high resolution. Arrokoth discovery papers: 3 papers in Science (February) - Team published multiple papers on composition, geology, and origins. Suborbital cost advantage: about 10 times less than a sounding rocket - Stern says this makes commercial suborbital science attractive. Suborbital community meeting attendance: 300 or so researchers - Annual/biannual community meeting for suborbital science users. Stellar parallax targets: Proxima Centauri and Wolf 359 - New Horizons images combined with Earth-based images to create 3D views. Nearest star distance: about 7.9 light years - Wolf 359 is referenced as one of the closest stars in the experiment. Venus reflectivity: 77% - Bruce Betts cites Venus’ Bond albedo in the space segment. Earth reflectivity: about 31% - Comparison to Venus’ Bond albedo.

Pivotal Quotes: "I thought the solar system had saved the best for last." — Alan Stern: Stern reflects on Pluto’s surprising beauty and scientific richness after the flyby. "The curse of Pluto's low gravity that makes it hard to get into orbit turns out to actually be a two-sided coin." — Alan Stern: He explains why Pluto’s low gravity both complicates orbit insertion and aids future departure to other Kuiper Belt targets. "We really looked very hard and didn't find anything." — Alan Stern: On the search for geysers on Pluto, while noting that the flyby only covered part of the world.

Implications: New Horizons remains a pathfinder for Kuiper Belt science, Pluto follow-up, and heliosphere studies, while commercial suborbital platforms may soon open a cheaper, faster route for repeated space-based experiments and education.