Mindscape 264 | Sabine Stanley on What's Inside Planets

The host, Sean Carroll, introduces the podcast and shares his early fascination with science, particularly theoretical physics. He reminisces about his family's misunderstanding of his interest, which led to gifts related to astronomy rather than the physics he was drawn to. Despite his focus on astronomy during his undergraduate and graduate studies, he emphasizes his primary interest in fundamental physics. Carroll acknowledges his limited knowledge of current astronomical discoveries compared to experts in the field.

The discussion shifts to the evolution of our understanding of planets, highlighting the initial belief in a simple categorization of terrestrial planets and gas giants. The guest, Sabina Stanlee, an astronomer at Johns Hopkins, notes the expansion of this categorization with the discovery of exoplanets and the need to rethink planet formation theories. The conversation touches on the surprising discoveries of exoplanets in unexpected orbits, challenging early theories, and the importance of planetary migration in understanding these new findings.

The focus turns to the study of planetary interiors, starting with Earth. The limitations of direct exploration are discussed, as the deepest human-made drill only reaches a fraction of Earth's radius. The conversation emphasizes the use of indirect methods like seismology to study the interior. The importance of seismic waves in understanding Earth's structure, including the iron core and mantle, is highlighted. The discussion also touches on the challenges of digging deeper due to increasing heat and pressure.

The conversation continues with a discussion on the confidence level in our understanding of Earth's interior structure, underlining the wealth of data obtained from seismic activity. The use of modern analysis techniques and computational methods to create detailed 3D images of Earth's interior is emphasized. The discussion also corrects common misconceptions about the mantle, highlighting the complexity and variety of Earth's interior structure.

The discussion explores the reasons behind Earth's ongoing geological activity, despite its age. The conversation explains that all planets start out hot and the motions and processes we observe are a result of cooling. The role of radioactive elements like uranium and thorium in maintaining Earth's internal heat is discussed. The conversation also touches on how we estimate the amount of these elements in Earth's mantle and core.

The conversation focuses on the use of seismology in understanding Earth's interior and the advancements in seismic sensing technology. The deployment of sensors around the Earth and the inclusion of seismometers in space missions to the Moon and Mars are highlighted. The discussion also touches on the potential of using seismic data from the Moon to learn more about Earth's interior and the challenges associated with studying Venus's interior due to its lack of a magnetic field and extreme surface conditions.

The discussion delves into the challenges of studying Venus's interior, noting the absence of a magnetic field and the planet's slow rotation, which complicates the use of shape-based analysis. The conversation explores recent advancements in understanding Venus's interior through measurements of its rotation and procession rate. The lack of plate tectonics on Venus and its implications for the planet's core convection and magnetic field are also discussed.

The conversation explores the diversity among the four innermost planets in our solar system, emphasizing the unique circumstances that led to their distinct characteristics. The discussion highlights the impact of a giant impactor on Mercury's size and composition, the runaway greenhouse effect on Venus, and the influence of Jupiter on Mars's size. The conversation underscores the importance of specific details and probabilistic events in planetary formation and habitability.

The discussion focuses on the relationship between Earth and its moon, noting the moon's significance in understanding Earth's early history. The conversation explores the moon's formation from a giant impact and the similarities between the materials of Earth and the moon. The potential of studying the moon to learn about the early solar system and the impact theory is highlighted, as well as the challenges and prospects of future missions to the moon.

The conversation shifts to the gas giants, Jupiter and Saturn, discussing the surprising findings from the Juno mission about Jupiter's 'fuzzy core.' The discussion explores the concept of metallic hydrogen, which exists deep within Jupiter and is responsible for its strong magnetic field. The conversation also touches on the differences between Jupiter and Saturn, noting the unique storms at Saturn's poles and the insights gained from the rings about Saturn's interior.

The discussion moves to the ice giants, Uranus and Neptune, highlighting their distinct composition and magnetic fields. The conversation delves into the potential presence of superionic water and the possibility of diamond seas within these planets. The unique multi-polar magnetic fields of Uranus and Neptune are discussed, along with the challenges of understanding their interiors due to the high pressure and temperature conditions.

The conversation concludes with a discussion on the importance of small bodies in the solar system, such as dwarf planets, asteroids, and comets, as remnants of planet formation. The potential contributions of comets to the atmospheres of inner planets are explored. The discussion also touches on the prospects of finding life in our solar system, with a focus on the moon Titan and the possibility of life on Neptune's diamond ocean.