#8 Malena Rice - Planet Nine, Oumuamua, Misaligned Exoplanets

Episode Overview

• This episode features an interview with Dr. Malena Rice, a professor at Yale University, whose research program uniquely connects the search for Planet Nine, the study of interstellar objects, and the analysis of exoplanets.
• The discussion contrasts the first two interstellar visitors, the mysterious 'Oumuamua and the more familiar comet 2I/Borisov, exploring what their detection implies about the total population of such objects.
• A central topic is the architecture of distant solar systems, focusing on spin-orbit misalignment—the angle between a star's rotation and its planets' orbits—as a clue to their formation history.
• The conversation explains the Rossiter-McLaughlin effect, a key observational technique used to measure spin-orbit misalignment, and highlights the importance of studying "pristine" resonant planetary systems.

Key Concepts

• Unified Research Program: Dr. Rice's work integrates three distinct fields—the search for Planet Nine in our solar system, the study of interstellar objects like 'Oumuamua, and the analysis of exoplanet system architecture—into a single cohesive research area.
• Interstellar Objects: The first two detected interstellar objects, 'Oumuamua and 2I/Borisov, showed very different characteristics. The surprising frequency of their detection suggests a higher-than-expected population of such bodies, with "dark" objects potentially being far more numerous than bright comets.
• Spin-Orbit Misalignment: This is the angle between a star's rotational axis and the orbital plane of its planets. The degree of misalignment can indicate whether a system formed peacefully from an aligned disk or experienced chaotic dynamical events like planet-planet scattering.
• Rossiter–McLaughlin Effect: An observational technique that measures the Doppler shift of a star's light as a planet transits across its face. The pattern of the shift reveals the planet's orbital direction relative to the star's spin, allowing astronomers to calculate the spin-orbit misalignment.
• Resonant Planetary Systems: Systems where planets are in a stable orbital resonance are considered dynamically "pristine." They likely haven't undergone major gravitational disruptions, making them ideal laboratories for studying the primordial configuration of planetary systems.

Quotes

• At 0:13 - "...the mentorship of the legendary Greg Laughlin, one of the most innovative scientists I know in the field of astronomy, and it obviously rubbed off on her..." - Kipping praises both Dr. Rice and her influential PhD mentor.
• At 26:24 - "[The media] just did not care about Borisov." - The speaker contrasts the massive media speculation about 'Oumuamua with the lack of interest in the more comet-like interstellar object Borisov.
• At 28:30 - "You'd have to have far more of the dark things than the cometary things to end up with a one-to-one ratio of them." - The speaker explains the detection bias, noting that since comets (like Borisov) are brighter, finding one comet for every one dark object (like 'Oumuamua) implies the dark objects must be far more numerous in reality.
• At 47:43 - "You would get that classic sort of symmetric curve... but if it is going backwards, then you'd get the blue shift and then the red shift, so it'd be just flipped the other way." - The guest explains how the Rossiter-McLaughlin effect's signature in radial velocity data reveals whether a planet's orbit is aligned (prograde), misaligned, or even backward (retrograde).
• At 56:01 - "[Resonant systems] are probably some of the most, quote unquote, pristine planetary systems... they retained that primordial configuration." - The guest explains why planetary systems in orbital resonance are valuable for study, as they likely haven't experienced major dynamical disruptions and can thus reveal the system's original alignment.

Takeaways

• The population of interstellar objects passing through our solar system is likely much larger than we can currently detect, and may be dominated by dark, non-cometary bodies.
• The alignment between a star's spin and its planets' orbits is a powerful diagnostic tool for understanding how a planetary system formed and evolved.
• Significant misalignments suggest a history of violent gravitational interactions, while well-aligned systems likely had a more tranquil past.
• Studying dynamically "pristine" systems, like those in orbital resonance, provides a clean window into the initial conditions of planet formation.