Starts With A Bang #128 - Planet formation and proto-protoplanets
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This episode of Starts With A Bang explores the fascinating process of planet formation, focusing on protoplanetary disks and the early stages of planetary system development. Dr. Charles Law, a NASA Sagan Fellow at the University of Virginia, joins host Ethan Siegel to discuss how planets form from dust and gas in the disks surrounding young stars. The conversation covers the critical timescale of planet formation—within just a few million years before the disk dissipates—and the role of dust in initiating planet formation through coagulation. Key observational breakthroughs from ALMA and the James Webb Space Telescope are highlighted, particularly the discovery of the massive, edge-on protoplanetary disk known as Gomez's Hamburger (Go-Ham B), where a potential proto-protoplanet has been identified through localized emission of sulfur monoxide, indicating heating from a forming object. The episode also examines the two main planet formation theories—core accretion and disk instability—and how new observations are reshaping our understanding of planetary system diversity and evolution. The hosts reflect on how we're living in a golden age of astronomy, where cutting-edge tools allow us to witness planet formation in real time. The episode concludes with a forward-looking perspective on the future of planetary science. The discovery of Go-Ham B is presented not as a final answer, but as a catalyst for new questions about the survival, growth, and distribution of proto-protoplanets. The importance of multi-wavelength observations—combining ALMA’s millimeter data with JWST’s infrared capabilities—is emphasized to reveal the full structure of protoplanetary disks, from cold gas to warm dust. Dr. Law stresses that while we’ve made incredible progress, the real frontier lies in understanding the full diversity of planetary formation pathways. The episode ends on an optimistic note, celebrating the convergence of advanced instruments, models, and observational data that are transforming our ability to answer age-old questions about our cosmic origins and the prevalence of planets beyond our solar system.
Planet formation must occur within a narrow window of 1–10 million years before protoplanetary disks dissipate due to stellar radiation and winds.
Dust grains are essential for planet formation, as they coagulate to form rocky cores, while gas alone cannot efficiently clump together.
ALMA and JWST are revolutionizing our understanding by revealing disk structures, gaps, and localized heating signatures like sulfur monoxide emission in systems like Gomez's Hamburger.
The discovery of a proto-protoplanet in an edge-on disk challenges assumptions that such features are only visible in face-on systems.
The existence of massive, extended disks like Go-Ham B suggests that disk instability and rapid gravitational collapse may be more common than previously thought.
…and 3 more takeaways available in PodZeus
The Cosmic Stage: Stars, Disks, and the Birth of Planets
The episode opens with a vivid description of the universe's luminous structures, from stars to planets, and introduces the central theme: how planets form in protoplanetary disks around young stars. Host Ethan Siegel sets the stage by contrasting the early days of exoplanet discovery with today's rich catalog of over 6,000 known exoplanets, highlighting the rapid evolution of the field.
From Gas Clouds to Planetary Systems: The Core Accretion Model
Dr. Charles Law explains the standard model of planet formation, starting with giant molecular clouds collapsing under gravity to form protostars. The process of angular momentum conservation leads to the formation of thin, rotating protoplanetary disks. Dust grains coagulate in the disk midplane, forming the foundation for rocky cores and eventually planets.
The Critical Role of Dust and the Race Against Time
The episode emphasizes that dust—not just gas—is essential for planet formation. Dust particles settle to the disk midplane and collide to grow larger, a process that must happen quickly. The host and guest discuss the 'ticking clock' problem: planet formation must occur within a few million years before stellar radiation evaporates the disk.
ALMA's Revolution: Seeing Gaps and Rings in Protoplanetary Disks
The advent of ALMA has allowed astronomers to observe protoplanetary disks in unprecedented detail. The episode highlights the groundbreaking image of HL Tau, showing concentric rings and gaps that suggest the presence of forming planets. The analogy to Saturn’s rings is drawn, where moons sculpt gaps, suggesting similar processes in young systems.
The Transition Zone: When Do Planets First Appear?
Research suggests a transition phase: disks younger than half a million years appear uniform, while those older than two million years almost always show gaps. This implies planet formation begins around 1–2 million years after star birth. However, the exact timing remains debated due to observational challenges with younger systems.
“The discoveries we make now really don't solve everything. They just open up new interesting avenues where we can ask more precise and interesting questions for the future.”
“We only saw emission from this molecule most strongly in the region where we suspected this protoplanet candidate to be located.”
“This is a system where you would perhaps expect some of that gravitational collapse, direct collapse, that would maybe form a planet quite quickly.”
Host
Guest
ALMA
other
Gomez's Hamburger
other
James Webb Space Telescope
other
Ethan Siegel
person
Solar System
other
Go-Ham B
other
Charles Law
person
Carbon Monoxide
other
HL Tau
other
Sulfur Monoxide
other
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