StarTalk Radio: Cosmic Queries – Space Volcanoes: Fire and Ice with Natalie Starkey

Host: Neil deGrasse Tyson
Co-Host: Matt Kirshen
Guest: Dr. Natalie Starkey (Geologist and Science Communicator)
Date: December 23, 2025

Episode Overview

This Cosmic Queries edition of StarTalk explores the fascinating world of volcanoes in our solar system—both the fiery and the icy. Astrophysicist Neil deGrasse Tyson, comedian and science podcaster Matt Kirshen, and volcanologist-turned-space-rock-expert Dr. Natalie Starkey answer listener questions spanning everything from how volcanoes work on Earth and elsewhere, to bizarre, explosive scenarios both real and speculative. With humor and clarity, they reveal why volcanoes are far more diverse and widespread than most people imagine—and why our understanding of them shapes how we think about planetary evolution, habitability, and even the search for life.

Key Discussion Points and Insights

1. Introducing Dr. Natalie Starkey and ‘Fire and Ice’

• Background: Dr. Starkey is a geologist, science communicator, author of the book Fire and Ice, and public engagement officer at the UK’s Open University. She also wrote Hayden Planetarium’s show, Worlds Beyond Earth (7:22).
• Motivation: Inspired to study volcanoes by the book Surviving Galeras; became interested in both Earth and space volcanoes after studying comet and asteroid samples.
• Quote:
  “[After geology] I discovered actually you could do the same chemistry on rocks from space... I’m going to combine this all and write about volcanoes and space.” – Natalie Starkey (6:39)

2. Fire and Ice—What Do They Mean for Volcanoes?

• Fire:
  • “Fire” represents the classic, molten-rock volcanoes found on Earth, Venus, Mars, and Io (Jupiter’s moon).
  • Venus likely still has active volcanoes, but its thick CO₂ atmosphere makes direct observation challenging (10:36).
• Ice:
  • Most volcanoes beyond the asteroid belt (e.g., on moons of Jupiter and Saturn) are actually ice volcanoes (cryovolcanoes) spewing water and other volatiles due to internal heating—“cryovolcanism.”
  • “Most of the volcanoes out in the solar system, particularly when we go past the asteroid belt… are actually ice volcanoes.” – Natalie Starkey (8:39)

3. What Is a Volcano, Anyway?

• Definition Expanded:
  • A volcano is broadly any geological feature where internal material (solid, liquid, or gas) is expelled to a body’s surface (22:49).
  • Not all volcanoes are cone-shaped mountains—the archetype is Earth-centric; in space, volcanoes come in many forms.

4. How Do Ice Volcanoes Work? (Enceladus, Europa, etc.)

• Mechanism:
  • Tidal forces created by gravitational interactions (e.g., Saturn and its moons) generate internal friction and heat, melting ice and creating subsurface oceans (22:49).
  • Plumes of salty water, gases, and ice crystals escape through surface cracks—sometimes as high as 200 km, contributing to Saturn’s E ring (25:15).
• Biological Implications:
  • Material from deep oceans could (theoretically) carry life, shooting it into space through plumes.
  • “Anything could... come out in these plumes... We know that there’s chemical reactions happening within that ocean that can create organic molecules.” – Natalie Starkey (26:30)
  • Cassini mission sampled these plumes and detected salty, organic-rich material (25:15).

5. Volcanoes and Planetary Habitability

• Earth, Venus, and large moons remain geologically active due to internal heat from:
  • Formation energy (accretion/collisions).
  • Ongoing nuclear (radioactive) decay (45:20).
• Earth's dynamism: Volcanism helps maintain planetary temperature balance, but also underpins critical phenomena like the magnetosphere (48:10).
• “Volcanoes are basically just a manifestation of a planet cooling itself down.” – Natalie Starkey (45:20)

6. Notable Earth Volcanoes and Risks

• Supervolcanoes:
  • Yellowstone is often cited as “due” an eruption; risk is real but media hype is exaggerated (32:43).
  • Caldera eruptions can be massive, but ongoing monitoring offers early warning.
• Active Types:
  • Stratovolcanoes: Build up over thousands of years, can create beautiful but dangerous mountains (Fuji, Vesuvius).
  • Quote: “We forget as humans… volcanoes can erupt, not very often, but they’re still classed as active.” – Natalie Starkey (30:45)

7. Mars, Olympus Mons, and Giant Volcanoes

• Olympus Mons:
  • Tallest volcano and mountain in the solar system—almost three times the height of Everest (35:27).
  • Mars’s lower gravity and lack of plate tectonics allow volcanoes to grow much larger; on Earth, such structures would collapse under their own weight (36:43).
• Plate Tectonics:
  • Distinguishes Earth’s volcanic activity: chains like Hawaii form over stationary “hot spots” as plates drift (38:07).
  • Mars is a “stagnant lid” planet, so heat and volcanism can stay focused in one spot for eons (43:48).

8. Listener Cosmic Queries (Q&A Highlights)

a. Can normal mountains become volcanoes? (56:09)

• No. Traditional mountains (e.g., Himalayas) are built by plate collisions, not volcanism; they cannot “turn into” volcanoes.

b. Could humans tap or delay an eruption? (59:48)

• Generally, no. We lack predictive skill and ability to safely “vent” magma. Nature is best left alone; moving people is safer.
• “We just still don’t know enough about volcanoes to be able to predict their behavior.” – Natalie Starkey (59:48)

c. Can eruptions send debris to space? (52:13)

• On Earth, eruptions don’t achieve escape velocity due to gravity and atmosphere, but on small moons (e.g. Enceladus), eruptions easily eject material into space (53:03).

d. Can asteroids have volcanoes? (49:49)

• Yes! Dwarf planet Ceres shows evidence of cryovolcanism. Smaller asteroids/comets can expel material as they heat up near the Sun, affecting their orbits (50:01).

e. Can there be an "all-volcano" planet? (61:02)

• Io (Jupiter’s moon) is the closest example—rife with volcanic activity, reminiscent of early Earth.

Memorable Moments & Notable Quotes

• On recontextualizing volcanoes:
  “We have to just define better what a volcano is. We’re sort of skewed towards what we have on Earth... But we go out into the solar system and... start going, okay, well this is a volcano.” – Natalie Starkey (22:49)
• On volcanoes elsewhere:
  “On Io you’re almost certainly going to be captured by an eruption somewhere... even if not, you’ll probably have lava spattered on you.” – Natalie Starkey (35:06)
• On planetary cooling:
  “The volcanoes are basically just a manifestation of a planet cooling itself down.” – Natalie Starkey (45:20)
• On volcanic soil’s fertility:
  “That’s the thing about ash—it’s really, really good for soil. Small scatterings of ash quite often are really great for soil... acts as a fertilizer.” – Natalie Starkey (32:04)
• On volcanoes in sci-fi and culture:
  “My biggest takeaway from your answer there is that the Batman Robin film was scientifically accurate.” – Matt Kirshen, joking about Mr. Freeze and ice volcanoes (26:54)

Timestamps for Important Segments

• 03:39: Dr. Natalie Starkey’s background
• 06:09: “Fire & Ice” book inspiration, transition to space rocks
• 08:39: Introduction to ice volcanoes / cryovolcanoes
• 10:07: Active volcanism on Mars, Venus, Io
• 13:02: Jupiter’s moons and prevalence of cryovolcanism
• 15:00: Defining “cryovolcano” and their abundance
• 22:36: How ice volcanoes (e.g., Enceladus) erupt and create plumes
• 25:15: Cassini’s sampling of Enceladus’s plumes
• 27:21: The process of magma rising and eruptions (answered for young listeners)
• 32:30: Supervolcanoes—how dangerous are they, really?
• 35:27: Most menacing volcanoes and Olympus Mons
• 36:43: Gravity, planet size, and volcano growth
• 38:07: Plate tectonics, mantle plumes, and volcanic chains
• 43:48: Mars, “stagnant lid” planets, and fixed hot spots
• 45:20: Volcanoes and planetary cooling—sources of heat
• 48:10: Magnetic fields, planetary interiors, and habitability
• 50:01: Volcanism on asteroids/comets and orbital unpredictability
• 52:13: Could volcanoes launch material into space?
• 56:09: Can mountains turn into volcanoes? (Short answer: No.)
• 59:48: Could we tap or “defuse” a volcanic eruption? (Generally: No.)
• 61:02: Is a volcano-covered planet possible? (Io is the best example.)

Tone & Style

The episode is highly engaging, combining deep science with playful banter and cultural references. Dr. Starkey’s accessible yet detailed explanations are balanced by Tyson and Kirshen’s lighthearted humor—keeping the energy high and the science approachable.

For Further Exploration

• Natalie Starkey: @StarkeyStardust (social media)
• Matt Kirshen: @mattkirshen, Podcast: Probably Science
• StarTalk: Full catalog available on all major podcast platforms

Keep Looking Up!

Closing words from Neil deGrasse Tyson:
“As always for StarTalk, I bid you to keep looking up.” (62:57)