The episode features Neil deGrasse Tyson hosting a Cosmic Queries edition on fire and ice with comedian Matt Kirshen and geologist-turned-space scientist Natalie Starkey. Starkey is Public Engagement Officer at the Open University, author of Fire and Ice, and writer of the current Hayden Planetarium space show Worlds Beyond Earth.

The discussion explores volcanic activity throughout the solar system, from Earth's familiar molten rock volcanoes to the ice volcanoes (cryovolcanoes) found on moons orbiting Jupiter, Saturn, and beyond. Starkey explains how most volcanoes in the solar system actually erupt ice and water rather than molten rock.

Topics covered include why Olympus Mons on Mars grew so large, whether Venus still has active volcanoes, how Yellowstone's supervolcano actually works, and why Iceland can generate all its electricity from geothermal energy. The conversation also addresses whether Earth's cooling core threatens our magnetic field and atmosphere.

Listener questions explore everything from ice volcanoes on Enceladus creating Saturn's rings to whether asteroids can develop volcanoes that alter their orbits, revealing the surprising prevalence and diversity of volcanic activity across our solar system.

Ice Volcanoes Dominate the Outer Solar System

Beyond the asteroid belt, most volcanoes are ice volcanoes (cryovolcanoes) rather than rocky ones. "Most of the bodies out there are actually ice volcanoes" erupting water, ammonia, methane, and nitrogen instead of molten rock - Natalie

Enceladus, a moon of Saturn, shoots plumes of ice particles, gases, and silica grains from its subsurface ocean so high that some particles escape to form Saturn's E-ring

"We know where they're coming from because they're salty. We know they're from a salty liquid ocean below the crust" - Natalie, explaining how Cassini mission sampling revealed Enceladus has all the right conditions for life

The definition of a volcano must expand beyond Earth's conical mountains: "Material coming out from the inside of this world and it's spewing out onto the surface" driven by internal heat - Natalie

Tidal heating powers these ice volcanoes as moons get squeezed closer and farther from their parent planets, creating friction and heat that melts subsurface ice into liquid oceans

Venus: Earth's Volcanic Twin Gone Wrong

Venus likely has active volcanoes erupting today but its thick carbon dioxide atmosphere makes direct observation impossible with visible light, requiring radar to penetrate

"The whole of Venus is about the same age. It looks like it's about 500 million years old" based on lava flow coverage, indicating recent geological activity - Natalie

Venus has surface temperatures of 450 degrees Celsius (hot enough to melt lead) and crushing atmospheric pressure, making it inhospitable despite being Earth's size and made of the same ingredients

NASA plans two missions to Venus in the next decade, ESA one mission, and India another, shifting focus from Mars exploration. "Venus is going to be the next planet we're really going to delve into" - Natalie

The key scientific question is why Venus ended up so different from Earth despite similar origins, particularly why it lacks surface oceans

Olympus Mons: Mars' Monster Volcano

Olympus Mons is three times higher than Mount Everest and couldn't exist on Earth because "it would basically collapse under its own weight because it would just be too heavy" due to Earth's stronger gravity - Natalie

Mars lacks plate tectonics, creating a "stagnant lid planet" where mantle plumes erupt through the same spot for potentially a billion years, allowing volcanoes to grow enormous

On Earth, the Hawaiian island chain forms as tectonic plates move over a stationary mantle plume, creating a linear sequence of volcanoes like a "factory line" - Matt's analogy

"If you go to Honolulu and people are like, oh, it's volcanic. Could it erupt? You're like, no, you can't because it's nowhere near that plume now" - Natalie, explaining why older Hawaiian islands are safe

Mars was massively volcanically active about 3 billion years ago and had conditions suitable for life, but its smaller size meant it cooled faster than Earth

Io: The Solar System's Volcanic Hotspot

"Io is the most volcanically active object in the solar system" with plumes erupting almost continuously - Natalie. Every space mission flyby has observed active eruptions

Io resembles Earth 4 billion years ago when volcanoes erupted constantly across the planet's surface, though Earth was never quite as extreme

Tidal heating from Jupiter's massive gravitational pull continuously squashes and squeezes Io, creating friction and heat that drives perpetual volcanic activity

"I wouldn't want to be sitting on Io because I think on Io, you're almost certainly going to be captured by an eruption somewhere" - Natalie, calling it the most menacing volcano in the solar system

Yellowstone and Supervolcano Threats

Yellowstone is frequently described as "due" to erupt, but "whilst they have the potential to do that...it doesn't mean it's all going to erupt in one go" - Natalie

Supervolcanoes create caldera eruptions where "the ground will literally just explode and you'll end up with this massive caldera left behind" rather than building a mountain

"If one is really going to erupt, then we're going to know about it because we're studying them in detail" through seismic surveys that detect hot spots and molten material - Natalie

Supervolcanoes often have small eruptions that "let off a bit of steam" preventing catastrophic eruptions, making them "almost never as bad as we think they're going to be"

Mount St. Helens exploded when magma containing pressurized gases reached the surface, "blowing that mountain apart as that pressure is released"

Earth's Cooling Core and Magnetic Field

Earth retains heat from two sources: primordial heat from collisions 4.5 billion years ago, and continuous nuclear heat from radioactive decay of unstable atoms in the mantle

"Volcanoes are basically just a manifestation of a planet cooling itself down. So it has all this internal heat and it needs to go somewhere" - Natalie

Earth's magnetic field depends on its molten iron outer core rotating around a solid inner core, shielding life from solar radiation that would otherwise strip the atmosphere

Mars lost its magnetic field when its core solidified due to faster cooling from its smaller size, making surface life impossible without underground protection from radiation

Terraforming Mars faces fundamental challenges because "you might be able to turn it into Earth, but to sustain it requires the rest of this shielding" - Neil

Iceland's Geothermal Energy Revolution

Iceland generates all its electricity from geothermal energy by pumping water into the crust where volcanic heat turns it to steam, providing essentially free power

Iceland sits on the mid-ocean ridge with a mantle plume underneath, making it "a massively volcanic place" with abundant accessible heat just below the surface - Natalie

"They send heat on their roads and it melts all the ice. So then they don't have to grit the roads" and can maintain outdoor heated swimming pools year-round - Natalie

Until the 1990s Iceland still used fossil fuels before fully transitioning to geothermal power, demonstrating how recently this technology was adopted

Volcanic ash is "really, really good for soil" because it absorbs water and acts as fertilizer, making volcanic regions agriculturally valuable despite eruption risks

Plate Tectonics: Earth's Unique Feature

Plate tectonics was only fully embraced by geologists in the 1960s, making it relatively recent scientific consensus despite earlier suggestions

"Earth was the only body that we know of that has this. I thought it was a fairly universal planet" - Neil, surprised to learn plate tectonics is unique to Earth

The Himalayas and Mount Everest are not volcanic but form from "two plates colliding" as the Indian subcontinent pushes into Asia, growing taller every year

"Normal mountains...never will be" volcanic because they form from tectonic compression rather than magma eruption - Natalie