Erid
An alien planet, steam-powered muscles, and nukes to save Earth
Spoiler warning: this page discusses the novel's plot up to this chapter. It doesn't quote passages from the book.
Grace reconstructs Erid's biology: a super-Earth with 25× stronger magnetic field, where Eridians run on biological steam engines and mercury blood. On Earth, a desperate plan: detonate nuclear bombs under Antarctica to release methane.
Planet Erid: a super-Earth without radiation
Erid has 8.5× Earth's mass, double the diameter, 5.1-hour days, and a 25× stronger magnetic field.
The science behind it
Earth's geomagnetic field is generated by the rotating molten iron core (dynamo effect). Erid: larger core + closer to its star + spins almost 5× faster (a 5.1-hour day against 24 hours) = 25× stronger field.
Erid's magnetopause (magnetic field boundary) is much farther than Earth's. Eridian ships orbited WITHIN the magnetic protection. They never needed radiation shielding.
With xenonite (extraordinary tensile strength), Eridians built a space elevator: a cable from the equator to geostationary orbit. Earth can't do this because no known material is strong enough.
Without radiation in their world, Eridian DNA has no damage repair mechanisms. Human DNA DOES (because we're constantly exposed to solar UV radiation). Eridians simply die when exposed.
Key terms
Eridian physiology: biological steam engines
Eridians have mercury blood, metal bones, muscles that work by vapor pressure, and two circulatory systems at 210°C and 305°C.
The science behind it
Eridian muscles are literally steam piston engines: receptacles with water at 210°C (under pressure, still liquid). Hot blood at 305°C heats the muscle → water expands as steam → contraction. Ambient blood (210°C) cools → relaxation.
Mercury is liquid from -39°C to 357°C, perfect for an organism operating between 210°C and 305°C. It's dense and conductive, ideal as a transport fluid.
Eridians produce their own oxygen (internal photosynthetic cells) and recycle CO₂. They're a walking closed biosphere. They only need food (energy) and heat dissipation.
Eridian sleep is "forced maintenance": the hot circulatory system (305°C) cools so specialized cells can repair the ducts. During this time, all muscles are paralyzed. Rocky can't wake up while sleeping.
Key terms
Nuclear bombs in Antarctica: methane to buy time
Dr. Leclerc orders detonation of 241 fusion bombs under Antarctica. Released methane will act as temporary greenhouse effect.
The science behind it
Fusion bombs (thermonuclear) use a fission explosion (uranium) to trigger fusion (hydrogen → helium). They produce less radioactive waste per unit of energy than a pure fission bomb, but they aren't clean: the fission stage and the neutrons that activate their surroundings still create fallout.
Methane (CH₄) is ~80× more potent as a greenhouse gas than CO₂ in the first 20 years. But it naturally decomposes to CO₂ + H₂O in ~10 years, making it "reversible."
Under Antarctic ice are fossil jungle remains from when Antarctica was tropical (millions of years ago). Methane (swamp gas) was trapped under the ice.
Without this intervention: 3.5 billion dead in 19 years from famine. With methane: the window extends to ~27 years. Extra time for the Hail Mary to find a solution.
Key terms
Try it yourself
How to use the simulator
Not all greenhouse gases warm the planet equally. The global warming potential (GWP) compares how much heat a ton of a gas traps with a ton of CO₂ over a set period, usually 20 or 100 years. The comparator shows the figures for four reference gases, based on the values published by the IPCC.
Controls
- The bars show each gas's 20-year GWP, relative to CO₂ (which is 1 by definition).
Things to try
- Compare methane over 20 years (about 80 times CO₂) with its 100-year value (about 28). The number falls because methane leaves the atmosphere in roughly a decade.
- Look at SF₆: it's thousands of times stronger than CO₂, but it's emitted in such small amounts that its overall effect is smaller.
- Consider why the novel picks methane and not SF₆: to warm quickly and be able to undo it later, you want a potent gas that doesn't linger for centuries.
Loading simulator…
Worked example: Erid's gravity and its space elevator
Surface gravity is proportional to a planet's mass and inversely proportional to the square of its radius. Erid has 8.5 times Earth's mass and twice its radius, so its gravity is 8.5 / 2² ≈ 2.1 times Earth's: about 21 m/s². Its average density is 8.5 / 2³ ≈ 1.06 times Earth's.
Escape velocity grows with √(M/R): √(8.5/2) ≈ 2.06. Where Earth needs 11.2 km/s to escape, Erid needs about 23 km/s. Through the rocket equation that multiplies the fuel you'd need enormously, which is why a space elevator looks so appealing there.
Geostationary orbit, where the elevator cable ends, lies at a distance from the centre proportional to (M·T²)^(1/3), with T the rotation period. For Earth it's 42,164 km. For Erid, with 8.5 times the mass and a 5.1-hour day: (8.5 × (5.1/23.93)²)^(1/3) ≈ 0.73, or about 30,700 km from the centre. Subtract Erid's radius (about 12,700 km) and the cable would be some 18,000 km long, half the length on Earth, though it would have to bear twice the gravity at its base.
Planets like this exist. 55 Cancri e, for instance, has about 8 Earth masses and 1.9 Earth radii. Astronomers call such worlds "super-Earths", and they are among the most common in the galaxy.