Rocky
Alien anatomy, base 6, and chord-based communication
Spoiler warning: this page discusses the novel's plot up to this chapter. It doesn't quote passages from the book.
Grace sees Rocky for the first time: pentagonal symmetry, five limbs, rock-like shell, no visible eyes. Rocky breathes ammonia at 29 atmospheres, speaks in musical chords, and counts in base 6. Two species that couldn't be more different begin to understand each other.
Eridian anatomy: pentagonal symmetry
Rocky has pentagonal symmetry, five prehensile limbs, ~45 cm shell, rock-like skin, no visible face or eyes.
The science behind it
Pentagonal symmetry is rare on Earth: only echinoderms (sea urchins, starfish) have it. Most animals have bilateral symmetry (two symmetric sides).
In zero gravity, radial symmetry has advantages: there's no "up" or "down," so being able to grab in any direction is useful. Five prehensile limbs allow movement in any orientation.
Rocky has no eyes Grace can recognize. This doesn't mean he can't perceive his environment: he uses a completely different sense (sonar), revealed in the next chapter.
His rock-like skin is a protective shell, like arthropod armor (insects, crustaceans). Consistent with a high-pressure, high-temperature environment.
Key terms
Communication with proton models
Rocky delivers spheres with xenonite molecules: one with O₂ (8+8 protons) and another with 29 NH₃ molecules. Message: your 1 atm O₂ vs my 29 atm NH₃.
The science behind it
The number of protons defines the element: 1 = hydrogen, 8 = oxygen, 7 = nitrogen. It's universal: any species with nuclear physics knowledge would understand.
29 atmospheres of NH₃ equals ~2,900 kPa, like being 280 meters underwater. Would kill a human instantly.
Xenonite withstands 29 atm in a flat panel—the worst geometry for containing pressure. A sphere distributes force evenly; a flat panel concentrates stress at edges. The material compensates with extraordinary strength.
Key terms
Rocky's language: musical chords
Rocky "speaks" by emitting chords (multiple simultaneous notes). Grace realizes it's a sophisticated language with phonemes based on frequency combinations.
The science behind it
Rocky produces sound without a visible mouth, likely through shell vibration or specialized membranes. Crickets and cicadas produce sound through friction; it's biologically plausible.
A linguistic system based on chords (simultaneous frequencies) has more information density than sequential human languages. We say one letter at a time; Rocky says a complete chord at once.
Useful sound frequencies are limited by physics: very low waves need large organs; very high waves attenuate quickly. Both species hearing in similar ranges isn't coincidence: it's a consequence of acoustic laws.
Key terms
Base 6 number system: anatomy determines mathematics
Rocky shows a clock with 5 rotors of 6 symbols each. Grace discovers they use base 6 (3 fingers × 2 counting hands).
The science behind it
Humans use base 10 because we have 10 fingers. Eridians use base 6 because they have 3 fingers on each of their 2 "counting hands."
Computers use base 2 (binary: 0 and 1) and base 16 (hexadecimal: 0-9 and A-F). There's nothing mathematically special about 10: any base works equally well.
One Eridian second = 2.366 Earth seconds. Establishing a shared time unit is the first step for any scientific exchange: without it, you can't measure speeds, frequencies, or energies.
The clock as the first universal language: regardless of language, an odometer shows "number that increases over time." It's pure math, understandable without translation.
Key terms
Try it yourself
How to use the simulator
In base 10 each position is worth ten times the one to its right (ones, tens, hundreds). In base 6 each position is worth six times as much: ones, sixes, 36s, 216s... and only the digits 0 to 5 are used. The converter works both ways, so you can type in either box.
Controls
- Base 10 box: type a decimal number to see it in base 6.
- Base 6 box: type a number using only the digits 0 to 5.
- Example buttons: hand-picked numbers with interesting results.
Things to try
- Type 6, 36 and 216: you get 10, 100 and 1000, the powers of six.
- Try 346, Grace's pendulum count: in base 6 it's 1334.
- Try typing a 6 or a 7 in the base 6 box. They don't exist in that system, just as base 10 has no single digit for ten.
Loading simulator…
Open “Base 10 to base 6 converter” on its own page, with an explanation and a worked example →
Worked example: the force on a flat panel
Between Rocky's side (29 atm) and Grace's (1 atm) there's a 28-atmosphere difference, about 2.84 million pascals. The force on a wall is pressure times area, so a 1 m² panel carries 2.84 million newtons: the weight of about 290 tonnes, like resting two blue whales on a window.
Shape matters a great deal. In a sphere of radius r and wall thickness t, the stress is σ = P·r / (2t), half that of a cylinder the same size. A flat panel, though, gets bent by the pressure, and the stress at its edges grows with the square of its width divided by the square of its thickness. That's why submarines and scuba tanks are round, and why a flat panel at 29 atm is proof of just how strong xenonite is.