Star map model

The star map model is a xenonite cylinder sent by the Eridian Rocky to communicate his origin and purpose to Ryland Grace. It is a three-dimensional map of local stars centered on Tau Ceti, with a filament connecting Tau Ceti to 40 Eridani, revealing that Rocky's species comes from the 40 Eridani system and is also threatened by Astrophage. This object is the first successful cross-species communication device, establishing that both parties share the same mission to understand why Tau Ceti is immune to Astrophage.

Design and Appearance

The star map model is a cylinder made of xenonite, the same mottled gray-and-tan material as the Blip-A's hull. It unscrews with a left-handed thread, which Grace initially fails to recognize, causing the two halves to refuse to mate until he reverses his motion. Inside the bottom half, a single whisker-thin pole supports a marble-sized sphere and a BB-sized sphere connected by a parabolic arc, which Grace immediately identifies as a Petrova line—the arc of infrared light that Astrophage use to migrate from a star to a planet. The top half contains dozens of whiskers, each ending in a sphere less than a millimeter across. Grace counts thirty-one whiskers, each with its own sphere, and notices one whisker in the exact center that holds a miniature replica of the Petrova-line model, about one-twentieth the scale of the main one. This miniature is connected by an even thinner whisker to another sphere on a different whisker, forming a nested structure.

Decoding the Message

Grace uses the ship's reference library to plot the positions of the spheres against known star data. He finds that the spheres correspond to local stars in their correct relative positions, with Tau Ceti at the center. The point of view is offset by about 30 degrees from Earth's orbital plane, reflecting the Eridians' different coordinate system. The filament connecting the center sphere (Tau Ceti) to another sphere corresponds to the star 40 Eridani, which Grace deduces is Rocky's home system. The message is clear: "We're from the 40 Eridani system. And now we're here at Tau Ceti." The presence of a Petrova-line model on both the main map and the miniature indicates that 40 Eridani also has an active Astrophage population, confirming that Rocky's species faces the same existential threat as humanity. Grace realizes that both civilizations independently built interstellar ships to investigate Tau Ceti's immunity, making them allies in a shared crisis.

Grace's Response

To reply, Grace modifies the model by soldering a piece of solder from the lab to the sphere representing Tau Ceti, then attaching the other end to the sphere representing Sol (Earth's sun). He then creates a crude Petrova-line icon out of hard paraffin and smushes it onto the Sol sphere. The result is a clumsy addition of a crayon-drawing quality to the sleek xenonite whiskers, but Grace judges it sufficient to convey that his star also has a Petrova line. He returns the model to Rocky via EVA, shoving it toward the Blip-A at about 2 meters per second, signaling that he can handle slightly faster deliveries. This exchange marks the transition from simple engine-flash signaling to symbolic communication, laying the groundwork for the development of a shared language.

Significance

The star map model is the first object that enables genuine two-way communication between humans and Eridians. It proves that both species are aware of Astrophage, that both are investigating Tau Ceti's immunity, and that both are willing to cooperate. The model's nested structure—a miniature Petrova line within the main map—suggests a recursive understanding of the problem, hinting that the solution may involve multiple scales of interaction. Grace's modification of the model with human materials demonstrates his willingness to engage in the conversation, while Rocky's subsequent response—a model of the two ships connected by a tunnel—shows that the Eridians understand the concept of a meeting. The star map model thus serves as the Rosetta Stone of first contact, enabling the partnership that ultimately saves both worlds.