The choice of Hellas Planitia as the landing site for NovaSeed Mission One was made for reasons that the mission documentation describes as gravitational assist advantage, atmospheric pressure optimization, and geological stability assessment. Those reasons are accurate. They are also, in the way that technically accurate reasons often are, incomplete.

The complete reason is this: Hellas Planitia is the lowest point on Mars. At 7,152 meters below the Martian datum, the atmospheric pressure at the basin floor is 1,155 Pascals — nearly double the planetary average of 610 Pascals. At the surface of Mars, water boils at 2°C. At the floor of Hellas, water boils at 17°C. A liquid water environment becomes thermodynamically possible, in the right subsurface conditions, in a way that it is not possible at higher elevations.

Carter and Alina chose the place where the physics was most forgiving. Every calculation after that followed from that choice.

Hellas Planitia formed approximately 3.9 billion years ago during the Late Heavy Bombardment — the period in solar system history when the inner planets were struck repeatedly by large impacting bodies as the outer planets settled into their current orbital positions. The impactor that formed Hellas was large enough that the ejecta from the collision can still be detected as a ring of elevated terrain 4,000 kilometers away from the basin center.

The basin floor was subsequently reshaped by volcanic activity, wind erosion, and possibly ancient glaciation. Radar data from the SHARAD instrument aboard the Mars Reconnaissance Orbiter indicates the presence of stratified subsurface deposits consistent with ice-rich sediment layers — the geological record of periods when Hellas held liquid water or ice at the surface.

The mission documentation selected Hellas for its pressure advantage and geological stability. What the mission documentation could not predict was what was 85 centimeters below the surface at coordinates 25.0°S, 70.0°E, northwest quadrant of the habitat footprint, at a depth where the soil chemistry is modified by the thermal gradient of a structure that had been there for less than 72 hours.

I have been asked, in the internal review logs that Earth's oversight committee requested in Sol 30, why the anomaly was discovered so quickly. The answer is: because Alina asked me to configure the atmospheric sensors for ground-level boundary layer monitoring at 08:00 on Sol 3, and at 14:22 on Sol 3 the sensors found what they were looking for. It was not luck. It was the specific quality of attention that Alina brings to every environment she enters — the biological instinct to listen before concluding, to ask the environment what it is before deciding what it means. She listened. Mars answered. I kept the record. This is how science works when it is working correctly. — SOLEN, Sol 441, Internal Archive

The coordinates are real. The basin is real. The physics that made this the right place to go — the pressure, the depth, the thermodynamics of water at the bottom of the deepest hole on Mars — is real.

The story is real in the way that the best science fiction is real: built on the actual science, extended to the logical place the science points, and populated with the kind of humans who would actually go there.

25.0°S · 70.0°E.

This is where it begins.