The high-pressure zone created by the wind now had an avenue to drain. The breach widened more and more with each passing millennium. As it widened, dust and sand particles carried along with the attack settled in the basin below.

Eventually, a balance point was reached. The sand had piled up high enough to be flush with the land outside the crater. It no longer built upward but outward. The slope lengthened until a new balance point was reached, one defined by the complex interactions of countless tiny particles and their ability to maintain an angled shape. Entrance Ramp had been born.

The weather brought dunes and desert terrain. Nearby crater impacts brought rocks and boulders. The shape became uneven.

Gravity did its work. The ramp compressed over time. But it did not compress evenly. Differing densities shrunk at different rates. Some areas became hard as rock while others remained as soft as talc.

While providing a small average slope into the crater, the ramp itself was rugged and bitterly uneven.

On reaching Entrance Crater, the lone inhabitant of Mars turned his vehicle toward the Schiaparelli Basin. The difficult terrain of the ramp was unexpected, but it looked no worse than other terrain he routinely navigated.

He went around the smaller dunes and carefully crested the larger ones. He took care with every turn, every rise or fall in elevation, and every boulder in his path. He thought through every course and considered all alternatives.

But it wasn’t enough.

The rover, while descending down a seemingly ordinary slope, drove off an invisible ridge. The dense, hard soil suddenly gave way to soft powder. With the entire surface covered by at least five centimeters of dust, there were no visual hints to the sudden change.

The rover’s left front wheel sank. The sudden tilt brought the right rear wheel completely off the ground. This in turn put more weight on the left rear wheel, which slipped from its precarious purchase into the powder as well.

Before the traveler could react, the rover rolled onto its side. As it did, the solar cells neatly stacked on the roof flew off and scattered like a dropped deck of cards.

The trailer, attached to the rover with a tow clamp, was dragged along. The torsion on the clamp snapped the strong composite like a brittle twig. The hoses connecting the two vehicles also snapped. The trailer plunged headlong into the soft soil and flipped over on to its balloon-roof, shuddering to an abrupt halt.

The rover was not so lucky. It continued tumbling down the hill, bouncing the traveler around like clothes in a dryer. After twenty meters, the soft powder gave way to more solid sand and the rover shuddered to a halt.

It had come to rest on its side. The valves leading to the now- missing hoses had detected the sudden pressure drop and closed. The pressure seal was not breached.

The traveler was alive, for now.

CHAPTER 24

THE DEPARTMENT heads stared at the satellite image on the projection screen.