BALLOONS

BEFORE THE EXPLORERS LANDED ON THE SURFACE OF MARS, while they were still in orbit, goggling at the rusty worn immensity of the red planet, they released the balloons.

Six winecase-sized capsules retrofired from their orbiting supply vessel and blazed into the thin Martian atmosphere, then released a dozen balloons each. The balloons were brilliantly simple, little more than long narrow tubes of exquisitely thin yet tough Mylar inflated with hydrogen gas automatically when they reached the proper altitude to float across the landscape like improbable giant white cigarettes.

Dangling below each long, thin balloon was a “snake,” a flexible slim metal pipe that contained sensing instruments, radio, batteries and a heater to protect the equipment against the frigid weather.

By day the balloons wafted high in the Martian atmosphere, sampling the temperature (low), pressure (lower), humidity (lower still) and chemical composition of the air. The altitude at which any individual balloon flew was governed by the amount of hydrogen filling its slender cigarette shape. The daytime winds carried them across the red landscape like dandelion puffs.

At night, when the temperatures became so frigid that even the hydrogen inside the balloons began to condense, they all sank toward the ground like a chorus of ballerinas tiredly drooping. Often, the “snakes” of instruments actually touched the ground and dutifully transmitted data on the surface conditions each night while the balloons bobbed in the dark winds, still buoyant enough to hover safely above the rock-strewn ground. Barely.

Similar balloons had been a major success during the First Mars Expedition, even though many of them eventually snagged on mountainsides or disappeared for reasons unknown. Most drifted gracefully across the face of Mars for weeks on end, descending slowly each night and rising again when the morning sunlight warmed their hydrogen-filled envelopes, carrying on silently, effortlessly, living with the Martian day/night cycle and faithfully reporting on the environment from pole to pole.