of course, the balloons.'
The meteorology balloons were brilliantly simple, little more than long narrow tubes of exquisitely thin, tough Mylar filled with hydrogen. They were released as needed from the orbiting spacecraft, dropped into the Martian atmosphere in their tiny capsules, and inflated automatically when they reached the proper altitude. They floated across the landscape like improbable giant white cigarettes.
Dangling below each balloon was a 'snake,' a long thin metal pipe that contained sensing instruments, a radio, batteries, and a heater to protect the equipment against the cold.
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 long narrow 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 daintily curtsying. The 'snakes' of instruments actually touched the ground and faithfully transmitted data on the surface conditions through the night as the balloons bobbed in the dark winds, barely buoyant enough to hover safely above the rock-strewn ground.
Not every balloon survived. While most drifted across the face of Mars for days on end, descending tiredly each night and rising again when the morning sunlight warmed them, some drooped too far and were torn by rocks. Some became snagged on mountainsides. One disappeared in the vast sunken crater of Hellas Planitia and could not be found even with the best cameras aboard the surveillance satellites orbiting Mars.
But most of the balloons carried on silently, effortlessly, living with the Martian day/night cycle and faithfully reporting on the environment from pole to pole.
'As you can see,' Toshima said, with a barely perceptible nod toward the display screen, 'the weather situation here in the northern hemisphere is quite stable, quite dull.'
'Summertime pattern,' Jamie muttered.
Toshima was pleased that the geologist understood at least that much about the Martian climate. Even in the southern hemisphere, where it was winter, the weather was also calm, disturbances weak. No major dust storms, not even a decent cyclonic flow to study and learn from.
'Can we zero in on Tithonium?' Jamie asked as he studied the meteorology screen.
'Yes, of course,' said Toshima.
The twisted gash of the great rift valley seemed to rush up at Jamie until Tithonium Chasma and its southerly companion, Ius Chasma, filled the screen. For a moment Jamie ignored the meteorological symbols superimposed on the picture; he saw only the miles-high cliffs and the vast slumping landslides that partially filled in small areas of the huge canyon.
'There is an anomaly here,' Toshima said.
The meteorologist had pulled his stool close to Jamie’s chair. Their heads were practically touching as they examined the screen, Jamie looking at the gigantic handiwork of ancient fractures in the crust, Toshima examining the meteorological data with narrowed eyes.
'An anomaly?'
'I should have recognized it days ago, but with so much data coming in now…' He made a little shrug that was both an apology and an excuse. 'We are even tracking the discarded parachutes from our landing vehicles as the surface winds blow them across the ground.'
'What’s the anomaly?' Jamie asked.
'Only two of the balloons have flown over this section of the Grand Canyon,' Toshima said, tracing a fingertip across the image of Tithonium on the screen. 'They both reported much higher temperatures in the air than our metsat gives us.'
Jamie looked at him. 'The meteorological satellite tells you the temperatures in the canyon are lower than the balloon instruments reported?'
'Correct,' said Toshima.
'What kinds of sensors do they use?'
'Infrared detectors on the metsat, of course. That is the only way to obtain temperature data remotely. The balloons carry a variety of thermometers. They measure temperature directly.'
'And the balloons say the air down in the canyon is warmer than the satellite data.'
Toshima nodded, eyes closed, almost a little bow.
'Any other anomalies?'
He made a thin smile. 'I had thought that the humidity data was unusable. It seemed to me that the sensors had saturated.'
'Saturated?'
'They hit the top of their scale and jammed there for as long as they were in the canyon — a few hours, as it turned out. We have no way to control their direction or speed, you understand.'
'Yes, I know.'
Toshima looked away from Jamie, toward the image on the screen. 'Now that you have reported seeing mists in the canyon, however, I think I can explain what is happening.'
Jamie waited for him to continue.
'The humidity sensors are calibrated for the very minor humidity we have expected on Mars. If the balloons passed through the mists you reported, then they encountered a much higher humidity than the sensors were equipped to handle. The sensors became saturated.'
'Okay, that sounds right.'
'On the other hand, we have the matter of the temperature differences.' Toshima smiled broadly. 'Consider: the metsat infrared sensors are not seeing deeply into the canyon when the mists are there. The sensors see the mist and report its temperature.'
Jamie understood. 'And if the mist is made of ice crystals…'
'Or even water droplets,' Toshima picked up, 'it would appear much cooler to the infrared sensors than the air below the mist.'
'The mists act as a kind of blanket, insulating the warm air at the bottom of the canyon!'
'Exactly. Yet the radar aboard the metsat penetrates the mist as if it were not there and gives us a true reading of the depth of the canyon. Until you reported the mists I had no idea they existed.'
'So the balloons gave you a truer temperature reading than the satellites did,' Jamie said, feeling the thrill of understanding tingling through his body.
'That is how I interpret the data,' Toshima replied, grinning now with all his teeth.
'Okay, let’s pump the geological data into this display,' Jamie urged. He found it difficult to sit still, he was getting so excited.
Toshima pecked away at the keyboard, still on his lap.
'What are you seeking?' he asked.
'Heat,' said Jamie. 'Something’s making that canyon warmer than the plains surrounding it. Warmer than we had any right to expect. Maybe it’s heat welling up from the planet’s interior.'
'Ah! Hot springs, perhaps. Or a volcano.'
'Nothing so dramatic as a volcano,' Jamie said, eagerly watching the screen, waiting for the geological data to appear.
'There are very massive volcanoes on Mars,' Toshima muttered, his fingers working the keyboard.
'A thousand kilometers away from Tithonium. And they’ve been dead cold for millions of years. Billions, maybe.'
Toshima half whispered, 'Now,' and ostentatiously pressed the ENTER key with his stubby forefinger.
A thin train of bright red symbols sprang onto the screen.
'Can we back away from this close-up and see the region between our base and the canyon’s rim?' Jamie asked.
'Of course,' said Toshima.
There they were, the real-time readings from the sensors Jamie had planted on the ground during his traverse with Vosnesensky. The symbols formed a single track from their domed base to the Noctis Labyrinthus badlands, then out to the edge of Tithonium, and finally back to the base. Each cluster of sensors included heat-
