Effortlessly at first, the Ra tracked the bathyscaphe as it descended into ever-thickening layers of Jovian air, followed by a swarm of camera drones. Bathyscaphe: that had been an archaic word even when Falcon was born, and yet it was apt, he thought, for what was this but a descent into a mighty ocean?
Soon Ra plunged through cloud level D, and into a gathering darkness. As the descent continued, the pressure and temperature steadily increased, and Falcon had Trayne call out regular readings. The Ra, of course, hanging under its envelope of heated hydrogen, was itself dependent on a balance of air temperature and pressure to stay aloft. The Ra was more advanced than the old Kon-Tiki and, thanks to technologies piloted in the oceanic air of Venus, could reach greater depths without risk of being crushed. Nevertheless, they had gone little more than two hundred kilometres—Orpheus’s descent had barely begun—when Falcon, reluctantly, called a halt.
“We’re safe to hover at this level,” he reported up to NTB-4, and through them up to Mission Control on Amalthea. “Regret I can’t follow you any further, Orpheus. All your systems look nominal, as far as I can tell.”
“Your company has been appreciated, Commander Falcon.”
In the monitor, Hans Young smiled. “Like all the best Machines, he’s programmed to be polite. Prepare to hold your station, Ra, and to deploy transmission relay gear.”
“Copy.”
Falcon and Trayne got to work transforming the Ra into a stationary radio relay post. Antennas unfurled around the envelope, including the long, trailing receptors that Falcon, on other days, used to communicate with his friends the medusae. But both of them kept an eye on the images, in visual light, radar and even sonar, of Orpheus’s descent into a thickening murk. Most of the camera drones still followed, but one or two, it seemed, were already failing as the conditions grew tougher, the images they returned fritzing to empty blue.
A key milestone came when Orpheus’s balloon envelope was cut away and allowed to drift off.
“Too deep for hot-air ballooning now,” Falcon muttered. “But look at the rate of descent. It’s hardly increased, even without the envelope. Air resistance, and the bathysphere’s own buoyancy, is enough to slow it now.”
“I don’t understand,” Trayne said, frowning. “I knew I shouldn’t have skipped those briefings at Anubis . . . Without the balloon, how will they bring Orpheus home?”
Falcon studied him. “I guess you haven’t been around Machines much. Trayne, he won’t be coming home—nor will the Charons who are guiding him. Any more than Mariner 4 ever came back from its flyby of Mars.”
“What?”
“Never mind.”
“That isn’t quite true, Commander,” said Charon 1. “Before his craft is finally destroyed—or rather before he is destroyed, there being no distinction between craft and passenger—Orpheus’s identity complex will be uploaded through the relay stations we will establish, including your own, and copies will be captured here at NTB-4 and at Amalthea. I understand that this kind of replication of minds gives humans no comfort, but it suffices for us if the copy is indistinguishable from the original. So you see, Dr. Trayne Springer, in a sense he will come home—”
A flare of light showed up in several of the monitor screens.
Trayne was startled. “What was that? Is there something wrong?”
Falcon shook his head. “He already reached the thermalisation layer. Where it’s so hot that anything that can be heat-destroyed, will be. Certainly anything organic. That is the ultimate limit for Jovian life.”
Hans Young said cautiously, “Well, the limit for the life forms we know of, Commander. That’s one objective of the descent. To see what’s down there . . .”
To challenge the planet’s greatest depths had been one of Howard Falcon’s dreams since the Kon-Tiki. He longed to follow Orpheus. He could only wait here and watch.
* * * *
The fall continued relentlessly. The pressure and temperatures recorded by the probe continued to mount, leaving one comparison after another in their wake: a higher pressure than the surface of Venus, higher than Earth’s deepest ocean trench.
And as the pressure gauge crept up towards two thousand atmospheres, the probe revealed another of its secrets. Its hull abruptly collapsed, and this time it was Falcon who thought some catastrophic failure had befallen it. But the handful of remaining cameras, specialised for depth, showed that while the spherical hull had imploded, a kind of open framework survived, a space-filling, regular arrangement of bars and nodes.
“You see the design philosophy,” Hans Young said. “We do not fight the pressure, we yield to it. Though the Jovian air has flooded what was the interior, the craft still has some buoyancy, with small, very robust ballast tanks embedded deep in the surviving structure.”
“And I too survive,” reported Orpheus. “Along with the Charons, downloaded onto chips of diamond. We are comfortable.”
“Show-off,” Falcon muttered.
The probe plummeted through one cloud layer after another, as exotic species of molecules congealed out of the thickening air. But the light faded quickly, and soon the last and sturdiest of the camera drones fell away, and no more visible-light images were returned.
At about five hundred kilometres deep, the level once believed to have corresponded to Jupiter’s “surface,” Orpheus’s probing with radar, sonar and other sensors revealed the presence of masses of some kind drifting in the air, lumpy, granular. Quasi-solid “clouds” in an air of impossible density, Falcon speculated, which had perhaps fooled earlier observers into thinking this was a solid crust.
But Orpheus soon passed through this intriguing layer and fell deeper yet. The dense hydrogen air through which he fell now seemed featureless—and lifeless, lacking the sunlit glamour of the high clouds of the medusae. Time passed. Falcon was sure that reports on this stunt were being transmitted across the solar system, but he wondered how many viewers in their domes on Triton, or in the gardens of Earth, would be tuning out when the reports of this dull phase of the mission were sent to them at lightspeed’s crawl.
The next milestone came at one thousand kilometres deep.
“Pressure of eighty thousand atmospheres,” Orpheus reported. “Temperature eight hundred Kelvin. Pressure and temperature profiles have largely matched theoretical models so far. However the hydrogen-helium slush outside the hull is now more usefully described as a liquid rather than a gas . . .
“This is Orpheus. We are through the transition zone, and have reached Jupiter’s ocean of molecular hydrogen. The first sapients ever to do so.”
Falcon glanced at Trayne. “I’m sure I can hear a trace of pride in that voice.”
Trayne shrugged. “Why not?”
“Phase one is complete. A further layer of hull will be discarded; my descent will continue, while Charon 2 remains at this waystation.”
“I can confirm that,” called a new Machine voice: Charon 2. “I am ready to take up my station-keeping duties here.”
And Falcon was astonished by what Charon 2 said next:
“Godspeed, Orpheus.”
The descent continued.