Ben Bova: Titan

I had to kill you, Susie, Pancho said silently. So you could be reborn. And here you are, alive and healthy, all grown up, and suspicious as hell about your big sister.

This much is known about Titan, by far the largest of Saturn’s several dozen moons and the second largest moon in the entire solar system.

With a diameter of 5,150 kilometers, Titan is bigger than the planet Mercury and only a shade smaller than Jupiter’s largest satellite, Ganymede. Titan is the only moon in the solar system to possess a substantial atmosphere. Indeed, Titan’s atmosphere is 50 percent denser than Earth’s at ground level.

That atmosphere is composed mainly of nitrogen, laced with hydrocarbons such as methane, ethane and propane, plus nitrogen-carbon compounds such as hydrogen cyanide, cyanogen, and cyanoacetelyne. Shine sunlight on such an atmosphere and you get the same result you would in Los Angeles or Tokyo or Mexico City: photochemical smog, induced by solar ultraviolet light. Titan is a smog-covered world. Its predominantly orange coloring is due to this smog, which blankets Titan and makes it necessary for observations of its surface to be done in infrared wavelengths, which penetrate the smog, rather than visible light, which does not.

The incoming solar ultraviolet light, together with energetic electrons from nearby Saturn’s powerful magnetosphere, produce complex chemical reactions high in Titan’s thick atmosphere. Organic polymers called tholins are created, to drift downward deeper into the atmosphere and eventually fall onto the moon’s surface: black snow.

Laboratory experiments on Earth showed that tholins, when dissolved in liquid water, yield amino acids, which are the building-block molecules of proteins and thus fundamental to life.

Orbiting more than a million kilometers from Saturn, which in turn lies twice as far from the Sun as Jupiter and ten times farther from the Sun than the Earth does, Titan’s surface temperature averages -183° Celsius. Titan is cold, too cold to have liquid water on its surface—except when a region might be heated temporarily by a volcanic eruption or the impact of a meteor. Or if the water is mixed with an antifreeze compound, such as ammonia or ethane derivatives.

Titan’s density is not quite twice that of water, which means that its body must be composed largely of ices—frozen water and/or frozen methane—with perhaps a small rocky core beneath a thick icy mantle.

Despite Titan’s low temperature, liquid droplets of ethane can form in its atmosphere and rain down onto the frigid surface, collecting as lakes or perhaps larger seas. There are streams of ethane (or ethane-laced water) carving out channels across the ground of ices. Several sizable seas of hydrocarbon-crusted liquid methane dot the moon’s surface.

Titan rotates on its axis in slightly less than sixteen Earth days, the same period as its orbit around Saturn. Thus Titan is “locked” in its rotation so that it always presents the same face to its planet, Saturn, just as our Moon presents the same face to Earth. But even a “locked” moon wobbles slightly in its orbit, and Titan’s rotation is perturbed slightly by its sizable neighbors, the moons Rhea and Hyperion, each of which is close to 1,500 kilometers in diameter. Titan rocks slightly back and forth as it orbits Saturn, a ponderous wobbling that creates strange tides in its hydrocarbon seas.

A world rich in carbon, hydrogen and nitrogen. A world where raindrops of ethane and sooty flakes of tholins fall from the smoggy sky. A world that contains rivers and streams of ethane or ethane-laced water, and methane seas. Although it is a very cold world, a primitive form of microbial cryogenic biology was found to exist on Titan’s surface by the earliest automated probes from distant Earth. Could there be a more sophisticated biosphere, perhaps deeper underground?

And there are large swaths of dark material carpeting parts of Titan’s surface. Early probes showed that they are rich in carbon compounds. Fields of frozen petroleum? Patches of solidified hydrocarbons? Swales of black tholin snowbanks piled on ground that is too cold for them to melt?

Or something else?

Eduoard Urbain smiled uneasily as he shook hands, one by one, with each member of his scientific and engineering staffs. They shuffled themselves into a reception line the moment he entered the auditorium, like serfs of old lining up with their hats in their hands to receive the Christmas blessing of their lord and master.

Jeanmarie, standing beside him, smiled graciously and spoke a few words to every man and woman presented to her. She is wonderful, Urbain thought, as he shook hand after hand. She is in her element, kind and warm and loving. I would be lost without her. The line seemed endless, and Urbain struggled to find something worth saying, something more than “Merry Christmas” endlessly repeated.

At last it was done. Urbain rubbed his numbed hand and looked out over the assembly. Two hundred men and women, he thought. One hundred and ninety-four, to be precise. It is such a small number to run the scientific investigation of Saturn, its rings, and its moons. But when you must greet each one individually it seems like a very large number indeed.

Nadia Wunderly was one of the last persons that Urbain had greeted. She was the maverick among his scientists, and although she had brought Urbain sudden and unexpected success, he still regarded her with a mixture of disquiet and, yes, jealousy. She had refused to follow his orders and join the others in the study of Titan. Instead she had focused single-mindedly on Saturn’s rings. And discovered organisms living in their particles of ice. A great discovery, if it held true. Wexler and her ICU lackeys seemed to harbor some doubts about Wunderly’s claim.

Now Wunderly drifted from the reception line to the makeshift bar that had been set up along the base of the auditorium’s stage. She was a young woman, not yet thirty, with a rather pretty heart-shaped face. Urbain thought she would look even prettier if she stopped dying her hair brick red and let it grow normally instead of chopping it into those ridiculous barbs; her hair looked like the spiked end of a medieval bludgeon. She was wearing her usual dark tunic and slacks, which was unfortunate: Her figure was ample, too ample for his taste. Buxom, yes, but also heavyset, thick in the waist and limbs.

He mentally compared her to his wife. Slim and elegant, Jeanmarie would commit suicide before letting herself gain that much weight.

Wunderly was also looking at Jeanmarie Urbain. Slim as a stylus, she thought. One of those lucky women who had a metabolism that burned calories faster than she could ingest them. Probably never had to diet a day in her life. She can wear those frilly dresses and look gorgeous in them. I’d look like a hippopotamus in a tutu.

But that’s all changing, Wunderly told herself. I’ve dropped five kilos in the past two weeks and I’m going to lose another three before New Year’s Eve. Now for the real test.

One of the guys behind the bar offered her a cup of eggnog. Wunderly almost took it before she pulled her hand back and asked for mineral water, instead.

The guy—one of the technicians who worked with the Titan Alpha engineers—grinned at her. “One glass of genuine recycled local aitch-two-oh, courtesy of the waste management department,” he said cheerfully, handing her a glass.

Wunderly grinned at him. “You can’t scare me.”

He grinned back. “Ho, ho, ho and all that, Nadia.”

“Same to you,” she said, then walked away from the bar, into the milling throng.

The speakers set up at either end of the stage were pouring out syrupy Christmas tunes. Somehow they made Wunderly feel sad. Have yourself a merry little Christmas. Sure. A billion kilometers from home. Well, at least I can go home when I’m ready. Most of the poor slobs in this habitat can’t.