Titan Read Online Free PDF Page B

it.
    Before the end of that party she’d buttonholed Rosenberg and arranged to meet him here, at JPL. She’d figured it was a better than evens chance that he would have forgotten all about her, in which case she would have driven all this way out here to the arroyo for nothing. But when she’d arrived at the security gate, she found he’d left a media pass for her to collect.
    Soon the softscreen was covered by chemical, notation and complex molecular structure charts.
    He said, “How much biochemistry do you know?”
    Actually, she’d picked up a little in her graduate days. But she said, “Nothing.”
    “All right. I’m working in the group responsible for the GCMS results.”
    “GCMS?”
    “Gas chromatograph and mass spectrometer. In-situ measurements of the chemical composition of gases and aerosols in Titan’s atmosphere, and at the end of Huygens’ s descent, a direct sample of the surface. The lead scientist is a guy at Goddard. On the lander, a slug sample was drawn in through filters and into an oven furnace, which—”
    “Enough. Tell me what y ou do.”
    “I’m working on high atomic number results. Complex molecules. Look—what do you know about conditions on the surface of Titan?”
    “Only what I’ve seen in the pop press the last few weeks.”
    “All right. Titan is an ice moon, with a thick layer of atmosphere. The only moon with a significant layer of air, anywhere. In a lot of ways, Titan right now is like primeval Earth—say, four and a half billion years ago. Its chemistry is mostly based around carbon, hydrogen and nitrogen. And chemistry like that produces a lot of the key molecules of prebiotic chemistry.”
    “Prebiotic?”
    “The components of life. But there’s a crucial difference. Titan has no liquid water. It’s too cold for that. The importance of water on primitive Earth is that it was a solvent. It allowed the polymerization of volatile reactive organics and the hydrol ysis of prebiotic oligomers into biomolecules… I’m sorry. Look, you need water as a solution medium, so that the components, the building blocks, can assemble themselves into proteins and nucleic acids, the main macromolecules of our form of life.”
    Our form of life. That phrase made her shiver. “But maybe there are other solvents.”
    “Correct. Maybe there are other solvents. In particular, ammonia. And we knew before Huygens that there is ammonia on Titan. Now. Look here. Look what the Huygens GCMS found.” He pointed to a diagram of a molecule shaped like a figure eight on its side, with some of its edges highlighted in blue for double covalent bonds.
    “What is it?”
    “Ammono-guanine. That is, guanine with the water chemistry systematically replaced by ammonia.” He looked up at her, the multicolored diagram reflected in his glasses. “Do you get it? Exactly what we’d have expected to have found, if some ammonia-based analogue of terrestrial life processes was going on down there. Look at these ratios.” He pulled up another image. “See that? Here, close to the surface, you have a depletion of methane and gaseous nitrogen, and a surplus of ammonia and cyanogen, compared to the atmosphere’s average. The analogy is clear. Methane and nitrogen are being used in place of monose sugars and oxygen, and you have ammonia and cyanogen instead of water and carbon dioxide—”
    “What are you saying, Rosenberg?”
    “Respiration,” he said. “Don’t you get it? Something down there has been breathing nitrogen, and exhaling ammonia.”
    “So, could it mean life?”
    He looked puzzled by the question. “yes. That’s the point. Of course it could.”
    She frowned, staring at the molecular imagery. It was exciting, yes, but it was hardly the electric thrill she’d been hoping for. Even those blurred images of the microfossils in that mete orite from Mars had had more sex appeal than this obscure stuff.
    “What do you think we should do about this?”
    “Send another probe, of