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The orbit of Titan around Saturn is not a perfect circle。 it's noticeably squashed out； or elliptical。 If Titan has extensive oceans； though； the giant planet Saturn around which it orbits will raise substantial tides on Titan； and the resulting tidal friction will circularize Titan's orbit in much less than the age of the Solar System。 In a 1982 scientific paper called 〃The Tide in the Seas of Titan；〃 Stanley Dermott； now at the University of Florida； and I argued that for this reason Titan must be either an all…ocean or an all…land world。 Otherwise the tidal friction in places where the ocean is shallow would have taken its toll。 Lakes and islands might be permitted； but anything more and Titan would have a very different orbit than the one we see。
We have； then； three scientific arguments—one concluding that this world is almost entirely covered with hydrocarbon oceans； another that it's a mix of continents and oceans； and a third requiring us to choose； counseling that Titan can't have extensive oceans and extensive continents at the same time。 It will be interesting to see what the answer turns out to be。
What I've just told you is a kind of scientific progress report。 Tomorrow there might be a new finding that clears up these mysteries and contradictions。 Maybe there's something wrong with Muhleman's radar results； although it's hard to see what it might be： His system tells him he's seeing Titan when it's nearest； when he ought to be seeing Titan。 Maybe there's something wrong with Dermott's and my calculation about the tidal evolution of the orbit of Titan； but no one has been able to find any errors so far。 And it's Bard to see how ethane can avoid condensing out at the surface of Titan。 Maybe； despite the low temperatures； over billions of years there's been a change in the chemistry； maybe some bination of ets impacting from the sky and volcanoes and other tectonic events； helped along by cosmic rays； can congeal liquid hydrocarbons； turning them into some plex organic solid that reflects radio waves back to space。 Or maybe something reflective to radio waves is floating on the ocean surface。 But liquid hydrocarbons are very underdense： Every known organic solid； unless extremely frothy； would sink like a stone in the seas of Titan。
Dermott and I now wonder whether； when we imagined continents and oceans on Titan； we were too transfixed by our experience on our own world； too Earth…chauvinist in our thinking。 Battered； cratered terrain and abundant impact basins cover other moons in the Saturn system。 If we pictured liquid hydrocarbons slowly accumulating on one of those worlds； we would wind up not with global oceans； but with isolated large craters filled； although not to the brim； with liquid hydrocarbons。 Many circular seas of petroleum； some over a hundred miles across； would be splattered across the surface—but no perceptible waves would be stimulated by distant Saturn and； it is conventional to think； no ships； no swimmers； no surfers； and no fishing。 Tidal friction should； we calculate； be negligible in such a case； and Titan's stretched…out； elliptical orbit would not have bee so circular。 We can't know for sure until we start getting radar or near…infrared images of the surface。 But perhaps this is the resolution of our dilemma： Titan as a world of large circular hydrocarbon lakes； more of them in some longitudes than in others。
Should we expect an icy surface covered with deep tholin sediments； a hydrocarbon ocean with at most a few organic encrusted islands poking up here and there； a world of crater lakes； or something more subtle that we haven't yet figured out？ This isn't just an academic question； because there's a real spacecraft being designed to go to Titan。 In a joint NASA/ESA program； a spacecraft called Cassini will be launched in October 1997—if all goes well。 With two flybys of Venus； one of Earth； and one of Jupiter for gravitational assists； the ship will； after a seven…year voyage； be injected into orbit around Saturn。 Each time the spacecraft es close to Titan； the moon will be examined by an array of instruments； including radar。 Because Cassini will be so much closer to Titan； it will be able to resolve many details on Titan's surface indetectable to Muhleman's pioneering Earth…based system。 It's also likely that the surface can be viewed in the near infrared。 Maps of the hidden surface of Titan may be in our hands sometime in the summer of 2004。
Cassini is also carrying an entry probe； fittingly called Huygens； which will detach itself from the main spacecraft and plummet into Titan's atmosphere。 A great parachute will be deployed。 The instrument package will slowly settle through the organic haze down into the lower atmosphere； through the methane clouds。 It will examine organic chemistry as it descends； and—if it survives the landing—on the surface of this world as well。
Nothing is guaranteed。 But the mission is technically feasible； hardware is being built； an impressive coterie of specialists； including many young European scientists； are hard at work on it； and all the nations responsible seem mitted to the project。 Perhaps it will actually e about。 Perhaps winging across the billion miles of intervening interplanetary space will be； in the not too distant future。 news about how far along the path to life Titan has e。
CHAPTER 8 THE FIRST NEW PLANET
1 implore you； you do not hope to be able to give the reasons for the number of planets； do you？ This worry has been resolved 。 。 。
— JOHANNES KEPLER； EPITOME OF COPERNICAN ASTRONOMY； BOOK 4 / 1621
Before we invented civilization； our ancestors lived mainly in the open； out under the sky。 Before we devised artificial lights and atmospheric pollution and modern forms of nocturnal entertainment； we watched the stars。 There were practical calendrical reasons； of course； but there was more to it than that。 Even today； the most jaded city dweller can be unexpectedly moved upon encountering a clear night sky studded with thousands of twinkling stars。 When it happens to me after all these years； it still takes my breath away。
In every culture； the sky and the religious impulse are intertwined。 I lie back in an open field and the sky surround me。 I'm overpowered by its scale。 It's so vast and so far away that my own insignificance bees palpable。 But I don't feel rejected by the sky。 I'm a part of it； tiny； to be sure； but everything is tiny pared to that overwhelming immensity； And when I concentrate on the stars； the planets； and their motions； I have an irresistible sense of machinery； clockwork； elegant precision working on a scale that； however lofty our aspirations； dwarfs and humbles us。
Most of the great inventions in human history—from stone tools and the domestication of fire to written language—were made by unknown benefactors。 Our institutional memory of long…gone events is feeble。 We do not know the name of that ancestor who first noted that planets were different from stars。 She or he must have lived tens； perhaps even hundreds of thousands of years ago。 But eventually people all over the world understood that five； no more； of the bright points of light that grace the nig