Scandinavia & 

 Northern Europe 



10- to 38-day CruiseTours " 



fror 



$ 



1,599 



Captivating CruiseTours visit lands of 

 castles, souring fjords and Viking chieftains 



and explore cities like Stockholm, 

 Helsinki, St. Petersburg and Tallin. All at 

 a relaxed pace aboard the av^^ard-winning 

 Marco Polo, with plenty of time ashore. 



You'll also enjoy hotel stays in 

 Copenhagen, London and/or Reykjavik, 

 Iceland. Discover for yourself 

 why Orient Lines is known as 

 "The Destination Cruise Specialists". 



Orient LiNES^ 



THE DESTINATION CRUISE SPECIALISTS 



www.orientlines.com 



For reservations, see your travel agent, 

 for brochures, call 1-800-333-7300. 



'hie IS ihown in U.S. doilan for CniiicTour only, per person, bucd on double ocaipjna, 



for 3 minimuni atcgory inside sutcroom and appliubic on selea sailings. Airfare is 

 addirional lo CruiseTour fare, avaibbic from «lca U.S. citio and departure uxes may apply. 

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 capacity controlled, not combinable with other offers, subjca to change without notice and 

 may be withdrawn at any time. Orient Lints is not responsible for typographical em»rs or 

 t. Ship's Registry. Bahamas. 0 2005 Na Corporation Ltd. All Ri^is RoersiJ. 



with us." Within a few days, however, 

 she discovered other repeating signals 

 coming from other places in our galaxy. 

 Bell and her associates realized they'd 

 discovered a new class of cosmic ob- 

 ject — pulsing stars — which they clev- 

 erly, and sensibly, called pulsars. 



Turns out, intercepting radio 

 waves isn't the only way to be 

 snoopy. There's also cosmochemistry. 

 The chemical analysis of planetary 

 atmospheres has become a lively field 

 of modern astrophysics. Cosmochem- 



snooping aliens would need to build a 

 spectrometer to read our fingerprints. 

 But above all. Earth would have to 

 eclipse its host star (or some other light 

 source), permitting light to pass through 

 our atmosphere and continue on to the 

 aliens. That way, the chemicals in Earth's 

 atmosphere could interact with the 

 Hght, leaving their marks for all to see. 



Some molecules — ammonia, carbon 

 dioxide, water — show up everywhere 

 in the universe, whether life is present 

 or not. But others pop up especially in 

 the presence of life itself. Among the 



Among the biomarkers for aliens 

 to ponder in Earth '5 atmosphere: 

 chlorofluorocarbons, vapor from mineral 

 solvents, escaped coolants, and smog 



istry depends on spectroscopy — the 

 analysis of hght by means of a spec- 

 trometer, which breaks up light, rain- 

 bow st\'le, into its component colors. 

 By exploiting the tools and tactics of 

 spectroscopists, cosmochemists can in- 

 fer the presence of life on an exoplan- 

 et, regardless of whether that life has 

 sentience, intelligence, or technology. 



The method works because every 

 element, every molecule — no matter 

 where it exists in the universe — 

 absorbs, emits, reflects, and scatters light 

 in a unicjue way. Pass that light through 

 a spectrometer, and you'll find features 

 that can rightly be called chemical fin- 

 gerprints. The most visible tingerpnnts 

 are made by the chemicals most excit- 

 ed by the pressure and temperature of 

 their environment. Planetary atmos- 

 pheres are crammed with such features. 

 And if a planet is teeming with flora and 

 fauna, its atmosphere will be crammed 

 with biomarkers — spectral evidence of 

 life. Whether biogenic (produced by 

 any or all life-forms), anthropogenic 

 (produced by the widespread species 

 Homo sapiens), or technogenic (pro- 

 duced only by technology), this ram- 

 pant evidence will be hard to conceal. 



Unless they happen to be born with 

 built-in spectroscopic sensors, space- 



biomarkers m Earth's atmosphere are 

 ozone-destroying chlorofluorocarbons 

 from aerosol sprays, vapor from miner- 

 al solvents, escaped coolants from re- 

 frigerators and air conditioners, and 

 smog from the burning of fossil friels. 

 No other way to read that list: sure signs 

 of the absence of inteUigence. Anoth- 

 er readily detected biomarker is Earth's 

 substantial and sustained level of the 

 molecule methane, more than halt of 

 which is produced by human-related 

 activities such as tuel-oil production, 

 rice cultivation, sewage, and the burps 

 of domestic livestock. 



And if the aliens track our nighttime 

 side while we orbit our host star, they 

 might notice a surge of sodium from 

 the sodium-vapor streetlights that 

 switch on at dusk. Most telling, how- 

 ever, would be all our tree-floating 

 oxs'gen, which constitutes a tull fifth 

 of our atmosphere. 



Oxygen — which, after hydrogen 

 and helium, is the third most 

 abundant element in the cosmos — is 

 chemically active and bonds readily 

 with atoms of hydrogen, carbon, nitro- 

 gen, silicon, sulfur, iron, and so on. 

 Thus, for oxygen to exist in a steady 

 (Coiitimied on page 55) 



22 



NArui<.AL HISTORY February 2006 



