Ca Li for Ni a Insc Itu Te of Techno Logy Voillme LX, Nllmber 3, I 997
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Ca li for ni a Insc itu te of Techno logy SC I EN CE Voillme LX, Nllmber 3, I 997 IN THIS ISSUE Water and Ancient Mars Geology Under the Antarctic Ocean Arsenic and the L.A . Aqueduct Top: Every explorer wants to see what's on the other side of the next hill. When Sojourner, the Mars Path finder's rover, peered over a nearby crest on Sol (Mar- tian day) 76, it saw what appear to be sand dunes. If the stuff really is sand (a question that is still being debated), it implies the likely long-term prese.nce of liquid water-the most plausible agent for creating sand-sized grains. The Twin Peaks are on the horizon on the right; the "Big" Crater is on the left. Bottom: The rover took this picture of the lander, nesting comfortably in its deflated air bags, on Sol 33. You can see the for ward ramp, which sticks straight out like a diving board instead of bending down to touch the Martian surface (the rover drove off the rear ramp). And if you think you see E.T.'s face, you're not far wrong Pathfinder's camera has two "eyes" spaced 15 cen timeters apart for stereo vision. For a look at what else Pathfinder has seen, turn to page 8. " N GIN E E R I N G & C 1 ENe E Ca li for n ia Instit u te o f Tec h no logy 2 Random Wa lk 8 Pathfinder's Fi n ds - by Dougla s L. Smi t h Twenty-one years after the Vi king land ings, JPL has once again set foot on rhe red planet- a place both stranget and more Earthli ke than we had imagined. 18 Geophysi c al Secrets Be n eath Antarctic Wate r s - by Joann M . Stock These icy seas may hold the key to reconstructi ng ancient plate mig rations. 28 So lar Fue l - by Harry B. Gray Scientists are laboring to do what plants have been doi ng for aeons-make dean fu el from sunlig ht. 34 Chinatow n Revisi t ed: Arsenic and th e Lo s Ange les Wate r S u p ply - by Janet G. Hering On the cover: The early What is arsenic doi ng in our water, and should we be worried about it? morning sun glints off the A chemical detecrive story. ice in Antarctica's Ross Sea. As the penguins frolic, a 41 Obituar ies: Eugen e Shoemaker group of Calt ech scientists is using shipboard geo 43 Fac ulty Fi le physical techniques to examine the seafloor fo r clues to the tectonic Engi neeri ng & Science (ISSN 001 3-7812) is published Thomas J . Tyson plates' motions. How the quarterly at the California Institute of Technology, 1200 Presidml of lhe A/llllllli AJJfxinlioll Antarctic and Pacific plates East California Boulevard, Pasadena, CA 9 1 125. Annual ]. Ernest N unnally subscription $ 10.00 domestic, $20.00 foreig n air mail; have wand ered with Vice Presidelll /0 1" Imlilllte Relntiom single copies $ 3.00. Send subscriptions co C"lltech 1-7 1, Roben 1. O 'Rourke respect to each other has Pasadena, CA 91 125. Third class postage paid at Pa...mde AJSocinte Vice Presidelll fo r /llstitllte Relatiom consequence's elsewhere na, CA. All rights reserved. Reproduction of material con rai ned herein fo rbidden wirhout authori7.ation. © 1997, STAFF: Editor - Jane Dietrich where the Pacific plate Califo rnia Jnstitu[c of'rechnology. Published by Caltech Managing Editor - Doug las Smith rubs past North Am el'ica, and the Alumni Association. Telephone: 626-395-3630. Contributing \Vrifer - Robert Tindol for example. The story of Copy Editol1 - Mi chael Farq uhar, PICT URE CR EDITS: Cove r, 18 , 22-24, 27 - Katrin Hafner; J ulie Hakewill what these scientists inside front cover, 8-16 - NASA; 2 - Doug Smith; 6, 7 - Wayne BIIS;IIess "'lalldger - Debbie Bradbury found, and what life Waller; 22,27 - Joann Stock; 28, 30, 33 - Bob Pn; 30-33- Cirm/afioll Malinger - Susan Lee Ben Ramirez; 31, 32 - J ay Winkler; .34,37,38,40 - Janet Her PhofograjJher - Robert Paz aboal'd a reseal'ch ship is ing , J en ni fer Wilkie; 35-37, 40 - Los Angck-s DWP; 41 - Judy like, begins on page 18. Amis; 4 2 - EltOn Sewell; inside back cOver - Herb Shocbridge Visit Calcech on the Web at http ://www.caltech.ed u Bill Johnson shows off a prototype putter whose head is one solid piece of metallic glass. The pizza paddle behind him is actually the biggest chunk of metallic glass ever cast, and is typical of the ingots from which the dub-face inserts are cut. they're called, absorb energy material, and it becomes as Random Walk FORE! that would otherwise be brittle as a common ceramic. imparted to the ball. (Ulri Try teei ng off with a porce mately, of course, if you put lain golf club! Tiger Woods doesn't really enough stress on the metal In order to make chunks need them, and the average the slippage leads to metal instead of ribbons, you'd have duffer probably can't afford fatigue and fractures.) So to figure out how to cool the them, but a new set of golf if you could get rid of the melt at a more reasonable clubs that can easily add ten crystalline structure, you'd rate-a few degrees per yards or more to your drive is get a much stronger, more second, say- while still coming on the market. The flexible metal that can take forestalling crystallization. "When the li quid becomes reason you 're reading about high stresses without absorb Arakan Peker (PhD '94) did them in Engineering & Science ing energy. (You'd get other just that in his thesis, says complicated enough, it can't instead of GoljDig,,' (where interesting properties as Johnson. "He realized that they'll appear next monch) is well-see E&S, Winter we had to go to a very com figure out how to crystallize that these clubs have a face, 1990.) plicated material. We need because there aren't any nice, or striking surface, made of Metallic glasses, however, to have four or more atoms a metallic glass developed by are amorphous, not crystal with different chemical simple, orderly patterns it can Cal tech researchers and trade line. Like a big paper bag characteristics before the named Liquidmetal. This stuffed full of golf balls, the liquid gets sufficiently settle inco, and while i t 's stuff is perfectly elastic, says atoms are loosely jumbled, frustrated in its efforts to William Johnson (PhD '75), with no regular pattern to crystallize. W hen the liquid thinking about it, we can cool the Mettler Professor of their arrangement- no neat becomes complicated enough, Engineering and Applied arrays. A glass is really just it can't figure out how to it enough co solidify it." Science. To prove it, he drops a very cold liquid in that crystallize because there aren't a ball bearing on a titanium respect, bur an extremely any nice, simple, orderly pat p late-the high-tech metal viscous one-the atoms are terns it can settle into, and of choice for golf-club heads. packed so densely that they while it's thinking about it, The bearing bounces perhaps aren 't free to move or flow. we can cool it enough to a dozen times. When the Amorphous metal ribbons solidify it. We might call demonstration is repeated less than a tenth of a millime this the 'confusion prin with a Liquidmetal plate, ter thick have been on the ciple.'" Peker used a five the bearing bounces like a market since 1973, bur that's metal mixture of zirconium, Superball. all that has been available titanium, nickel, copper, and Ordinary metals are crystal until now. Ordinary metals beryllium, but even th~t only line- as the melt cools, the crystallize so incredibly glassifies over a very narrow atoms snuggle together in rapidly that bypassing the range of compositions. In eat, orderly arrays. When process means cooling the But why take this marvel you apply stress to the metal melt by a million degrees per ous material and make golf -by hitting a golf ball with second or more, which can dubs? Well, you've got to it, for example-one plane of only be done with very thin start somewhere. And, says atoms slips partially our of layers of metal. And the Johnson, "golf is a very alignment with the neighbor cooling has to be rigorously demanding application. ing plane, creating the equiv uniform throughout the When a good golfer hits the alent of a wrinkle in a rug. piece- a few scattered crys ball, the dub head is moving These dislocation defects, as tals in the interior of the at 100-110 miles per hour, 2 ENGINEERING & HlfN(f NO. 199 7 and you do this thousands of times over the life of the club." Casting a club head is no stroll down the fairway, either--drivers are hollow, irons are concave in back, and even the simple slab of the humble putter is problemati caL The trouble is that the metallic-glass-forming melt is a hundred to a thousand times more viscous than an ordinary molten metal alloy. "1t's more like a thermoset GOOD NEWS AND BAD NEWS FOR MARTIAN MARINERS ting polymer," says Johnson. "Ie doesn't flow very well. Bubbles don't float; debris doesn't sink." David Lee (PhD '94) and Michael Ten hover (MS '78, PhD '81) had to develop an entirely new set The good news is that Mars deep within the planet that braking maneuver, in which of manufacturing techniques Global Surveyot, which slid give rise to the magnetic the spacecraft dips into the to work with the scuff.