From: Peiser Benny <[EMAIL PROTECTED]> To: cambridge-conference <[EMAIL PROTECTED]> Subject: CCNet, 17 January 2001 Date: Wed, 17 Jan 2001 12:49:04 -0000 CCNet 9/2001 - 17 January 2001 ------------------------------ "The project also aims to see if scientists can alter the orbit of a comet to protect the Earth from falling matter. The impact would alter the comet's orbit by a "just barely measurable" 62 to 620 miles (100 to 1,000 km), [Mike] A'Hearn said." --The New York Times, 17 January 2001 "My research has been one disaster after another. [...] You need to have one interesting idea every day. Just like James Bond has a license to kill, I had a license to depart from the normal path of a scientist." --Richard A. Muller, 16 January 2001 (1) NASA AIMS TO BLAST COMET TO STUDY SOLAR SYSTEM Oliver Morton <[EMAIL PROTECTED]> (2) ONE DISASTER AFTER ANOTHER Scientific American, 17 January 2001 (3) LUSTING AFTER A LANDING ON EROS Weired Magazine, 16 January 2001 (4) ICE CHANNELS ON MARS Harvey Leifert<[EMAIL PROTECTED]> (5) SYNCHRONOUS PLANETARY ORBITS FOUND IN NEW SOLAR SYSTEM UniSci, 16 January 2001 (6) DISASTER DIPLOMACY Ilan Kelman <[EMAIL PROTECTED]> (7) WHERE DID SOLAR-SYSTEM LIFE BEGIN? Oliver Morton <[EMAIL PROTECTED]> (8) WHERE DID SOLAR-SYSTEM LIFE BEGIN? Steve Drury <[EMAIL PROTECTED]> ============== (1) NASA AIMS TO BLAST COMET TO STUDY SOLAR SYSTEM >From Oliver Morton <[EMAIL PROTECTED]> Benny -- this is the first time I've seen Deep Impact talked of -- albeit in passing -- as having some implications for planetary defence. Maybe I just haven't been paying attention. oliver morton [EMAIL PROTECTED] NASA Aims to Blast Comet to Study Solar System http://www.nytimes.com/2001/01/17/science/science-space-chile-d.html January 17, 2001 By REUTERS SANTIAGO, Chile - NASA scientists aim to blast a comet with a copper projectile to learn about the formation of the solar system as part of a $270 million project funded by NASA, the head of the project said on Tuesday. The project, called Deep Impact and which will cause an explosion capable of destroying a small town, would be the first space mission to probe inside a comet, whose primitive core could reveal clues about evolution of the solar system. "All our studies of comets look only at the surface layer. Our theoretical models tell us the surface has changed, and only the interior has the original composition. So our main goal is to compare the interior with the surface," the project's director, Michael A'Hearn, told reporters. Scientists chose copper, Chile's No. 1 export, because it is less likely to interfere with the materials inside the crater. In January 2004, a rocket would launch from Cape Canaveral, Florida, a spacecraft that would orbit the sun. In July 2005 the spacecraft would separate from a battery-powered, copper projectile that would collide with the comet 24 hours later at a velocity of 6 miles (10 km) per second. It would produce a crater the width of a football field and up to 100 feet (30 meters) deep. The spacecraft would observe the composition of the crater's interior, while telescopes on Earth would monitor the impact. The project also aims to see if scientists can alter the orbit of a comet to protect the Earth from falling matter. The impact would alter the comet's orbit by a "just barely measurable" 62 to 620 miles (100 to 1,000 km), A'Hearn said. The project would blast the Comet Tempel 1, which was discovered in 1867 and is a little less than Earth's distance from the sun, he said. It was chosen because its size, rotation and trajectory favor the project and because the collision would be observable from Earth. In February, NASA will carry out a preliminary design review to see if the project can succeed. Copyright 2000 The New York Times Company ============== (2) ONE DISASTER AFTER ANOTHER >From Scientific American, 17 January 2001 http://www.sciam.com/2001/0201issue/0201profile.html The father of the idea that a sibling of the sun periodically wreaks havoc on Earth finds inspiration in catastrophes BERKELEY, CALIF.--I first meet Richard A. Muller during a record-breaking heat wave. The astrophysicist is on his way to get a refreshment. Bottles of his favorite cold dairy drink--mocha milk--are stacked in a nearby vending machine. Through the clear front, the scientist notices something out of place: a juice can trapped obliquely against the glass. "I'll get either two drinks or none," he predicts playfully, inserting his change and selecting the beverage he thinks is most likely to knock the can free. Muller is unconcerned (or perhaps oblivious) that this selection is vanilla, not the flavor he came for. His purchase grazes the target but fails to knock the bottle down. Gambles like this one typify the life of Richard Muller--although usually the stakes are higher. The restless researcher loves to prowl for new scientific territory to conquer. "You need to have one interesting idea every day," he says. His graduate research concerned particle physics, but his accomplishments range from inventing an improved technique for carbon dating to designing an experiment for measuring the cosmic background radiation left over from the big bang about 15 billion years ago. These and other accomplishments won Muller a MacArthur Fellowship in 1982, a year after these so-called genius awards began. It was a turning point. After that, Muller felt liberated to do "crazy things," as he puts it. "Just like James Bond has a license to kill, I had a license to depart from the normal path of a scientist." On the surface at least, he fits the stereotype of a scientist. He will head to the lab in the middle of the night when an idea strikes him. His cluttered office, which overlooks the Berkeley campus of the University of California, where he has been since he received his Ph.D. in particle physics here 32 years ago, could be a set from an absentminded-professor comedy. There's hardly enough floor space for a visitor amid filing cabinets and desks and cartons overflowing with journals and papers. His in-box groans under a two-foot-high stack. "My research has been one disaster after another," Muller puckishly offers. This well-rehearsed line is quite literally true. He did work on the big bang. He studied the violent supernova explosion preceding the creation of the sun. And then there's his Nemesis. "Nemesis" refers to a seemingly bizarre hypothesis concerning the evolution of life on Earth. Muller hatched it one day in 1983 when his mentor, Nobel laureate Louis Alvarez, enlisted the young physicist to debunk a research paper showing that Earth has sustained significant plant and animal extinctions at regular intervals--every 26 million years. Alvarez and his son, Walter, had recently advanced the theory that dinosaurs were the casualty of a Mount Everest-size comet that hit the planet 65 million years ago. At the time, the hypothesis was scoffed at; now it is generally accepted. Playing devil's advocate for Alvarez, Muller conjured up a scenario. Suppose, he suggested, the sun has a sibling around which it do-si-dos every 26 million years. And suppose that once each revolution the star swings through the Oort cloud, a calving ground for comets between four trillion and 10 trillion miles from us. Perhaps some of those icy balls, of which there are billions, would be knocked off-kilter and sent hurtling into Earth. At first the idea seemed preposterous, even to Muller himself. But neither Muller nor Alvarez could think of any reason why the theory couldn't be true. With a touch of whimsy, Muller dubbed the star Nemesis, after the Greek goddess who fends off human folly. "We worry that if the companion is not found," he stated in the scientific article introducing the theory, "this paper will be our nemesis." It seems counterintuitive that the solar system could be looping around an unknown star, but in fact most stars have partners: some 85 percent have some kind of companion. The only way to identify which, if any, of the catalogued stars is the sun's sibling requires measuring the distances to them. Muller says the elliptical orbit of Nemesis would get no farther than about 18 trillion miles from Earth, about three light-years away and three quarters the distance to the closest known star, Alpha Centauri. It could be a red dwarf star, which might be bright enough to be seen with a small telescope, or, less likely, a brown dwarf, which might not be visible at all. When he dreamed up the theory nearly two decades ago, Muller thought he would locate Nemesis in just a few years. Given its putative distance and brightness, it should be easy to find such a star through parallax measurements--seeing how it shifts against the more distant stellar background as Earth moves along in its orbit. But the search, short on funds for telescope time, languished and stalled. Muller says most astronomers think his theory was disproved, when in fact it is simply in limbo. It is no coincidence that so much of his career has been spent studying such tumultuous events. For centuries, scientists have predicated theories about Earth's evolution on the principles of uniformitarianism and gradualism, which posit that by and large the planet evolved slowly, relying on the same forces we see at work today, such as erosion and continental drift. Muller, however, believes infrequent, violent events are just as important--a doctrine some call catastrophism. Muller says neglect of catastrophic explanations gives him a strategic opportunity: "That's where the discoveries are." Most recently, Muller has begun delving into the ice ages. Geologists still have a hard time explaining why they come and go. Muller insists the answer is of much more than academic interest. Springing from his office chair, he heads to a blackboard in an adjoining room--he couldn't locate any chalk in his office--and sketches a graph of global temperature since the industrial revolution. Overall, global temperature has gone up about 1.5 degrees Fahrenheit in the past 120 years--and 15 to 20 degrees since glaciers receded 12,000 years ago. "Anything that can have an impact of 15 degrees is probably having an impact on the present climate," he reasons. Ice ages come and go at approximately 100,000-year intervals. The conventional explanation, refined and popularized by Serbian mathematician Milutin Milankovitch in the decades before World War II, involves subtle irregularities in Earth's motion. The theory mainly posits that the eccentricity, or out-of-roundness, of Earth's orbit varies the amount of sunlight bathing our planet. Painstaking reconstructions of Earth's past movements show that the planet's orbit around the sun goes from almost perfectly round to slightly oval and back in 100,000 years, matching the interval between ice ages. But there are problems. For instance, the modest change in orbital eccentricity does not make nearly enough difference in sunlight reaching Earth to produce ice ages. Another problem is that some ice ages appear to have begun before the orbital changes that supposedly caused them. Although adherents think that more research will explain such conflicts, Muller believes the textbook Milankovitch theory is hopelessly flawed. His own answer rests on a different aspect of Earth's orbit: Imagine the solar system is a vinyl record. Earth travels precisely on the record, called the ecliptic, only some of the time. At other times, the orbit is inclined a few degrees to the disk. Over a 100,000-year cycle, Earth's orbit begins in the ecliptic, rises out of it, then returns to where it started. This slow rocking, Muller proposes, is responsible for Earth's ice ages. He says the regions above and below the ecliptic are laden with cosmic dust, which cools the planet. Muller's inclination theory got a shot in the arm in 1995, when Kenneth Farley, a geochemist at the California Institute of Technology, published a paper on cosmic dust found in sea sediments. He began the research expecting to give Muller's theory a knockout punch but discovered that cosmic dust levels do indeed wax and wane in sync with the ice ages. But most researchers seem to echo the sentiment of Wallace Broecker, a geochemist at Columbia University, who thinks Muller is fooling himself. In 1996 Broecker brought a group of top-flight climate researchers together to hear Muller's theory. He says they found the presentation "riveting," but "they didn't buy it." "There's no mechanism attached to the idea," states Nicholas J. Shackleton, a marine geologist at the University of Cambridge and a leading proponent of the Milankovitch theory. He questions how small changes in interplanetary dust could result in effects as dramatic as the coming and going of ice ages. Muller responds that dust from space influences cloud cover on Earth and could have profound climatic implications. He says his theory, if viewed objectively, does just as well at explaining the facts as Milankovitch's. Referring to football, Muller calls himself a free safety of science, a generalist who scores intellectual touchdowns because he is unrestrained by questionable preconceived ideas. "Every once in a while there's a fumble" that no one notices, Muller says, "and I can grab that ball and run into the end zone." --DANIEL GROSSMAN DANIEL GROSSMAN is a freelance writer based in Watertown, Mass. Copyright 2001, Scientific American =========== (3) LUSTING AFTER A LANDING ON EROS >From Weired Magazine, 16 January 2001 http://www.wired.com/news/technology/0,1282,41119,00.html by Lisa Nadile Take these ingredients: A spinning rock about 21 miles in length and covered with small boulders and craters. An automobile-sized craft that weighs 1,775 pounds. No fuel. A blindfold. Johns Hopkins space jockeys. A dash of adventure. What do you have? Not the script to another bad space disaster movie, but an actual scientific endeavor that aims to land a vehicle on a asteroid. "You got the picture. We're winging it," said Dr. Robert Farquar, NEAR Shoemaker mission director at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. NEAR stands for Near Earth Asteroid Rendezvous. Shoemaker is for the late Eugene "Super Gene" Shoemaker, a world-renowned geologist at the U.S. Geological Survey in Flagstaff, Arizona, and a close friend of Farquar. The asteroid is named Asteroid 433 Eros, and the "rendezvous" originally meant to fly around the rock, take some pictures and then crash. The mission was to last a year, then on Feb. 12 come to a rather abrupt end. That mission has changed somewhat. Now they're actually trying to land the darn thing -- a challenge Farquar says has about a 1 percent chance of success. "It'll end up on the surface one way or another," Farquar said. "I like the description of landing on a moving aircraft carrier, if it's spinning and the deck is coming up at you." Admittedly the landing is a piloting exercise for the John Hopkins University based team. "This exercise in landing on small bodies like Eros is applicable. I can see asteroids used as temporary quarters for traveling larger distances," he said. "We'll slow the NEAR Shoemaker down and try the landing at about jogging speed." However, there is more to the landing than just derring-do. "This is the first time we've taken pictures this close of anything since the moon and a few small areas of Mars," said Dr. Clark Chapman, a NEAR imaging team member and a geologist for the Southwest Research Institute in San Antonio, Texas. The photos taken during the landing are expected to be 10 times better than those taken from orbit. "We want to find out what it's made of," he said. NEAR Shoemaker totes a range of scientific tools. A magnetometer to check for magnetic materials like those found in meteorites. An X-ray/Gamma-ray spectrometer for measuring silicon, magnesium, iron, uranium, thorium and potassium. A near-infrared spectrometer to map the mineral composition of the surface by measuring the spectrum of sunlight reflected by the asteroid. A multispectral camera and a laser rangefinder to measure the clog shoe-shaped EROS landforms and colors. And the craft has performed experiments to evaluate the density of Eros. "When we looked at the moon's lunar surface we saw a few scattered boulders but mostly the moon was covered with small craters, but EROS is covered with small boulders and hills, he said. "Asteroids are strange places from what little we know. Eventually we will mine and take samples and deal with what they can tell us," Dr. Chapman said. "With this kind of imaging, it's no different from taking a camera and going hiking, expect we're hiking into Wonderland. We didn't know what to expect." The NEAR Shoemaker doesn't have to land, but the activities of the space jockeys like Farquar is all gravy, Chapman said. The plans for landing were a surprise to many. "I thought about doing this early on, but I didn't have the nerve to say anything," Farquar said. "He is mischievous and intriguing. NASA is extremely risk-adverse ... and a bit straitlaced. Farquar is a breath of fresh air," Chapman said. Launched from Cape Canveral Air Station in 1996, NEAR's arrival at Eros on Valentine's Day of last year was no accident. Eros is 1.3 astronomical units from the Sun, where Earth is 1 astronomical unit. It is classified as a near-Earth asteroid, which means it travels within 121 million miles of the Sun. Scientists theorize that these types of asteroids are from the main belt between Mars and Jupiter. The NEAR Shoemaker adventure is not only about the adventurers who man our space programs, but about trying the impossible. Farquar, Chapman and the rest of the NEAR Shoemaker team engage in friendly competition with their NASA counterpart, the Jet Propulsion Laboratory. But they all want the same thing. Repeat after me: To boldly go ... Copyright © 2001 Wired Digital Inc., a Lycos Network site. All rights reserved. =========== (4) ICE CHANNELS ON MARS >From Harvey Leifert<[EMAIL PROTECTED]> American Geophysical Union January 16, 2001 AGU RELEASE NO. 01-2 For Immediate Release Contact: Harvey Leifert (202) 777-7507 [EMAIL PROTECTED] Martian ice streams, not floods, may have shaped channels WASHINGTON - Some channels visible on the surface of Mars may have been gouged by ice, rather than by catastrophic flooding, as is generally believed. That is the view of Dr. Baerbel K. Lucchitta of the U.S. Geological Survey in Flagstaff, Arizona, who compared the Martian features with strikingly similar ones on the Antarctic sea floor. Her findings are reported in the February 1 issue of Geophysical Research Letters, a publication of the American Geophysical Union. Outflow channels on Mars may be tens of kilometers [miles] wide and hundreds of kilometers [miles] long, as are some that Lucchitta studied in Antarctica. Ice flows in streams within Antarctica's ice sheets before merging with ice shelves in the surrounding ocean; the ones she studied flow from West Antarctica into the Ross and Ronne Ice Shelves. The martian channels arise suddenly from chaotic terrains or fractures and terminate in the northern plains, where there may once have been an ocean. Both the Antarctic ice streams and some martian channels are based below sea level, which on Mars is defined as the average surface elevation of the hypothetical ancient northern plains ocean. The Antarctic channels were mapped using recently available sonar imagery. Lucchitta demonstrates that martian channels, especially one known as Kasei Valles, display similar characteristics to those of Antarctic channels known to have been carved by ice streams. She compares the Rutford Ice Stream at its confluence with the Ronne Ice Shelf, where it diverges around an ice rise, formed of more stable ice than the adjacent flow, with Ares Vallis. The latter diverges around an island and displays similar curved flow lines where it enters the hypothetical ocean. The configuration of these two streams is identical, she writes. Lucchitta infers that Ares Vallis was filled by material that had the characteristics of flowing ice that entered an ice covered body of water. She believes that dust covered ice may persist in Ares Vallis or that rocky material left an expression of the flow forms after the ice evaporated. "The observations strongly support the notion that an ocean once existed in the northern plains of Mars," she says. Another similarity between Antarctica and Mars noted in the study is that some streams and channels rise in altitude in the downstream direction. On Earth, uphill flow at the base of ice is common, because the surface gradient drives the ice, whereas water does not flow uphill for extended distances. There are differences between Antarctica and Mars regarding the origin of ice in ice streams. On Earth, the streams flow from ice sheets, while on Mars, it derived from fluids erupting from below the surface. Also, on Earth, the ice flows between ice walls, while on Mars it flowed between rock walls, but the width to depth ratio on Mars is more like that of ice streams than of mountain glaciers on Earth, Lucchitta notes. The study was funded by NASA's Planetary Geology and Geophysics Program. ********** Notes for journalists only: 1. A copy of the paper, Baerbel K. Lucchitta, "Antarctic Ice Streams and Outflow Channels on Mars," (four pages) may be obtained by fax or mail. Send your request to Harvey Leifert: <[EMAIL PROTECTED]>. The paper will be published in Geophysical Research Letters (GRL), Vol. 28, no. 3 (February 1, 2001), pages 403-406. 2. Pronunciation of author's name: BEAR-bel Lu-KEE-ta 3. Images: Three figures accompany this paper. They may be obtained from the AGU web site at the following URL: http://www.agu.org/grl/images/vol28/ant_chan.html [Figure 3 will appear on the cover of GRL.] 4. This press release and the Lucchitta paper are not embargoed. 5. Dr. Lucchitta may be contacted at her office. Phone: +1 (520) 556-7176; email <[EMAIL PROTECTED]>. ============= (5) SYNCHRONOUS PLANETARY ORBITS FOUND IN NEW SOLAR SYSTEM >From UniSci, 16 January 2001 http://unisci.com/stories/20011/0116011.htm Johannes Kepler succeeded in establishing a formula for relating a planet's orbital period to its mean distance from the sun, but he failed in his ardent attempt to discern a pattern in the spacings or periods among the planets. Such a pattern, enforced by resonant gravity effects, was subsequently observed in the commensurate periods of some of Jupiter's moons. Now the reality of synchronous planetary orbits has turned up in a solar system unknown to Kepler -- or to anyone else -- until recently. Geoffrey Marcy (UC Berkeley) and his associates, discoverers of tens of extrasolar planets, now report that the star Gliese 876, 15 light years from Earth, is orbited by one planet every 60 days and by a second every 30 days. (The presence of the planets around the star and their orbital properties are deduced from the subtle wobble of the star's position as it is tugged by its satellites.) The almost exact 2:1 (octave) ratio in the orbital periods should help theorists model the formation of planetary systems. Marcy, speaking at last week's meeting of the American Astronomical Society (AAS) in San Diego, also reported a second two-planet extrasolar system no less novel. The star HD168443, 123 light years from Earth, is circled every 58 days by one heavy planet (7.7 Jupiter masses) at a distance of only 0.3 astronomical units (1 AU is the distance from Earth to sun) and by another every 4.8 years. The second planet's mass, estimated to be at least 17 Jupiter masses, is the most massive exoplanet ever found, and calls into question the notion that planets could not reach much above 13 Jupiter masses without igniting as stars. (Editor's Note: This story reprints, with only minor editing, an item from PHYSICS NEWS UPDATE, the American Institute of Physics Bulletin of Physics News Number 520 January 12, 2001 by Phillip F. Schewe, James Riordon, and Ben Stein.) Copyright © 1995-2001 UniSci. All rights reserved ============= (6) DISASTER DIPLOMACY >From Ilan Kelman <[EMAIL PROTECTED]> Disaster Diplomacy (edited by Ilan Kelman and Theo Koukis) in the Cambridge Review of International Affairs vol. XIV, no. 1, Autumn-Winter 2000 "Greek-Turkish Rapprochement: The Impact of 'Disaster Diplomacy'?", by James Ker-Lindsay: "To claim that the earthquakes brought about rapprochement is both factually wrong, and indeed weakens the basis for the process." "Climate-Related Disaster Diplomacy: A US-Cuban Case Study," by Michael H. Glantz "A broad-ranging rapprochement is not likely to result from a specific response to a climate-related problem." "Drought Emergency, Yes...Drought Disaster, No: Southern Africa 1991-93," by Ailsa Holloway "While diplomatic dividends can indeed flow from disaster relief efforts, in this instance, joint cooperation was only possible once potential military, economic, and other forms of regional confrontation had been controlled." "Disaster: Agent of Diplomacy or Change in International Affairs?" by Louise K. Comfort "Disaster--or threat of disaster--provides opportunities for enhancing collaboration among states, but the properties and mechanisms for adaptation must either exist or be developed for effective results." Plus, from Vincent T. Gawronski and Richard S. Olson: "'Normal' Versus 'Special' Time Corruption: An Exploration of Mexican Attitudes." Copies of this issue are available for GBP10 plus postage from: Cambridge Review of International Affairs Centre of International Studies Fitzwilliam House 32 Trumpington Street Cambridge CB2 1QY UNITED KINGDOM Telephone: + 44 (0) 1223 741311 Fax: + 44 (0) 1223 741313 E-mail: [EMAIL PROTECTED] ============================ * LETTERS TO THE MODERATOR * ============================ (7) WHERE DID SOLAR-SYSTEM LIFE BEGIN? >From Oliver Morton <[EMAIL PROTECTED]> Re: EARTH IS THE MOST LIKELY PLACE FOR LIFE'S ORIGIN IN OUR SOLAR SYSTEM From Steve Drury <[EMAIL PROTECTED]> In their paper "Refugia from asteroid impacts on early Mars and the early Earth" JGR v103, E12, pp28, 529-28,544 Norm Sleep and Kevin Zahnle offer two reasons to prefer Mars as a solar-system origin of life, both intriguing but not compelling. If you think life is very likely whenever there are organics on a planet and the temperature allows liquid water, then Mars meets the criteria in a continuous way earlier than the earth because the moon-causing impact effectively resets the earth's clock. Sleep and Zahnle also point out that ocean sized bodies of water might count against the earth, since large impacts can boil the earth's oceans, causing a steam atmosphere that persists for thousands of years. This steam atmosphere allows the 100 deg C isotherm to penetrate reasonably deep into the subsurface all around the planet. On drier Mars -- if Mars was drier -- the global effects of these really large impacts are less dramatic. This raises the intriguing logical possibility that the conditions for the origin of life need not be the same as the conditions for its persistence. As to the amount of transfer between planets, isn't this a red herring? The important thing is that there is significant transfer, not whether the net flux is in the opposite direction. While it is true that if there had been life on earth and mars at the same time, more earthlife might be expected to have made the journey out than Marslife make the journey in. But if there was life on mars and not on earth at a given time, surely the fact that Mars to earth transfer was rarer than earth to Mars transfer is irrelevant. As far as I can see, if life originated on a planet in the solar system and transfer from planet to planet is indeed possible, then the origin could have been Venus, earth, Mars or the unnamed Mars-sized earth-impactor that contributed to the moon. It's not clear to me that we can say anything more than that with certainty, and we have to realise that two of the four possible sources are now unrecoverable. Incidentally, could I make another plea for my neologism "transpermia" to describe this sort of transfer between neighbouring planets, as opposed to the more cosmic "panspermia". In cases where one is being precise about the origin and the method, transpermia seems preferable. best, oliver =============== (8) WHERE DID SOLAR-SYSTEM LIFE BEGIN? >From Steve Drury <[EMAIL PROTECTED]> Dear Oliver/Benny Like I said, I don't wish to make a meal of this, because it is all special pleading in the absence of evidence. When we are dealing with the period from 4500-4000 Ma on Earth, all we have to go on are a couple of dozen 30 micrometre zircon grains - see last issue of Nature, which is an excellent example of milking data to the limit! For Mars, a great deal hangs on the analyses of the Martian atmosphere from Viking - very imprecise, but clung to in claiming some rare meteorites are Martian in origin, with no clear justification of why such deeply excavated objects should carry any atmosphere at all. All we know for sure is that these objects are geochemically quite evolved - i.e. from a body able to fractionate internally. That could be Venus, Earth, Mars, Io and any other body known to resurface itself periodically or continually You mention the notion that Mars is more likely than Earth to have developed life early, because it was not involved in the Moon-forming event. We simply do not know whether or not it was involved in such energetic processes early on, for its surface is young, due to its cover of wind- and to a lesser extent water-transported sediments. All we have to go on is that the inclination of its rotational axis is similar to that of the Earth - possibly due to large-impact perturbation. Large impacts can boil oceans, but converting all liquid water to vapour means distribution of impact energy from a point to the whole planet - not so easy as most is lost either to seismicity of radiated away above site of impact. The issue of sterilizing the subsurface is probably not on, simply because of the very low thermal conductivity of rocks - you can stand on the crust of a still-active lava flow with magma at 1200 C only 10 or so metres beneath the surface. Hyperthermophiles are today found to depths of 2 km or more. Besides that, Mars has a greater gravitational cross section than the Moon or the cratered moons of the giant planets, and is almost as likely as Earth to have been hit by bodies able to vaporize surface water in the Hadean. My last word on the panspermia notion is the old saw that it merely shifts origins conveniently somewhere else. It is simply not useful to say that wherever there are CHON compounds and liquid water life will spring up. The pace of assembly of universal building blocks to hypercomplex, self-replicating chemical systems is simply unknown, even though a number of possible pathways are beginning to emerge from simple experimental systems. What we do know is that the transition from naked genetic material in prokaryotes to its encapsulation in eukaryote nuclei and organelles, probably by some kind of endosymbiosis and genetic exchange mechanisms, took around 2 billion years under highly favourable conditions. Personally, I would be surprised if assembly of simple prokaryotic cells from universally available amino acids etc. (chemically and thermodynamically a whole lot more difficult) could be shown to have taken less than a few hundred Ma. But I can be smug in the certainty that no-one will find out in my lifetime! Incidentally, Hoyle's idea of flu viruses being delivered by interplanetary dust particles needs to be viewed in the context of two recent revivals of Triassic bacteria from fluid inclusions in rock salt. Every time I go out on a frosty night I worry now about what is being released by salt on the roads! Steve Drury -------------------------------------------------------------------- THE CAMBRIDGE-CONFERENCE NETWORK (CCNet) -------------------------------------------------------------------- The CCNet is a scholarly electronic network. To subscribe/unsubscribe, please contact the moderator Benny J Peiser <[EMAIL PROTECTED]>. Information circulated on this network is for scholarly and educational use only. The attached information may not be copied or reproduced for any other purposes without prior permission of the copyright holders. 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