MARSBUGS: The Electronic Astrobiology Newsletter Volume 8, Number 48, 17 December 2001. Editors: Dr. David J. Thomas, Science Division, Lyon College, Batesville, AR 72503-2317, USA. dthomas@lyon.edu Dr. Julian A. Hiscox, School of Animal and Microbial Sciences, University of Reading, Reading, RG6 6AJ, United Kingdom. J.A.Hiscox@reading.ac.uk Marsbugs is published on a weekly to monthly basis as warranted by the number of articles and announcements. Copyright of this compilation exists with the editors, except for specific articles, in which instance copyright exists with the author/authors. While we cannot copyright our mailing list, our readers would appreciate it if others would not send unsolicited e-mail using the Marsbugs mailing list. The editors do not condone "spamming" of our subscribers. Persons who have information that may be of interest to subscribers of Marsbugs should send that information to the editors. E-mail subscriptions are free, and may be obtained by contacting either of the editors. Article contributions are welcome, and should be submitted to either of the two editors. Contributions should include a short biographical statement about the author(s) along with the author(s)' correspondence address. Subscribers are advised to make appropriate inquiries before joining societies, ordering goods etc. Back issues and Adobe Acrobat PDF files suitable for printing may be obtained from the official Marsbugs web page at http://welcome.to/marsbugs. The purpose of this newsletter is to provide a channel of information for scientists, educators and other persons interested in exobiology and related fields. This newsletter is not intended to replace peer- reviewed journals, but to supplement them. We, the editors, envision Marsbugs as a medium in which people can informally present ideas for investigation, questions about exobiology, and announcements of upcoming events. Astrobiology is still a relatively young field, and new ideas may come from the most unexpected places. Subjects may include, but are not limited to: exobiology and astrobiology (life on other planets), the search for extraterrestrial intelligence (SETI), ecopoeisis and terraformation, Earth from space, the biology of terrestrial extreme environments, planetary biology, primordial evolution, space physiology, biological life support systems, and human habitation of space and other planets. _____________________________________________________________________ CONTENTS 1) METHANE EXPLOSION WARMED THE PREHISTORIC EARTH, POSSIBLE AGAIN NASA/GSFC release 01-117 2) CASSINI-HUYGENS: SEVEN YEARS TO SATURN NASA/JPL release 3) 2002 SYMPOSIUM: MARS ON EARTH, LIFE ON MARS Mars Society UK release 4) SETI SOCIAL SCIENCE: WHAT MAKES A GOOD ONLINE SURVEY? By Douglas Vakoch 5) WHERE TO LAND ON MARS? IT'S NOT AS EASY AS IT LOOKS NASA/JPL release 6) SEEKING CONTACT: CARL SAGAN CENTER TO FOCUS ON LIFE IN THE UNIVERSE By Leonard David 7) GEOPHYSICIST STUDIES LIFE IN THE EARLY SOLAR SYSTEM By Etienne Benson 8) NEW ADDITIONS TO THE ASTROBIOLOGY INDEX By David J. Thomas 9) CASSINI WEEKLY SIGNIFICANT EVENTS NASA/JPL release 10) STARDUST STATUS REPORT NASA/JPL release _____________________________________________________________________ METHANE EXPLOSION WARMED THE PREHISTORIC EARTH, POSSIBLE AGAIN NASA/GSFC release 01-117 10 December 2001 A tremendous release of methane gas frozen beneath the sea floor heated the Earth by up to 13 degrees Fahrenheit (7 degrees Celsius) 55 million years ago, a new NASA study confirms. NASA scientists used data from a computer simulation of the paleo-climate to better understand the role of methane in climate change. While most greenhouse gas studies focus on carbon dioxide, methane is 20 times more potent as a heat-trapping gas in the atmosphere. In the last 200 years, atmospheric methane has more than doubled due to decomposing organic materials in wetlands and swamps and human aided emissions from gas pipelines, coal mining, increases in irrigation and livestock flatulence. However, there is another source of methane, formed from decomposing organic matter in ocean sediments, frozen in deposits under the seabed. "We understand that other greenhouse gases apart from carbon dioxide are important for climate change today," said Gavin Schmidt, the lead author of the study and a researcher at NASA's Goddard Institute for Space Studies in New York, NY and Columbia University's Center for Climate Systems Research. "This work should help quantify how important they have been in the past, and help estimate their effects in the future." The study [was] presented on December 12, 2001, at the American Geophysical Union (AGU) Fall Meeting in San Francisco, CA. Generally, cold temperatures and high pressure keep methane stable beneath the ocean floor, however, that might not always have been the case. A period of global warming, called the Late Paleocene Thermal Maximum (LPTM), occurred around 55 million years ago and lasted about 100,000 years. Current theory has linked this to a vast release of frozen methane from beneath the sea floor, which led to the earth warming as a result of increased greenhouse gases in the atmosphere. A movement of continental plates, like the Indian subcontinent, may have initiated a release that led to the LPTM, Schmidt said. We know today that when the Indian subcontinent moved into the Eurasian continent, the Himalayas began forming. This uplift of tectonic plates would have decreased pressure in the sea floor, and may have caused the large methane release. Once the atmosphere and oceans began to warm, Schmidt added, it is possible that more methane thawed and bubbled out. Some scientists speculate current global heating could eventually lead to a similar scenario in the future if the oceans warm substantially. When methane (CH4) enters the atmosphere, it reacts with molecules [composed] of oxygen (O) and hydrogen (H), called [hydroxyl] radicals (·OH). The ·OH combine with methane and break it up, creating carbon dioxide (CO2) and water vapor (H2O), both of which are greenhouse gases. Scientists previously assumed that all of the released methane would be converted to CO2 and water after about a decade. If that happened, the rise in CO2 would have been the biggest player in warming the planet. But when scientists tried to find evidence of increased CO2 levels to explain the rapid warming during the LPTM, none could be found. The models used in the new study show that when you greatly increase methane amounts, the ·OH quickly gets used up, and the extra methane lingers for hundreds of years, producing enough global warming to explain the LTPM climate. "Ten years of methane is a blip, but hundreds of years of atmospheric methane is enough to warm up the atmosphere, melt the ice in the oceans, and change the whole climate system," Schmidt said. "So we may have solved a conundrum." Schmidt said [that] the study should help in understanding the role methane plays in current greenhouse warming. "If you want to think about reducing future climate change, you also have to be aware of greenhouse gases other than carbon dioxide, like methane and chlorofluorocarbons," said Schmidt. "It gives a more rounded view, and in the short-term, it may end up being more cost- efficient to reduce methane in the atmosphere than it is to reduce carbon dioxide." For more information please see http://www.gsfc.nasa.gov/topstory/20011212methane.html. _____________________________________________________________________ CASSINI-HUYGENS: SEVEN YEARS TO SATURN NASA/JPL release 10 December 2001 As if going to Saturn wasn't hard enough, deciding what science to collect once in orbit around the giant planet is a logistic maze. Launched in 1997, the international mission Cassini-Huygens will take almost seven years to reach the planet famed for those amazing rings that puzzled generations of astronomers. To save fuel and to travel the huge distance, more than 3 billion kilometers so far, the spacecraft used a technique called gravity assist. It looped around Venus twice, then flew past Earth and finally around Jupiter. The slingshot boost from these passes will deliver the Cassini orbiter and its probe, Huygens, to Saturn in July 2004. The probe will later descend to Titan, the biggest of some 30 known moons orbiting Saturn. The Huygens probe will provide information on Titan, which has an atmosphere that extends about 1,000 kilometers (620 miles) from the surface. Because of its distance from the Sun, its surface is frozen and its temperatures are extremely low. Compared to Earth, Titan receives only one percent of the Sun's light. Choosing what data to collect with the spacecraft's many instruments once at Saturn is keeping scientists busy these days, as they are planning a minute-by-minute timetable for the four-year mission. The challenge is caused by the abundance of interesting science targets along the planned 74 orbits around Saturn, and the wealth of instruments onboard the spacecraft. "There is a lot of intriguing science with Titan, the most Earth-like world out there, and we want to know a lot more about Saturn," says Dr. Kevin Baines, a planetary scientist at JPL involved with the science timetable. "The rings are sitting there, shining away. They are mysterious and we are going to look at those and also the icy satellites." Logistic issues complicate the planning task One matter is downloading the information collected by the data recorder on board. Once it is full, the spacecraft must turn toward Earth and begin downloading the data. Because of the great distance, the signal takes about an hour and 15 minutes to reach the Deep Space Network's antennas. Downloading the data takes up to 9 hours. When Cassini is collecting data, scientists have to make hard choices on which instrument to use. In order to save money, Cassini's instruments are all fastened in fixed positions and cannot be pointed independently of another. "We have all these mutually exclusive desires," explains Baines. "We have different targets and when we get to a particular target there are a lot of different things we want to do. All the scientists involved must collaborate with each other." Eager to decode the many mysteries of Saturn and its moons, scientists are painstakingly examining each of the 74 planned orbits around the planet, trying to include as many unique and relevant observations as possible, without compromising each other's instruments and goals. The complicating factor is that of the 265 scientists involved with the mission, only 125 live in the U.S. This translates in teleconferences across 12 time zones, with scientists in Hawaii getting up early while their colleagues in Europe are putting their kids to bed. Through tons of emails, web charts and conference calls, scientists from 16 countries have 30 months to come up with an integrated time chart that will provide the best plan to gather as much information as possible about the sixth planet from the Sun, the second largest in our solar system. More information on this article is available at http://www.jpl.nasa.gov/solar_system/features/saturn.html. _____________________________________________________________________ 2002 SYMPOSIUM: MARS ON EARTH, LIFE ON MARS Mars Society UK release 10 December 2001 On Saturday 19th January 2002, the Mars Society UK will be hosting a 1-day symposium entitled "Mars on Earth: Life on Mars" and will present Society members, space professionals and members of the general public to find out more about Mars, our attempts to explore Mars both with robotic and human missions, and the potential for life on Mars. The symposium is to be held at the National Hockey Stadium Conference Centre, a prestigious facility centrally located in Milton Keynes, England, with convenient road, rail and air links (London Luton airport). Registration for the event starts at just £10.00 (17.00 Euros), and accommodation can be arranged at a number of hotels all within easy walking distance of the symposium venue. Speakers for the event include: * Professor Colin Pillinger, Principal Investigator, Beagle 2. * Doctor Robert Zubrin, author of "The Case for Mars", architect of the Mars Direct humans-to-Mars mission profile and President of the Mars Society. * Doctor Charles Frankel, European Space Agency, and member of the Flashline Mars Arctic Research Station project. * Martyn Fogg, terraforming expert. Further speakers to be announced shortly. Attending the event The symposium is open to any and all who have an interest in the exploration of Mars. On-the-door registrations will be available (depending on numbers), but to avoid disappointment, use our registration form to book your place at the symposium in advance, and we'll even ensure you have a hotel room reserved for you as well, should you require it! More information is available at http://www.marssociety.org.uk/sections.php?op=viewarticle&artid=61. _____________________________________________________________________ SETI SOCIAL SCIENCE: WHAT MAKES A GOOD ONLINE SURVEY? By Douglas Vakoch From Space.com 10 December 2001 There's a reason that Internet polls often bear disclaimers, noting that they are not to be taken as scientific studies. In this article, I'll explain some of the reasons for such cautionary labeling, using our recent SETI Institute/SPACE.com survey on attitudes toward extraterrestrial life to illustrate the points. Though it would be tempting to dive right into the results of our survey, it's important to be clear about some of the challenges facing the social scientist who would use the Internet to conduct surveys. Although we can describe many of the steps that social scientists go through in their work, it's critical to recognize that the conclusions we can draw based on data collected over the Internet are unlikely to stand up to the rigorous scrutiny of conscientious researchers who rely on other ways to gather data, such as face-to- face interviews... ...But even in the best scenarios, Internet surveys can provide very skewed impressions of people's attitudes--in part, simply because it's hard to generalize from Internet users to the general populace. If we discover that visitors to SPACE.com are overwhelmingly positive about the prospects of making contact with ET, it's hard to know how closely that corresponds to the views of people who 1) don't use the Internet, and 2) don't have special interests in space activities. While we can get around some of these problems by posting surveys at multiple sites, in the end, the problem of unrepresentative sampling is only minimized, and never eliminated. Get the full story at http://www.space.com/searchforlife/setisurvey_follow_011210.html. _____________________________________________________________________ WHERE TO LAND ON MARS? IT'S NOT AS EASY AS IT LOOKS NASA/JPL release 12 December 2001 Of all the places to land on Mars, where in the world should twin rovers go? This question has been on the front burner of discussion with Mars scientists who have the arduous task of selecting a site where it is safe to land and yet is rich in rocks, layered terrain and other geologic features that will beckon a host of scientific inquiries and discoveries for the Mars Exploration Rover mission scheduled to launch in 2003. Mars scientists all agree on one thing: the search is on for landing sites where water was once present on the surface of Mars. The science instruments on the rovers are all geared toward understaning if the planet was warmer and wetter in the past, and for how long. Answering these questions is important to understanding how Earth and Mars have differed in climate and geology throughout their development. Since water is key to living organisms, they also address the potential that life may have developed on Mars long ago. Leading the charge As more than a hundred scientists gathered in study teams and burned the midnight oil over six months of intense calculations, Dr. Matt Golombek has overseen a lively but collegial process that has taken place. As JPL's Mars Exploration Landing Site scientist, he looks after the selection process, carefully weighing the choices at hand. Scientists and engineers working with him have painstakingly narrowed the best places to land from 185 to four, and are now focused on selecting the final two. "We want to go to sites with terrains that will challenge our minds but not the safety of the rovers," said Golombek, who was also project scientist on the Mars Pathfinder mission and selected its landing site. Plainly speaking, he said, the science group has ruled out areas that are flat and safe but boring, and have homed in on sites that appear flat, safe and interesting. The site selection process is a convergence between engineers who know the capabilities and limitations of the machines they are sending to Mars, and scientists who can determine the scientific worth of the areas accessible to the spacecraft. Everyone, he said, is working toward that goal. Narrowing the options Major constraints dramatically narrowed down the territory on Mars that could even be considered. The candidate regions chosen, each comprising an area about the size of Southern California, exist below a certain elevation to provide enough atmosphere for the lander's parachute to descend properly. The sites also sit in a largely equatorial latitudinal band where enough sunlight shines to keep the solar-powered rovers supplied with electricity. Areas dominated by steep slopes, such as ravines or crater walls, are ruled out as hazardous to the lander and rover. Reducing the risk to the airbags Next to be eliminated were areas with large rocks. A rock larger than about one-half meter high, or knee-high to most people, is too tall for safety reasons. If the landing airbag system bounced hard on a rock that size, the rock might protrude high enough inside the airbags to damage the lander. Shorter boulders are considered acceptable, because even in the event of a direct bounce on top of one, the rock would not be tall enough to impinge on the lander inside. But using even the highest-resolution images available to search for sites dominated by right-size rocks, said Golombek, "you can't guarantee there won't be bigger rocks. You can't eliminate them." With vigilant study and deduction, however, "you can try to make smaller the probability of landing on one." Beware of stealthy terrain and "foo-foo dust" Laser altimeters will gauge the lander's altitude during descent in order to fire the solid rockets and deploy the parachutes and airbags at the right time. For those measurements to be made, the landers must be targeted to areas where the altimeter's radar will bounce back from the surface. Ruled out as landing sites are so-called "stealth regions". "Stealth regions" are locales on Mars where the radar penetrates the surface but doesn't bounce back--a characteristic these regions share with the military's radar-avoiding stealth technology. In the case of Stealth fighters and bombers, the aircraft surfaces are made of a high-tech, radar-absorbing material. In the case of Mars' "stealth regions," however, the answer isn't known, said Golombek. They may be covered with a meter or more of "foo-foo dust," a Dr. Seuss-like term that Golombek uses to describe possibly fluffy accumulations of Mars' fine iron-oxide dust particles that can pile up in drifts like red snow. In addition, "sending a solar-powered spacecraft to a dusty spot isn't a good idea. The stuff gets on the solar panels and reduces the power, gets stuck in the wheels and gears and generally gunks up the works" Golombek said. Rocks: too much of a good thing? Sites with too many rocks of any size are not desirable either, because a densely populated rock field can create a treacherous obstacle course for a rover. "Too many rocks inhibit mobility, but then again, you're going there to look at the rocks," said Golombek, pointing out another area where safety and scientific appeal must compromise. The site evaluation process started in September 2000 when Golombek and fellow scientist Tim Parker (also at JPL) identified nearly 200 possible landing sites that met the basic engineering constraints. Subsequent work and meetings have reduced that to four prime candidates and two backups. By May of 2002, a region measuring 600 by 900 kilometers will be selected--one for each rover. At that time, targeting data will be hardwired into the launch vehicles that will carry each rover. After launch, the two spacecraft will be more finely targeted during their cruises to Mars based on detailed navigation measurements taken on the way. At that time, the final landing boundary will be narrowed to a football-shaped ellipse of about 100 to 200 kilometers long by 20 kilometers wide. Mars Global Surveyor, an orbiter currently at Mars, has provided global elevation data through its laser altimeter, surface temperature and mineralogical readings from the thermal emission spectrometer, and images from the camera. New data collected by these instruments will be used to better characterize the sites in coming months. In addition, the recently arrived 2001 Mars Odyssey orbiter will start taking routine scientific data in early 2002, which will also be used in determining the final two sites selected. The four finalists and their runners-up Hematite "Hematite is a special place. It's one of three sites on Mars with detectable mineral signatures for coarse grained hematite." This type of hematite generally forms in water, so "finding hematite is like finding a sign that says 'Water was here!'" Not only does it rank high in scientific interest; Hematite measures high on the safety scale as well. Of the four sites, Golombek said, Hematite is very unique: "it's one of the smoothest, flattest, safest place in the equatorial region. All the other sites have good things about them and not-so-good things about them." Melas The Melas region is a canyon with 10-kilometer high walls (6 miles high) that "make the Grand Canyon look insignificant," said Golombek. "There is a area at its very center that has interior deposits that look like some type of sedimentary rock. Did these rocks form in water, was there a lake there? Were the layers deposited by water? Are they due to wind erosion or some other process? It's a prime place to address very important questions." Attractive though it is, said Golombek, Melas is surrounded by sand dunes. A bullseye in targeting would put the lander in fascinating terrain, but anything short of that could be disappointing. Gusev Crater "Gusev is perhaps the classic crater that looks like it was a crater lake," said Golombek. "For all the world, it looks like a crater that filled with water, which at some point breached the crater wall and the water escaped. If this occurred, the crater should be filled with sediments deposited in the lake." And if the sediments are there, they were laid down in watery solutions that will provide valuable clues in the search for water's past on Mars. The original landing ellipse considered for Gusev was found to contain some rough- looking terrain in Mars Global Surveyor data, so the ellipse was moved to gentler terrain slightly to the west. Athabasca Valles Finally, there's Athabasca Valles in the Elysium Planitia, or the "Plains of Elysium." "It is one of the youngest outflow channels on Mars," said Golombek. "It's hundreds of kilometers long with a catastrophic outflow channel, kind of like Ares Valles where Pathfinder landed. Geologically, it's very young, just tens to hundreds of millions of years old." The channel has been worn by water and has young volcanics as well, making it a prime location to look for hydrothermal deposits. Runners-Up Two backup sites wait in the wings in case there are problems found with the other sites: Isidis Planitia and Eos Chasma. The former sits close to some of the oldest material exposed on Mars, near the rim of a giant impact basin. The area is expected to be rich in very old rocks and so may provide clues to the early environment and whether it was watery or not. Telecommunications constraints Telecommunications constraints will bear on the selection of the final two sites. The two rovers will communicate via the same Deep Space Network and Mars orbiter spacecraft antennas, so the rovers must be separated by at least 36 degrees in latitude so there will be no telecommunications overlap between the two. If Hematite is chosen as one of the sites, it is located far enough away from the other sites that there would be no overlap, said Golombek. Choosing the right targets In April 2002, the third landing site workshop will meet in Pasadena to share any new scientific information gained about the top sites, and to discuss and evaluate the safety of the sites with mission engineers. From the discussions, two sites will be selected for landing the two Mars Exploration Rover spacecraft. A little help from orbiter friends "This is a unique period where we have orbital missions that can help us make the selection," he said. Mars Global Surveyor's continuing presence at Mars, now coupled with Mars Odyssey, provides unprecedented tools to gather targeted information down to 3-meter resolution--about the length of a small sedan--to help scientists make the landing site selection. Golombek compares today's comparative wealth of detailed data with the relative paucity of information he had in selecting Pathfinder's landing site in the mid-1990s. Studying images from the 1970s-era Viking mission, "we had a hundred meter resolution for the Pathfinder landing site. That's about the size of a football field. Now, we're directing the Mars orbiter camera on Surveyor to get pictures of landing sites at 3-meters resolution. Our data sets for Mars are so new and growing so quickly. It's a very dynamic, exciting time for Mars exploration." Suitable for human landing? Though no human exploration missions are planned for Mars yet, Golombek says the landing site selections could be driven by different constraints. "For future astronauts, water would be a prime resource," he said, noting that the hydrogen and oxygen in water could be a source for rocket fuel for a return trip to Earth. "There could be a completely different suite of constraints that could take you to completely different sites than we're considering right now," he said. More information on this article is available at http://mars.jpl.nasa.gov/spotlight/merlanding01.html. _____________________________________________________________________ SEEKING CONTACT: CARL SAGAN CENTER TO FOCUS ON LIFE IN THE UNIVERSE By Leonard David From Space.com 13 December 2001 Cutting-edge studies to help define how crowded the Universe might be with life are to be undertaken at new research facilities, named after a pioneer in the field: Carl E. Sagan. As currently envisioned, the Carl Sagan Center for the Study of Life in the Cosmos will consist of a trio of high-tech laboratories, with the potential to add a fourth at a later date. In addition, a public gallery exhibition area and 500-seat auditorium are also part of the center. The center is to be built on some seven acres of land in the planned NASA Research Park at Moffett Field, California, neighboring the space agency's Ames Research Center. Get the full story at http://www.space.com/searchforlife/sagan_seti_011213.html. _____________________________________________________________________ GEOPHYSICIST STUDIES LIFE IN THE EARLY SOLAR SYSTEM By Etienne Benson Stanford University release 14 December 2001 Between the cataclysmic impact that created the Moon around 4.5 billion years ago and the first evidence of life 3.8 billion years ago, there may have been long periods during which life repeatedly spread across the globe, only to be nearly annihilated by the impact of large asteroids. The early Earth, in other words, may have been an interrupted Eden--a planet where life repeatedly evolved and diversified, only to be sent back to square one by asteroids 10 or 20 times wider than the one that hastened the dinosaurs' demise. When the surface of the Earth finally became inhabitable again, thousands of years after each asteroid impact, the survivors would have emerged from their hiding places and spread across the planet--until another asteroid struck and the whole cycle was repeated. "We know that large asteroid impacts can sterilize or partially sterilize planets," says Norman Sleep, a professor of geophysics at Stanford who [presented] the theory at the fall meeting of the American Geophysical Union in San Francisco on Friday, December 14. "An asteroid a few hundred kilometers in diameter will boil off much of the ocean and leave the rest of the ocean very hot, so all that will survive will be high-temperature organisms living deep in the subsurface," he says. Rock vapor and water would fill the atmosphere, killing off any life on the surface with temperatures upwards of 1,000°C (1,800°F). The only organisms that could survive such an impact are thermophiles--heat-loving microbes--buried half a mile or more below the Earth's surface, where the effects of the burning atmosphere would have been muted to a survivable 100°C (212°F). Those organisms may have given rise to much of the life on today's Earth. Sleep calls the region where those organisms would have lived the "Goldilocks Zone"--deep enough for microbes to avoid the heat of the burning atmosphere, but not so deep that they ran afoul of the Earth's internal heat. Since there are no records of life before 3.8 billion years ago, there is no direct proof that Sleep's theory is correct. But several strands of evidence are highly suggestive. The first is that two of the three major branches of life that exist on Earth today--Archaea, Bacteria and Eukarya--began with organisms that were designed to live in extremely hot environments, the kinds that would have existed for millions of years after the impact of a large asteroid. A glance at the names of modern members of the Archaea and Bacteria branches turns up an overwhelming number of "thermos"--Thermococcus, Thermotoga, Thermoproteus and others. All of them thrive at temperatures above 80°C (176°F), with some managing to eke out an existence in conditions that would literally boil most organisms alive. (The current record-holder can survive in environments above 115 C [239 F], says Sleep.) "The roots of these two branches of the tree are clearly thermophile, which is exactly what's going to survive in a large impact," says Sleep. Where Eukarya--the branch that includes yeast, worms, corn and humans--fits into the story is less certain. "It's unclear whether Eukarya, which we are, has a thermophile root or not," says Sleep. "We may never have had a high-temperature-organism ancestor. But clearly two of the three branches look like asteroid survivors: very complex, highly-evolved organisms that are thermophile." The second strand of evidence is geophysical. Although it has long been thought that early Earth would have been rendered lifeless by continual asteroid bombardment, there are now good reasons to believe that our planet was struck by fewer than 20 large asteroids between the time of the Moon-forming impact and the first fossil signs of life. That would leave hundreds of millions of years between each asteroid strike, during which complex organisms--and life itself-- would be free to evolve. When asteroids did strike, only those organisms that could find some kind of shelter would have survived. The most obvious refuge is deep within the Earth itself, but Sleep believes there may have been another, more exotic way for early organisms to survive such Earth-shattering catastrophes. Martian invaders Perhaps, says Sleep, some of the asteroids that struck the early Earth were large enough to destroy all life on the planet, even those organisms hidden deep within the crust. There was still at least one other place where life could have survived, even flourished, before returning to Earth: Mars. Although Mars is now a frigid desert, four billion years ago it may have been a warm, water-filled oasis as friendly to life as early Earth. But could a microorganism really have survived the trip from Earth to Mars? To successfully complete the interplanetary journey, a microbe first would have to survive an asteroid impact powerful enough to free a chunk of rock from the grip of gravity. Once in space, the traveler would be faced with conditions harsher than anything found on Mars or Earth: total vacuum, subzero temperatures, harmful radiation and the passage of perhaps thousands of years before the interplanetary dart hit its target. Even then, the colonizing microbe would have to hope that some of its descendants were buried deep enough in the rock to avoid burning up in Earth's atmosphere. Sleep says these factors make the trip difficult, but not impossible. Models have shown that the initial shock of ejection from a planet isn't necessarily deadly, especially for the hardiest microbes, and especially from a small planet like Mars where the atmosphere is thin and gravity is relatively weak. "You don't sterilize a milk bottle by throwing it off your roof," he explains. And laboratory experiments have shown that earthly microbes, especially if hidden in cracks deep within a meteorite, can survive the harsh conditions of space at least for a few years. Of course, no one has tested whether they can survive for thousands of years, but there's no reason to think they can't, notes Sleep. "Conditions are not good for microorganisms, but they're not bad," he adds. So it is possible that life came from another planet--but did it really happen? So far there is no direct evidence of life on other planets or asteroids, although it is becoming clear that conditions exist, at least on Mars and Europa--one of Jupiter's inner moons-- where microbes that live comfortably in Earth's harsher climates would have felt at home. As Sleep put its, Mars "is no more uninhabitable than Antarctica"--uncomfortable for humans, but perfect for some microbes. Conclusive evidence for or against the theory only will come when scientists can examine samples from other planets and asteroids, something that is still a long way off. But Sleep says he's not frustrated by the sometimes slow pace of studying early life. "The origin of life is one of the fundamental problems of science, and it always has been. Living at a time when you can do that, it's not something I'm going to pass up," he says. Contact: Mark Shwartz, News Service Phone: 650-723-9296; E-mail: mshwartz@stanford.edu Visit Norman Sleep's home page at http://geo.stanford.edu/GP/sleep.html. An additional article on this subject is available at http://www.spacedaily.com/news/early-earth-01m.html. _____________________________________________________________________ NEW ADDITIONS TO THE ASTROBIOLOGY INDEX By David J. Thomas http://www.lyon.edu/webdata/users/dthomas/astrobiology/astrobiology.h tml 17 December 2001 [image] While astronomers have found evidence of dozens of extrasolar planets, earthlike planets have yet to be found. Above, David A. Hardy (www.astroart.org) has illustrated how an earthlike extrasolar planet might appear. This image and many others are included in David's new book, Hardyware: The Art of David A. Hardy. Articles about astrobiology, exobiology and terraformation http://www.lyon.edu/webdata/users/dthomas/astrobiology/online_article s1.html L. David, 2001. Seeking contact: Carl Sagan center to focus on life in the universe. Space.com. Articles about the biology of extreme environments (on Earth) http://www.lyon.edu/webdata/users/dthomas/astrobiology/online_article s2.html Articles about human space exploration and the microgravity environment http://www.lyon.edu/webdata/users/dthomas/astrobiology/online_article s3.html National Research Council, 2001. The Mission of Microgravity and Physical Sciences Research at NASA. National Academy Press, Washington, DC. Articles about the search for extraterrestrial intelligence (SETI) http://www.lyon.edu/webdata/users/dthomas/astrobiology/online_article s4.html Articles about evolutionary biology and chemistry http://www.lyon.edu/webdata/users/dthomas/astrobiology/online_article s5.html E. Benson, 2001. Geophysicist studies life in the early solar system. SpaceDaily. K. Leutwyler, 2001. New data kicks up "snowball earth" fight. Scientific American. Astrobiology and extreme environments book list http://www.lyon.edu/webdata/users/dthomas/astrobiology/astrobiology_b ooks.html B. Dorminey, 2001. Distant Wanderers: The Search for Planets Beyond the Solar System. Springer Verlag, Berlin. D. A. Hardy and C. Morgan, 2001. Hardyware: The Art of David A. Hardy. Paper Tiger, London. _____________________________________________________________________ CASSINI WEEKLY SIGNIFICANT EVENTS NASA/JPL release 6-12 December 2001 The most recent spacecraft telemetry was acquired from the Goldstone tracking station on Wednesday, December 12. The Cassini spacecraft is in an excellent state of health and is operating normally. See the "Present Position" web page at http://www.jpl.nasa.gov/cassini/english/where/. Recent instrument activities included two Radio and Plasma Wave Science High Frequency Receiver calibrations. Engineering activities taking place onboard the spacecraft this week include an Attitude Control Subsystem high-water mark clear and the uplink of the Mission Sequence Subsystem (MSS) D7.6.1 Modules. Execution of C29 continues to proceed normally with the ongoing Gravitational Wave Experiment, of which 16 days out of 40 days have been completed. Spacecraft health remains excellent, maintaining a quiet spacecraft on reaction wheel control. Instruments remain quiet as well with MAPS data being collected and downlinked. The Huygens Recovery Team task force had its Quarterly Progress Meeting this week. The results from the last Probe Checkout and Probe Relay Test #4 were discussed, as well as some mission and engineering analyses. The results from Probe Relay Test #4 were excellent and essentially demonstrated that the recovery mission will satisfy the mission objectives. The Spacecraft Operations Office held an internal meeting to discuss the critical milestones for the final Attitude Control Subsystem and Command & Data Subsystem Flight Software uplinks and the Saturn Orbit Insertion (SOI) critical sequence. This meeting was in response to inputs from the SOI Smart Burn algorithm review held last week. The Saturn, Cross-Discipline, Ring, and Magnetosphere Target Working Teams (TWT) held meetings last week to continue integrating the tour. The TWTs are now integrating orbits 10 through 15 to meet the next delivery milestone in February 2002. In addition, a Titan Orbiter Science Team meeting was held to integrate the period outside of +/30 minutes for Titan flybys T11 through T22. Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, CA, manages the Cassini mission for NASA's Office of Space Science, Washington, DC. _____________________________________________________________________ STARDUST STATUS REPORT NASA/JPL release 14 December 2001 There were two Deep Space Network (DSN) tracking passes during this past week, and all subsystems are normal. Stardust is currently 2.57 AU from the Sun. In preparation for the upcoming solar conjunction, the command loss timer was increased to twenty days from its present seventeen-day value. Solar conjunction, occurring from December 21 through 30, is when the angle between the Sun, Earth, and Stardust is less than three degrees. When the spacecraft looks so close to the Sun from Earth, the DSN antenna is looking directly into the Sun, making communication to and from the spacecraft unreliable. The smallest angle will occur late Christmas Eve. Though three DSN passes are scheduled during the solar conjunction, we assume that a command will not successfully reach the spacecraft. Therefore, the timer was increased to twenty days to ensure the spacecraft does not prematurely assume there is an antenna problem, invoke safe mode and swap antennas. Based on the existing DSN schedule, the pass on December 17th is the last time we expect to reliably send a command to the spacecraft. January 4th is the first opportunity after the solar conjunction to successfully send a command to Stardust. Radio scientists will use the DSN passes scheduled during the conjunction period to measure the effects of the Sun as the signal passes close by it. For more information on the Stardust mission--the first ever comet sample return mission--please visit the Stardust home page at http://stardust.jpl.nasa.gov. _____________________________________________________________________ End Marsbugs, Volume 8, Number 48.