MARSBUGS: The Electronic Astrobiology Newsletter Volume 6, Number 35, 1 November 1999. Editors: Dr. David J. Thomas, Biology and Chemistry Division, Lyon College, Batesville, AR 72503-2317, USA. Dthomas@lyon.edu or marsbugs@aol.com 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 quarterly 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://www.lyon.edu/webdata/users/dthomas/marsbugs/marsbugs.html . 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 out of 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, planetary biology, primordial evolution, space physiology, biological life support systems, and human habitation of space and other planets. ---------------------------------------------------------------- CONTENTS 1) PLANETARY SOCIETY'S MARS MICROPHONE READY FOR DUTY Planetary Society release 2) THE "OASIS CRATER" IDEA WILL NOT WORK [FOR TERRAFORMATION] By Robert Alan Mole 3) THE DESTRUCTIVE EFFECT OF COMETS FOR TERRAFORMING (AND A POSSIBLE SOLUTION) By Robert Alan Mole 4) CLOSEST-EVER PICTURE OF VOLCANIC MOON IO RELEASED JPL release 5) MARS CLIMATE ORBITER INVESTIGATION BOARD UPDATE NASA release 99-124 6) WELCH HONOREE HAS SHED NEW LIGHT ON MICROBIAL LIFE By Todd Ackerman 7) OXYGEN MAY BE CAUSE OF FIRST SNOWBALL EARTH Pennsylvania State University release 8) LIFE BEYOND EARTH From "PBS Picks" 9) THIS WEEK ON GALILEO JPL release 10) MARS GLOBAL SURVEYOR STATUS REPORT JPL release 11) NEW MARS GLOBAL SURVEYOR IMAGE By Ron Baalke 12) MARS POLAR LANDER MISSION STATUS JPL release 13) STARDUST STATUS REPORTS JPL releases ---------------------------------------------------------------- PLANETARY SOCIETY'S MARS MICROPHONE READY FOR DUTY Planetary Society release [http://www.planetary.org/news/articlearchive/headlines/1999/hea dln-101899.html] 18 October 1999 Mars Polar Lander is nearing Mars for its scheduled December 3 arrival. A trajectory correction maneuver will be applied this week to target it for the final selected landing site on Mars (76 degrees south latitude, 195 degrees west longitude). Following the loss of Mars Climate Orbiter due to a navigation error, this maneuver and all the project navigation is being watched closely. The Planetary Society's Mars Microphone is on-board the lander, and as far as we can tell, in good shape. We hope to hear sounds from Mars within the first day after landing. The Mars Polar Lander project just completed its Operations Readiness Test, which involved simulating commands and telemetry for all the science data. Microphone data will be obtained at the beginning of the mission as part of the LIDAR instrument data stream. The University of California built the microphone, which is included within the Russian-built LIDAR experiment. The LIDAR is the first Russian instrument to fly on a U.S. planetary spacecraft. It will measure the haziness and particle content of the atmosphere. Communications from the spacecraft had been planned to be relayed through Mars Climate Orbiter once it landed. Now, however, it will go over backup communication links - direct to Earth from the lander (at lower data rates, but with more frequent communications periods) and through the Mars Global Surveyor, now carrying out a successful mission in Mars orbit. The MGS link will not occur, however, until after the first few days of landing, since it will be preoccupied with data from the Deep Space 2 microprobes, which are also landing on Mars this December 3. The data received from the lander depends on how much power is available for the spacecraft and how accurately the antenna is pointed to Earth. The power depends on how much of the solar panels face the sun and how hazy the atmosphere is and whether any dust gets on the solar panel. None of these conditions will be known until the spacecraft lands. But assuming all goes as expected (and it could go better, or worse), microphone data will be part of the early data streams from the spacecraft. Once it is received, it will take several hours to process (after all, no one has ever received microphone data from Mars before), and then it will be made available to the world. You will be able to hear the first sounds from Mars as part of our Planetfest '99 program, and witness the first three days of the Mars Polar Lander mission. The first sounds will most likely be that of the spacecraft itself--those of the robotic arm being unstowed and deployed. We want to experience the loudest sounds we can find at first. By the second or third day, we will try to correlate the sounds recording with periods of quietness, to see what natural sounds we might discover on Mars. The Planetary Society funded the microphone on-board the Mars Polar Lander at no cost to NASA and with no interference to the project's science goals. We owe tremendous gratitude to our Russian colleagues from the Space Research Institute who integrated into their LIDAR instrument and tested it, as well as to the University of California, Berkeley, Space Science Labs who built it, the Mars Volatiles and Climate Surveyor payload team, and the Mars Surveyor Operations Project personnel now conducting the mission. ---------------------------------------------------------------- THE "OASIS CRATER" IDEA WILL NOT WORK By Robert Alan Mole Around 1980, Dr. A. W. G. Kunze proposed the idea of using a 67km asteroid to punch a 41 km deep crater into the surface of Mars. At the bottom, the natural increase in air pressure with depth was to provide a 500mb pressure of nearly pure CO2, with warm temperatures, liquid water, and the possibility of plant growth. Kunze named this plan an "Oasis Crater" in an attractive analogy to an oasis in the middle of a barren desert (1). The idea has continued to be mentioned ever since, most recently by Fogg in his terraforming book of 1994 (2). Unfortunately, the idea will not work and we should discard it and bend our efforts to more promising plans. We simply cannot make such deep craters. It is true that small impacts make craters with depths of about one fifth their radius, but beyond a certain point the depth vs diameter curve bends over and flattens out, and depth no longer increases with diameter. This is called the "transition diameter", and on Mars it occurs at about 5-10 km diameter and 1-2 km depth. The largest crater on Mars is 400 km in diameter, but only 4 km in depth. Depth vs Diameter for Actual Martian Craters (After Carr (3)). Strom et al say, "The transition diameter is seen to be roughly inversely proportional to surface gravity [of the planet involved]... the simple-complex transitions are almost certainly the result of material failure during the modification state of the cratering process..." (4). Modification includes rebound of the floor and collapse of the crater walls. The dependence on gravity simply means that the weight of the overlying rock, (and hence the hydrostatic pressure and other forces) are greater under higher gravity. Apparently the rock on the crater floor is either molten or at least viscous just after the impact, and surges up to fill much of the crater for depths over 2-4 km. In any event, the deepest crater is only 4 km, so far short of the desired 40 km depth that only a tiny increase in pressure (from 6.1 to 10 mbar) will occur. We might, of course, aim our asteroid to make a crater in the bottom of the Hellas basin, which is already 4 km deep, to try for a total depth of 8km. But the scale height--the altitude difference for a doubling of pressure--is 7.5 km on Mars, so 8 km would only raise the pressure from 6 to 12 mbar. Nothing can live at such a pressure, so this does no good. In actuality, it is not clear that we could make a pit in the bottom of Hellas. Hydrostatic pressure vs the strength of martian rock may limit maximum depth to 4 km anywhere. Hellas' floor is suspiciously smooth, with no deep craters anywhere in its thousand-km reach. It is quite possible that craters simply fill up as soon as they form. It has been suggested that a deep crater might be temporary in geologic terms but rather permanent in human terms. Might it last, say, a thousand years? I believe that under the pressures 40 km down, the rock is plastic, a thick viscoelastic fluid, and would flow back in quickly in a few hours. Exposed surfaces would be solid of course, but from the walls would come landslides while rock fountains spewed from the floor and water poured down 35 km from kilometers-thick aquifers punched through by the impact, creating an ocean on the bottom. Great earthquakes and tidal waves would complete the picture, which is not promising for a colony (though interesting). I've asked a USGS geologist who agrees with the overall scenario and estimates the crater fills quickly.i Still, we may someday bring icy asteroids to Mars for their volatile content, and they'll have to fall somewhere, so we could direct them to Hellas. It can't hurt to try. Also, we won't need 67 km monsters--a 2 km model will do all that can be done, making a crater 20 km across and 4 km deep. Finally, if we can sublime the south polar cap and material from the regolith, then we may produce a surface pressure anywhere between 60 and 2000 mb (there is great uncertainty just how much CO2 is present and accessible.) In the case where we can produce only a thin atmosphere, a doubling of pressure might make the difference between a sterile and a viable environment, and in this case the oasis crater idea might help. But note that we must first increase atmospheric pressure to ten times its present level, and that will be the principal effect. So the idea that we can just make a 40 km deep crater and have an oasis with the present atmosphere simply won't work. A martian Utopia cannot be created this way. We can't make a Heaven out of Hellas. References 1. Noted in Oberg, J. E., 1981, New Earths: Terraforming Other Planets for Humanity, Stackpole Books, Harrisburg, PA. "Dr. A. W. G. Kunze, of the University of Akron's Department of Geology, Personal Communication." 2. Fogg, M. J., 1995, Terraforming: Engineering Planetary Environments, Society of Automotive Engineers, Warrendale, PA. 3. Carr, M. H., 1981, The Surface of Mars, Yale Planetary Exploration Series, New Haven, CT. 4. Stromm, R. G., S. K. Croft and N. E. Barlow, 1992 "The Martian Impact Cratering Record," in Mars (H. H. Kieffer, B. M. Jakosky, C. W. Snyder and M. S. Matthews, eds), The University of Arizona Press, Tucson, AZ. Endnote USGS Internet "Ask a Geologist" service, response from Dave Miller, geologist: "I think the answer, regardless of the exact number of minutes or hours, is "Far shorter than it takes to start a colony!" "On earth, a crater doesn't form a deep hole because virtually instantaneous rebound of the viscous lower crust domes all the floor of the crater. (As well as all sorts of back-filling mechanisms like you described.) My guess he is that similar process would operate on Mars, much as you have described. If so the time involved is minutes or hours, not days or years." Contact information Robert Alan Mole 1441 Mariposa Ave. Boulder, CO 80302 (303) 440-7385 ramole@aol.com ---------------------------------------------------------------- THE DESTRUCTIVE EFFECT OF COMETS FOR TERRAFORMING (AND A POSSIBLE SOLUTION) By Robert Alan Mole 22 October 1999 There are many plans to strike Mars with comets made of frozen gasses and thereby supply it with nitrogen or water. Typical is one in James Oberg's New Earths: "If there is insufficient nitrogen frozen into the martian regolith to supply plants with enough to grow, terraforming might still be accomplished... Nor, ultimately should the possibility of importing nitrogen (perhaps from Titan or Triton or some other distant space snowball) be ignored. Sufficient nitrogen could be contained in objects approximately 200 km in diameter, which could reasonably be expected to be movable early in a terraforming program." (1) (This appears to be mass enough to give a full earth- normal partial pressure of 800 mb of nitrogen.) We should consider the effect of the impact of such a body, or an equivalent mass of smaller ones. Meteor Crater in Arizona is 3/4 mile wide by 600 feet deep, and is thought to have been caused by the impact of a body 150 feet in diameter. Assuming similar ratios hold for Mars, the crater depth for any body will be four times its diameter, and the crater diameter 26 times that of the impactor. (Lower speed impacts, typical of asteroid strikes, make smaller holes; higher speeds typical of comets larger ones, but the above is probably a good average for a high speed body coming in from Jupiter or Saturn.) A 200 km body would then make a crater 5200 km wide by 800 km deep. Mars' diameter is just 6700 km so such an impact would obliterate one face and spew magma over the rest, covering everything to an average depth of 100 km. We would indeed create a New Mars, but not one that anyone would want. To avoid this ruin, we could break the 200 km monster into one km chunks. Unfortunately there will be a lot of them--8,000,000 to be exact. Each will make a 26 km diameter crater 4 km deep, covering 530 square km. Alas, eight million such craters will cover a large area: 8x106 x 530 km2 is 4.25 x109 km2. But Mars' surface is only 1.4x108km2--one thirtieth as big. So every square meter of Mars will be blasted and excavated to a depth of 4 km--not once but thirty times! Afterwards we will be able to give a definitive answer to the question Is there Life on Mars? No. A Possible Answer Perhaps we can break the comets into such small parts that they burn up in the upper atmosphere, doing no harm and only heating the atmosphere in the process. The smaller the pieces the higher they burn up. Clearly large pieces carry most of their energy to the lower atmosphere--and larger pieces all way to the ground--while fine dust expends itself at a high altitude. Since heating the atmosphere at high altitude to a high temperature may leave the air molecules moving at more than escape velocity, this can lead to a net loss of atmosphere; and so we should avoid a thick rain of dust size particles. Therefore I will assume brick size or chair size blocks, distributed over a large area like most of a hemisphere, heating bubbles or long columns of air, which then dissipate their heat by radiation to the ground, space, and the rest of the atmosphere, or by mixing. Nevertheless, if the bombardment is too dense we could end up with an atmosphere at thousands of degrees, leaking to space because its temperature and the average molecular speed are too high. To get an idea of what limitation this puts on bombardment rate, I will assume the rate of heat delivery should not exceed that from the natural solar incidence. We can surround the planet with reflectors and stop the sunlight completely, so that the heat-in rate stays the same, only with kinetic energy substituted for solar energy. I do not claim this is optimal, only that it lets us make an initial estimate of practicality. Will this rate let us provide an atmosphere in ten years or ten million? Mars' solar incidence is, 6.7 x 1023 J/year, while a 200 kilometer sphere of solid nitrogeni at 7.5 kilometers per second has a kinetic energy of 9.6 x 1025 J, or 142 years' worth of solar energy. We cannot assume that we can bombard at a higher rate because Mars is cold anyway and needs to be warmed. Standard calculations show warming needed is less than ten years' solar incidence. Nor can we eject the heat more rapidly by increasing Mars' albedo--it is already approximately 1.0, the maximum possible. But we could allow the planet to run a bit warm for while, radiating, say, four times the energy to space as it now does, which would cut the time to 36 years.** (Or 45 years and we would not need the sunshade.) This is a reasonable time for terraforming, and we should note that this is for 800 millibars partial pressure of nitrogen, as on earth, whereas we need only one to ten millibars for plant growth, and we could achieve that result in a few months. It has also been written that one could terraform earth's moon in a similar fashion. The atmosphere would be "temporary" in terms of geological time, but would last over 10,000 years, or "forever" in terms of human history (1). But this too would involve large bodies aimed at the moon, which raises a safety issue. What if one misses and hits earth? If a 6 km asteroid killed the dinosaurs we can not risk a 200 km monster hitting us. Therefore, only clouds of fragments small enough to self- destruct harmlessly high in earth's atmosphere should ever be aimed at the moon. These calculations are preliminary but promising. Yet whatever means we use to solve the problem we must address it. It is not enough to calculate volume requirements for giving Mars an atmosphere. We must also arrange the impacts so the planet retains a lithosphere. References 1. Oberg, J E, "NEW EARTHS: Terraforming Other Planets For Humanity" Stackpole Books, Harrisburg, PA, 1981. 2. McKay, C.P., Toon, O.B.,Kasting, J.F., Making Mars Habitable, Nature, v352, pp 489-496, Aug 1991. Endnotes iLiquid nitrogen has a density of 0.81 grams per cc and I have assumed the same for solid. **Mars' average temperature is 217K, and radiation rate is proportional to the fourth power of the temperature, so for four times the radiation rate we need to 217 K. times the fourth root of 4 = 1.41 times 217K = 307 K. = 33C = 92 F. This seems acceptable. It would also help warm the surface and regolith. Contact information Robert Alan Mole 1441 Mariposa Ave. Boulder, CO 80302 (303) 440-7385 ramole@aol.com ---------------------------------------------------------------- CLOSEST-EVER PICTURE OF VOLCANIC MOON IO RELEASED JPL release 22 October 1999 The closest-ever image of Jupiter's moon Io, taken during a daring flyby of the volcanic moon by NASA's Galileo spacecraft on October 10, 1999, shows a lava field near the center of an erupting volcano. The image, available at http://www.jpl.nasa.gov/pictures/io , was taken from an altitude of 671 kilometers (417 miles) and is 50 times better than the previous best, taken by the Voyager spacecraft in 1979. Visible in the image are new lava flows from the volcanic center named Pillan, an area with erupting lava hotter than any known eruption that occurred on Earth within billions of years. Scientists will be studying this image to determine the characteristics of the eruption, along with other data due to be sent back by the spacecraft in coming weeks. Not surprisingly, fierce radiation took its toll on the spacecraft. Io's orbit lies in a region of intense radiation from Jupiter's radiation belts, which can affect the performance of or even knock out various spacecraft instruments. A mere fraction of the dose that Galileo received would be fatal to a human. Because of the radiation risk, the Io encounters were scheduled for the end of the two-year extended mission, after the spacecraft had already fulfilled its other mission objectives. Most of the Io images were taken using a "fast camera" mode, where the camera itself pre-processes the image to average the brightness in adjacent parts of the picture. Galileo engineers say it appears that Jupiter's radiation caused the process to get out of sync, which degraded the quality of the images. Fortunately, images that were taken in other camera modes, including the newly released image, apparently did not suffer ill effects from the radiation. "When we're flying the spacecraft through this high-radiation zone near Io's orbit, we have to plan for the likely radiation and figure out how to deal with it," said Galileo Project Manager Jim Erickson. "We used several different modes to see how each would work. Now that we know this particular camera mode didn't work well amidst the radiation, we'll use other modes from our six different types for the next Io flyby." That second Io flyby is scheduled for November 25 at an altitude of only 186 miles (300 kilometers). Galileo's original mission was to spend two years studying Jupiter, its moons and magnetic environment. That mission ended in December 1997, then was followed by a two-year extended mission scheduled to end in January 2000. Galileo, the first spacecraft to orbit Jupiter, has revolutionized our knowledge of the giant planet and its moons and has provided thousands of colorful images. During the October 10 Io flyby, the radiation also apparently triggered a problem with Galileo's near-infrared mapping spectrometer. The instrument has a grating that allows it to measure different wavelengths of light as they are reflected onto a sensor. This enables the instrument to produce a spectrum of the light from objects it observes. During the flyby, the grating did not move as it should have, which means that only one set of wavelengths was measured instead of the complete spectrum. The resulting data provides maps at each of several wavelengths in very high spatial resolution. These maps can be used to show the distribution of materials on the surface and measure the temperature of the lava in Io's volcanoes, but detailed spectral information for identifying materials on the surface will be limited to the early part of the encounter where full spectral data were acquired. The Galileo flight team is still evaluating the status of another instrument, the ultraviolet spectrometer, which has been acting up for two months. Since this instrument was not scheduled to be used during the Io encounter, it was switched off while engineers diagnose its grating problem. Additional information and pictures taken by the Galileo spacecraft are available at the mission's web site at http://galileo.jpl.nasa.gov. Galileo was launched from the Space Shuttle Atlantis on October 18, 1989. It entered orbit around Jupiter on December 7, 1995. JPL manages the Galileo mission for NASA's Office of Space Science, Washington, DC. The California Institute of Technology, Pasadena, CA, operates JPL for NASA. ---------------------------------------------------------------- MARS CLIMATE ORBITER INVESTIGATION BOARD UPDATE NASA release 99-124 22 October 1999 The NASA review board investigating the loss of Mars Climate Orbiter has completed its first round of meetings, and has begun preparing a report on its initial findings. "Mission team members from the Jet Propulsion Laboratory and Lockheed Martin have responded fully to all of our requests for information," said board chairman Art Stephenson, director of NASA's Marshall Space Flight Center, Huntsville, AL. "We clearly will have some specific recommendations relevant to helping ensure the successful landing of the Mars Polar Lander, and we have already begun providing informal feedback to the lander team, given their tight schedule. We have also made good progress towards identifying the root causes of the orbiter mission failure." The failure review board will brief officials at NASA Headquarters on its initial findings on October 29. The board will then deliver an initial written report to NASA by November 5. A second report due by February 1, 2000, will address lessons learned and recommendations to improve NASA processes to reduce the probability of similar incidents in the future. Mars Polar Lander is scheduled to land on layered terrain near the south pole of Mars on December 3. The next thruster firing to fine-tune the spacecraft's flight path for its approach to Mars is now scheduled for October 30. Mars Climate Orbiter was lost as it was entering orbit around Mars on September 23. The orbiter and lander are part of a series of missions in a long- term program of Mars exploration managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. JPL's industrial partner is Lockheed Martin Astronautics, Denver, CO. JPL is a division of the California Institute of Technology, Pasadena, CA. ---------------------------------------------------------------- WELCH HONOREE HAS SHED NEW LIGHT ON MICROBIAL LIFE By Todd Ackerman Houston Chronicle 24 October 1999 He had a brief fling with media stardom because of his work analyzing the rock that provided evidence microbial life may have once existed on Mars. But Richard Zare's lasting renown is likely to be for pioneering laser devices and techniques, now common in laboratories around the world, that detect and identify molecules in unimaginably small concentrations, whether inside meteorites or inside cells. Zare's biggest splash came with the Mars rock and his laser's determination that organic matter in it was not scattered randomly but clumped together in globules of carbonate. Get the full story at http://www.chron.com/cgi- bin/auth/story.mpl/content/interactive/space/news/99/991027.html ---------------------------------------------------------------- OXYGEN MAY BE CAUSE OF FIRST SNOWBALL EARTH Pennsylvania State University release 27 October 1999 Increasing amounts of oxygen in the atmosphere could have triggered the first of three past episodes when the Earth became a giant snowball, covered from pole to pole by ice and frozen oceans, according to a Penn State researcher. "We have convincing evidence that at least six of the seven continents were once glaciated, and we also have evidence that some of these continents were near the equator when they were covered with ice," says Dr. James F. Kasting, professor of geosciences and meteorology. "Two of these global glaciations occurred at 600 and 750 million years ago, but the earliest occurred at 2.3 billion years ago." According to Kasting, if it is assumed that the magnetic evidence for glaciation at the equator is correct, then only two possible explanations for equatorial glaciation exist. One is that the Earth's tilt, which is now at 23.5 degrees from vertical, was higher than about 54 degrees from vertical. This would have positioned Earth so that the poles received the most solar energy and the equator would receive the least, creating a glacier around the middle but still leaving the poles unfrozen. The other possibility, which is the one that Kasting leans toward now, is that the greenhouse gases in the atmosphere fell low enough so that over millions of years, glaciers gradually encroached from the poles to 30 degrees from the equator. Then, in about 1,000 years, the remainder of the Earth rapidly froze due to the great reflectivity of the already ice-covered areas and their inability to capture heat from the sun. The entire Earth became a snowball with oceans frozen to more than a half mile deep. "For the latest two glaciations, carbon dioxide levels fell low enough to begin the glaciation process. However, for the earliest glaciation, the key may have been methane," Kasting told attendees at the annual meeting of the Geological Society of America today (October 27) in Denver. "The earliest known snowball Earth occurred around the time that oxygen levels in the atmosphere began to rise," says Kasting, who is a member of the Penn State Astrobiology Center. "Before then, methane was a major greenhouse gas in the atmosphere in addition to carbon dioxide and water vapor." As oxygen levels increased, methane levels decreased dramatically and carbon dioxide levels had not built up enough to compensate, allowing the Earth to cool. Oxygen levels need only reach a hundredth of a percent of present-day oxygen levels to convert the methane atmosphere completely. Once the Earth is snow covered, it takes 5 to 10 million years for the natural activity of volcanoes to increase carbon dioxide enough to melt the glaciers. Regardless of the greenhouse gas involved, the pattern of freezing and defrosting would be the same. Because the sun has been constantly increasing in brightness, it would take more greenhouse gas in the past to compensate for the fainter sun. For the glaciations at 600 and 750 million years ago, estimates are that carbon dioxide levels equal to recent pre- industrial levels or up to three times pre-industrial levels would have been sufficient for snowball Earth to occur. Because many continents existed in the warm equatorial areas during the most recent glaciations, Kasting believes that rapid weathering of calcium and magnesium silicate rocks, which consumes carbon dioxide, lowered levels sufficient to cool things. "It would have taken nearly 300 times present levels of carbon dioxide to bring the Earth out of its ice cover," says Kasting. "Then, once the high reflectivity ice was gone, the carbon dioxide would have overcompensated and the Earth would become very warm until rapid weathering would remove carbon dioxide from the atmosphere." One reason that many scientists initially rejected the snowball Earth theory was that biological evidence does not suggest that the various forms of life on Earth branched out from the latest total glaciation. A variety of life forms had to survive from before the glaciation, which is difficult to imagine on an ice- covered world. Perhaps the ancestors of life today survived in refuges like hot springs or near undersea thermal vents. "The biological puzzle of snowball Earth is very interesting," says Kasting. "Events suggest that life was more robust than we thought and that the Earth's climate was much less stable than we assumed." Dr. Kasting is at (814) 865-3207 or at kasting@essc.psu.edu by email. ---------------------------------------------------------------- LIFE BEYOND EARTH From "PBS Picks" 1 November 1999 Does life exist beyond Earth? This ancient question has consumed stargazers for centuries. Yet only in the last few decades have humans developed the tools to actively search for extraterrestrial life. Astronomers today are finding evidence of planets orbiting distant stars. Others are trying to detect radio signals sent by intelligent aliens. The discovery of life beyond Earth would be without parallel in its impact on human thought. "Life Beyond Earth," a two-hour special airing on PBS Wednesday, November 10, 1999, 8:00 PM ET (check local listings), tells the story of humanity's search for extraterrestrial life. The program explains why many scientists believe that life is abundant in the universe and examines how a signal from aliens could change the course of civilization. The groundbreaking special was created and is hosted by science writer Timothy Ferris ("The Creation of the Universe"). Scientists who appear in LIFE BEYOND EARTH include biologist Norman Pace, paleontologist Stephen Jay Gould, complexity theorist Stuart Kauffman, neurobiologist Gerald Edelman, astronomers France Cordova, David Grinspoon and Paul Horowitz and physicists J. Richard Gott, III and Freeman Dyson. Filmed in Italy, California, Hawaii, Montana and New Mexico and at Harvard, Princeton and Stanford universities, the program features innovative animated simulations and a memorable musical score. For the complete story, see http://www.pbs.org/whatson/1999/fall/lifebeyondearth.html ---------------------------------------------------------------- THIS WEEK ON GALILEO JPL release 25-31 October 1999 Galileo's primary activity this week is the continued return of science data acquired during the spacecraft's close flyby of Io earlier this month. Observations made during the flyby are safely stored on Galileo's onboard tape recorder. This week's data is returned from observations made by the Near-Infrared Mapping Spectrometer (NIMS) and Solid-State Imaging camera (SSI). Data playback is interrupted twice this week. On Tuesday, the spacecraft performs a small turn to keep its radio antenna pointed to Earth. On Wednesday, Galileo performs a standard gyroscope performance test. First on the playback schedule is the return of an observation taken by SSI. The observation contains images of a region of Io's surface near the terminator (or line dividing night from day). The oblique lighting provides conditions that are optimal for studying the topography of a region containing the Hi'iaka caldera. Next, NIMS returns a regional observation of Io designed to study surface composition and detect thermal emissions. The next pair of observations are returned by SSI and NIMS, and focus on the Pillan plume. The geometry of both observations is such that the Pillan hot spot was situated on Io's limb as seen from the spacecraft. If Pillan was active during the observations, its plume will be seen against the dark sky above the limb. The data will provide scientists with the best look to date at a plume's size, shape, and composition. NIMS returns a similar observation that may contain a plume of the Pele volcano. This observation's geometry is such that the plume, if present, will be seen with Jupiter's disk in the background. The SSI camera then returns a regional observation of Io. The images taken during this observation will be combined with images taken in July to produce stereo views of the region. Following on the schedule is the return of a second regional scan of Io performed by NIMS. SSI then returns an observation that contains a color view of Io's full disk, including the best color coverage of the region of Io containing the Loki and Pillan volcanoes, with the Acala region on Io's limb. SSI also returns an observation of Io while Jupiter eclipsed it from the Sun. In this color image, the volcanic regions of Loki, Pele, Pillan and Marduk are on Io's limb. This geometry will facilitate the identification of plumes that may be present. In addition, comparison of images taken through different color filters will enable scientists to measure hot spot temperatures and possibly identify the nature and source of diffuse atmospheric emissions. Toward the end of the week, Galileo starts another pass through the observations stored on the tape recorder. This pass allows replay of data lost in transmission to Earth, reprocessing of data using different parameters, or return of additional new data. SSI returns two observations this week. The first observation contains high-resolution images of the Pele region. The images were taken with Pele in darkness with the hope of catching hot glowing lava near Pele's volcanic vent. The next observation consists of high-resolution images of the Pillan volcanic region, taken at daybreak on Io with oblique viewing geometry. For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page or one of its mirror sites: http://galileo.jpl.nasa.gov http://www.jpl.nasa.gov/galileo http://galileo.ivv.nasa.gov ---------------------------------------------------------------- MARS GLOBAL SURVEYOR STATUS REPORT JPL release 21 October 1999 Launch / Days since Launch = Nov 7, 1996 / 1079 days Start of Mapping / Days since Start of Mapping = April 1, 1999 / 203 days Last Orbit Covered by this Report = 2774 Total Orbits = 4456 Total Mapping Orbits = 2774 Recent events The mm008 sequence continues executing nominally and will continue execution through November 17. Over the last week there have been several HGA position error counts (35 counts on 10/14, 37 counts on 10/17, and 35 counts 10/21) associated with the start of the HGA rewinds that occur every orbit. We are currently analyzing the spacecraft telemetry to determine the cause of the "sticky" gimbals. In the meantime a change has been approved to increase the fault protection threshold to prevent the on-board redundancy management software from swapping to the B-side HGA gimbal drive electronics in response to this recent behavior. HGA anomaly The HGA inner gimbal angle continues to decrease and is currently at 74.9 degrees. The inner gimbal angle will continue decreasing, reaching the location of the gimbal obstruction at 41.5 deg in early February. Work continues on the design and implementation of a new mapping data collection and return plan that will maximize the science data return for the remainder of the nominal mapping mission. Spacecraft health All other subsystems continue to report nominal status. Uplinks There have been 21 uplinks to the spacecraft during the last week, including new star catalogs and ephemeris files, and instrument command loads. Total command files radiated to the spacecraft since launch is 3998. Upcoming events The mm009 sequence development kickoff meeting is scheduled for November 2, with uplink preliminary scheduled for November 15. ---------------------------------------------------------------- NEW MARS GLOBAL SURVEYOR IMAGE By Ron Baalke 22 October 1999 The following new image taken by the Mars Global Surveyor spacecraft is now available: Possible Rootless Cones or Pseudocraters on Mar The image resides on the Mars Global Surveyor web site at http://mars.jpl.nasa.gov/mgs/msss/camera/images/index.html The image caption is appended below. Mars Global Surveyor was launched in November 1996 and has been in Mars orbit since September 1997. It began its primary mapping mission on March 8, 1999. Mars Global Surveyor is the first mission in a long-term program of Mars exploration known as the Mars Surveyor Program that is managed by JPL for NASA's Office of Space Science, Washington, DC. Malin Space Science Systems (MSSS) and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO. Mars Global Surveyor Mars Orbiter Camera Possible Rootless Cones or Pseudocraters on Mars MGS MOC Release #MOC2-186, 22 October 1999 High-resolution images from the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) have revealed small cone-shaped structures on lava flows in southern Elysium Planitia, Marte Valles, and northwestern Amazonis Planitia in the northern hemisphere of the red planet. The most likely interpretation of these cones is that they may be volcanic features known as "pseudocraters" or "rootless cones". They share several key characteristics with pseudocraters on Earth: they are distributed in small clusters independent of structural patterns, are superimposed on fresh lava flows, and they do not appear to have erupted lavas themselves. The white box in the picture above left shows the location of one of the MOC images of possible psuedocraters on Mars. The white box is drawn upon a MOC red wide angle context image acquired at the same time as the high resolution view, shown on the right above. Located in northwestern Amazonis Planitia near 24.8°N, 171.3°W, both the context image and high-resolution view are illuminated from the lower left. The high resolution view shows several possible psuedocraters (cone-shaped features with holes or pits at their summits) that occur on top of a rough- textured lava plain. The context frame covers an area 115 km (71 mi) across, the high-resolution view is 3 km (1.9 mi) across. Pseudocraters form by explosions due to the interaction of molten lava with a water-rich surface. Possible martian pseudocraters are of interest because they may mark the locations of shallow water or ice at the time the lava was emplaced. Viking Orbiter images have shown structures in other regions of Mars that were interpreted to be pseudocraters, but the interpretations were uncertain because the morphology was poorly resolved, it was unclear if they occurred on volcanic surfaces, and they have diameters as much as a factor of 3 larger than terrestrial pseudocraters. The cone-shaped morphology is well resolved in the cones imaged by MOC, and they have basal diameters of less than 250 m (273 yards), consistent with terrestrial examples. The cones rest on a surface with a distinctive morphology consisting of ridged plates that have rafted apart, which MOC team members have interpreted as the surface of voluminous lava flows. The surface shown here (above right) looks relatively fresh and has very few impact craters on it, which suggests that the lava flows and the cones are both geologically young. However, MOC images in other areas reveal such apparently young surfaces being exhumed (presumably by wind erosion) from beneath a blanket of overlying material. Impact processes may harden the blanket, or cover it with materials that cannot be removed by wind, so the wind erosion leaves behind elevated "pedestal craters". The cones shown here are not typical of pedestal craters, but it is important to consider this alternative interpretation. MGS MOC first began taking pictures of Mars in mid-September 1997. The planet that has been revealed by this camera is often strange, new, and exciting. The possibility that lava and water or ice have interacted to create features like psuedocraters indicates that Mars has had a diverse and complex past that researchers are only just begining to understand. The pictures shown here are the subject of a talk on MOC views of volcanism on Mars being presented in an invited talk at the Geological Society of America (GSA) Annual Meeting in Denver, Colorado on Monday, October 25, 1999, by MOC scientist Alfred McEwen of the University of Arizona, Tucson. Image credit: NASA/JPL/Malin Space Science Systems and University of Arizona ---------------------------------------------------------------- MARS POLAR LANDER MISSION STATUS JPL release 30 October 1999 NASA's Mars Polar Lander spacecraft successfully fired its thrusters for 12 seconds this morning to fine-tune its flight path for arrival at the Martian south pole on December 3. Flight controllers said the spacecraft performed as planned and that preliminary data show the desired trajectory change was achieved. The thruster firing began at 10:28 AM Pacific Daylight Time. Previous thruster firings were accomplished on January 21, March 15, and September 1. The next thruster firing is scheduled for November 30. The landing site is located at 76 degrees south latitude and 195 degrees west longitude, near the northern edge of the layered terrain in the vicinity of the Martian south pole. The lander is now about 14.3 million kilometers (about 8.9 million miles) from Mars, traveling at a speed of 4.8 kilometers per second (about 10,700 miles per hour) relative to Mars. The spacecraft is about 228 million kilometers (about 142 million miles) from Earth, and has traveled along an arcing flight path of about 690 million kilometers (about 429 million miles) through space since launch from Cape Canaveral, Florida, on January 3, 1999. For more information on the mission, see http://www.jpl.nasa.gov/marsnews/ Mars Polar Lander is managed for NASA's Office of Space Science by the Jet Propulsion Laboratory. JPL is a division of the California Institute of Technology, Pasadena, CA. ---------------------------------------------------------------- STARDUST STATUS REPORTS JPL releases 22 October 1999 The Stardust spacecraft continues to perform normally in cruise sequence SC010. The flight team at Lockheed Martin Astronautics (LMA) had multiple communications sessions with the spacecraft during the past week and were successful in taking 9 Navigation Camera images using 2 exposures and stepping through all 8 filters. The mirror was also successfully moved during this time period, enabling the camera to image stars without looking through the periscope. The images will be downlinked in November during the next scheduled pass using the High Gain Antenna. Stardust will be the first spacecraft ever to bring cometary material back to Earth for analysis by scientists worldwide. Comets are believed to contain the original building blocks of the planets and perhaps those of life itself. Early in Earth's history, comets laden with water ice slammed into the planet, maybe providing the source of our oceans. When STARDUST returns its pristine comet samples, scientists will be able to examine for the first time the key ingredients of the original recipe that created the planets. Stardust was built Lockheed Martin Astronautics and is managed by NASA's Jet Propulsion Laboratory, in Pasadena, California. The principal investigator of the mission is space particle scientist Dr. Donald Brownlee of the University of Washington. Dr. Kenneth Atkins of JPL is the project manager. Stardust's main objective is to collect and bring to Earth particles flying off the nucleus of Comet Wild-2 in January 2004. It will also bring back samples of interstellar dust including the recently discovered dust streaming into the solar system from other stars. The spacecraft will send back pictures of Comet Wild-2, count the comet particles striking the spacecraft, and produce real-time analyses of the composition of the material coming off the comet. A unique substance called aerogel is the medium that will be used to catch and preserve comet samples. When STARDUST swings by Earth in January 2006, the samples encased in a reentry capsule will be jettisoned and parachute to a pre-selected site in the Utah desert. 29 October 1999 The Stardust spacecraft continues to perform normally in cruise sequence SC010. This last week was quiet compared to the two previous weeks where we had multiple communications session per week supporting the All Stellar "toe dip" tests and taking Navigation Camera images. Work has progressed steadily on the flight software patch to fix a multiple thruster firings issue when in All-Stellar mode. This patch will either be sent up to the spacecraft late today or early next week, paving the way to going All-Stellar in the near future. Boeing management visited JPL and met with project people of missions recently launched by Delta's, including the Stardust Project. Stardust had a near-perfect injection aboard a Delta 2 rocket during its launch last February, requiring no maneuver to correct injection errors. Stardust is the fourth under NASA's Discovery Program of low- cost science missions, following Lunar Prospector, Mars Pathfinder and the Near Earth Asteroid Rendezvous (NEAR). The goal of NASA's Discovery Program is to launch many smaller missions with shorter development time that perform focused science at lower cost. JPL is a division of the California Institute of Technology, Pasadena, California. 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 Vol. 6, No. 35