Category: Earth Observation

Artist’s concept of CloudSat and Calipso orbiting Earth. Image credit: NASA Click to enlarge
Two NASA satellites, planned for launch no earlier than Oct. 26, will give us a unique view of Earth’s atmosphere. CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (Calipso) are undergoing final preparations for launch from Vandenberg Air Force Base, Calif.

CloudSat and Calipso will provide a new, 3-D perspective on Earth’s clouds and airborne particles called aerosols. The satellites will answer questions about how clouds and aerosols form, evolve and affect water supply, climate, weather and air quality.

CloudSat and Calipso employ revolutionary tools that will probe Earth’s atmosphere. Each spacecraft carries an “active” instrument that transmits pulses of energy and measures the portion of the pulses scattered back to the instrument.

CloudSat’s cloud-profiling radar is more than 1,000 times more sensitive than typical weather radar. It can detect clouds and distinguish between cloud particles and precipitation. “The new information from CloudSat will answer basic questions about how rain and snow are produced by clouds, how rain and snow are distributed worldwide and how clouds affect the Earth’s climate,” said Dr. Graeme Stephens, CloudSat principal investigator at Colorado State University, Fort Collins, Colo.

Calipso’s polarization lidar instrument can detect aerosol particles and can distinguish between aerosol and cloud particles. “With the high resolution observation that Calipso will provide, we will get a better understanding of aerosol transport and how our climate system works,” said Dr. David Winker, Calipso principal investigator at NASA’s Langley Research Center, Hampton, Va.

The satellites will be launched into a 705-kilometer (438-mile) circular, sun-synchronous polar orbit, where they will fly in formation just 15 seconds apart as members of NASA’s “A-Train” constellation with three other Earth Observing System satellites. The A-Train includes NASA’s Aqua and Aura satellites and France’s Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with observations from a Lidar satellite.

The usefulness of data from CloudSat, Calipso and the other A-Train satellites will be much greater when combined. The combined set of measurements will provide new insight into the global distribution and evolution of clouds that will lead to improvements in weather forecasting and climate prediction.

CloudSat is managed by NASA’s Jet Propulsion Laboratory, Pasadena, Calif. The radar instrument was developed at JPL, with hardware contributions from the Canadian Space Agency. Colorado State University provides scientific leadership and science data processing and distribution.

Other contributions include resources from the U.S. Air Force and the U.S. Department of Energy. Ball Aerospace and Technologies Corp. designed and built the spacecraft. A host of U.S. and international universities and research centers provides support to the science team. Some of these activities are contributed as partnerships with the project.

Calipso was developed through collaboration between NASA and the French Space Agency, Centre National d’Etudes Spatiales. NASA’s Langley Research Center leads the Calipso mission and provides science team leadership, systems engineering, payload mission operations, and validation, processing and archiving of data. Langley also developed the lidar instrument in collaboration with the Ball Aerospace and Technologies Corp., which developed the onboard visible camera.

NASA’s Goddard Space Flight Center, Greenbelt, Md., provides project management, system engineering support and overall program management. Centre National d’Etudes Spatiales provides a Proteus spacecraft developed by Alcatel, the imaging infrared radiometer, payload-to-spacecraft integration and spacecraft mission operations. The Institut Pierre Simon Laplace in Paris provides the imaging infrared radiometer science oversight, data validation and archival. Hampton University provides scientific contributions and manages the outreach program.

For more information on CloudSat and Calipso on the Internet, please visit http://www.nasa.gov/cloudsat and http://www.nasa.gov/calipso .

Original Source: NASA News Release

Bruce Fegley examines a meteorite. Image credit: WUSTL Click to enlarge
Using primitive meteorites called chondrites as their models, earth and planetary scientists at Washington University in St. Louis have performed outgassing calculations and shown that the early Earth’s atmosphere was a reducing one, chock full of methane, ammonia, hydrogen and water vapor.

In making this discovery Bruce Fegley, Ph.D., Washington University professor of earth and planetary sciences in Arts & Sciences, and Laura Schaefer, laboratory assistant, reinvigorate one of the most famous and controversial theories on the origins of life, the 1953 Miller-Urey experiment, which yielded organic compounds necessary to evolve organisms.

Chondrites are relatively unaltered samples of material from the solar nebula, According to Fegley, who heads the University’s Planetary Chemistry Laboratory, scientists have long believed them to be the building blocks of the planets. However, no one has ever determined what kind of atmosphere a primitive chondritic planet would generate.

“We assume that the planets formed out of chondritic material, and we sectioned up the planet into layers, and we used the composition of the mix of meteorites to calculate the gases that would have evolved from each of those layers,” said Schaefer. “We found a very reducing atmosphere for most meteorite mixes, so there is a lot of methane and ammonia.”

In a reducing atmosphere, hydrogen is present but oxygen is absent. For the Miller-Urey experiment to work, a reducing atmosphere is a must. An oxidizing atmosphere makes producing organic compounds impossible. Yet, a major contingent of geologists believe that a hydrogen-poor, carbon dioxide-rich atmosphere existed because they use modern volcanic gases as models for the early atmosphere. Volcanic gases are rich in water, carbon dioxide, and sulfur dioxide but contain no ammonia or methane.

“Geologists dispute the Miller-Urey scenario, but what they seem to be forgetting is that when you assemble the Earth out of chondrites, you’ve got slightly different gases being evolved from heating up all these materials that have assembled to form the Earth. Our calculations provide a natural explanation for getting this reducing atmosphere,” said Fegley.

Schaefer presented the findings at the annual meeting of the Division of Planetary Sciences of the American Astronomical Society, held Sept. 4-9 in Cambridge, England.

Schaefer and Fegley looked at different types of chondrites that earth and planetary scientists believe were instrumental in making the Earth. They used sophisticated computer codes for chemical equilibrium to figure out what happens when the minerals in the meteorites are heated up and react with each other. For example, when calcium carbonate is heated up and decomposed, it forms carbon dioxide gas.

“Different compounds in the chondritic Earth decompose when they’re heated up, and they release gas that formed the earliest Earth atmosphere,” Fegley said.

The Miller-Urey experiment featured an apparatus into which was placed a reducing gas atmosphere thought to exist on the early Earth. The mix was heated up and given an electrical charge and simple organic molecules were formed. While the experiment has been debated from the start, no one had done calculations to predict the early Earth atmosphere.

“I think these computations hadn’t been done before because they’re very difficult; we use a special code” said Fegley, whose work with Schaefer on the outgassing of Io, Jupiter’s largest moon and the most volcanic body in the solar system, served as inspiration for the present early Earth atmosphere work.

Original Source: WUSTL News Release

Ozone forecast for 1 September. Image credit: KNMI/ESA Click to enlarge
This season’s Antarctic ozone hole has swollen to an area of ten million square kilometres from mid-August – approximately the same size as Europe and still expanding. It is expected to reach maximum extent during September, and ESA satellites are vital for monitoring its development.

This year’s hole is large for this time of year, based on results from the last decade: only the ozone holes of 1996 and 2000 had a larger area at this point in their development.

Envisat’s Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) routinely monitors ozone levels on a global basis, continuing a dataset of measurements stretching back to mid-1995, previously made by the Global Ozone Monitoring Experiment (GOME) aboard the earlier ESA spacecraft ERS-2.

ESA data form the basis of an operational near-real time ozone monitoring and forecasting service forming part of the PROMOTE (PROtocol MOniToring for the GMES Service Element) consortium, made up of more than 30 partners from 11 countries, including the Royal Dutch Meteorological Institute (KNMI).

As part of the PROMOTE service, the satellite results are combined with meteorological data and wind field models so that robust ozone and ultraviolet forecasts can be made. In a first for ESA, these results are being used by the World Meteorological Organisation (WMO) to compile their regularly-updated Antarctic Ozone Bulletin.

The precise time and range of Antarctic ozone hole occurrences are determined by regional meteorological variations. During the southern hemisphere winter, the atmospheric mass above the Antarctic continent is kept cut off from exchanges with mid-latitude air by prevailing winds known as the polar vortex. This leads to very low temperatures, and in the cold and continuous darkness of this season, polar stratospheric clouds are formed that contain chlorine.

The stratospheric ozone layer that protects life on Earth from harmful ultraviolet (UV) radiation is vulnerable to the presence of certain chemicals in the atmosphere such as chlorine, originating from man-made pollutants like chlorofluorocarbons (CFCs).

Now banned under the Montreal Protocol, CFCs were once widely used in aerosol cans and refrigerators. CFCs themselves are inert, but ultraviolet radiation high in the atmosphere breaks them down into their constituent parts, which can be highly reactive with ozone.

As the polar spring arrives, the combination of returning sunlight and the presence of polar stratospheric clouds leads to splitting of chlorine into highly ozone-reactive radicals that break ozone down into individual oxygen molecules. A single molecule of chlorine has the potential to break down thousands of molecules of ozone.

The PROMOTE atmospheric ozone forecast seen here has atmospheric ozone measured in Dobson Units (DUs), which stands for the total thickness of ozone in a given vertical column if it were concentrated into a single slab at standard temperature and atmospheric pressure ? 400 DUs is equivalent to a thickness of four millimetres, for example.

Developing out of the successful precursor Tropospheric Emission Monitoring Information Service (TEMIS), PROMOTE is a portfolio of information services covering the atmosphere part of the Earth System, operating as part of ESA’s initial Services Element of Global Monitoring for Environment and Security (GMES). This is a joint initiative between ESA and the European Commission to combine all available ground- and space-based information sources and develop a global environmental monitoring capability for Europe.

Original Source: ESA Portal

Earth. Image credit: NASA Click to enlarge
Scientists have ended a long debate by proving that Earth’s core rotates faster than its surface.

Their research measured differences in the time it took seismic waves generated by nearly identical earthquakes to travel through Earth’s inner core.

According to geologists Jian Zhang of the Lamont-Doherty Earth Observatory (LDEO), Xiaodong Song of the University of Illinois at Urbana-Champaign and other co-authors of a paper in the Aug. 26 issue of the journal Science, Earth’s iron core is rotating approximately 1 degree per year faster than the rest of the planet.

“Whether the Earth’s core spins faster than its surface has been a hotly debated topic,” says Robin Reichlin, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research. “These new observations provide compelling support that it does.”

The scientists studied waveform doublets–earthquakes that are detected at the same seismic recording station in two different places, at two different times. A Sept. 2003, earthquake in the Atlantic Ocean near the South Sandwich Islands that was also detected in Ala., provided a near-exact match with one that had occurred in Dec.1993.

The seismograms were almost identical for shocks that had traveled only in the mantle and outer core. But seismic waves that had traveled through the inner core looked slightly different: they had made the trip through the Earth faster in 2003 than in 1993.

“The similar seismic waves that passed through the inner core show changes in travel times,” says Song. “The only plausible explanation is the faster rotation of the inner core.”

In all, the geologists analyzed 18 “doublets” from the South Sandwich Islands that were detected at Ala. seismic stations between 1961 and 2004.

“For decades, people thought of the Earth’s interior as changing very slowly over millions of years,” said scientist Paul Richards of LDEO, a co-author of the paper. “These results show that we live on a remarkably dynamic planet. They also underscore the fact that we know more about the moon than we know about what’s beneath our feet. Now we need to understand what is driving this difference.”

In addition to Zhang, Song and Richards, co-authors of the paper are Illinois graduate students Yingchun Li and Xinlei Sun and research scientist Felix Waldhauser. The work was also funded by the Natural Science Foundation of China.

Original Source: NSF News Release

Western Hemisphere. Image credit: NASA Click to enlarge
Scientists at the National Center for Atmospheric Research (NCAR) have created a computer simulation showing Earth’s climate in unprecedented detail at the time of the greatest mass extinction in the planet’s history. The work gives support to a theory that an abrupt and dramatic rise in atmospheric levels of carbon dioxide triggered the massive die-off 251 million years ago. The research appears in the September issue of Geology.

“The results demonstrate how rapidly rising temperatures in the atmosphere can affect ocean circulation, cutting off oxygen to lower depths and extinguishing most life,” says NCAR scientist Jeffrey Kiehl, the lead author.

Kiehl and coauthor Christine Shields focused on the dramatic events at the end of the Permian Era, when an estimated 90 to 95% of all marine species, as well as about 70% of all terrestrial species, became extinct. At the time of the event, higher-latitude temperatures were

18 to 54 degrees Fahrenheit (10 to 30 degrees Celsius) higher than today, and extensive volcanic activity had released large amounts of carbon dioxide and sulfur dioxide into the atmosphere over a 700,000-year period.

To solve the puzzle of how those conditions may have affected climate and life around the globe, the researchers turned to the Community Climate System Model (CCSM). One of the world’s premier climate research tools, the model can integrate changes in atmospheric temperatures with ocean temperatures and currents. Research teams had previously studied the Permian extinction with more limited computer models that focused on a single component of Earth’s climate system, such as the ocean.

The CCSM indicated that ocean waters warmed significantly at higher latitudes because of rising atmospheric levels of carbon dioxide (CO2), a greenhouse gas. The warming reached a depth of about 10,000 feet (4,000 meters), interfering with the normal circulation process in which colder surface water descends, taking oxygen and nutrients deep into the ocean.

As a result, ocean waters became stratified with little oxygen, a condition that proved deadly to marine life. This in turn accelerated the warming, since marine organisms were no longer removing carbon dioxide from the atmosphere.

“The implication of our study is that elevated CO2 is sufficient to lead to inhospitable conditions for marine life and excessively high temperatures over land would contribute to the demise of terrestrial life,” the authors concluded in the article.

The CCSM’s simulations showed that ocean circulation was even more stagnant than previously thought. In addition, the research demonstrated the extent to which computer models can successfully simulate past climate events. The CCSM appeared to correctly capture key details of the late Permian, including increased ocean salinity and sea surface temperatures in the high latitudes that paleontologists believe were 14 degrees Fahrenheit (8 degrees Celsius) higher than present.

The modeling presented unique challenges because of limited data and significant geographic differences between the Permian and present-day Earth. The researchers had to estimate such variables as the chemical composition of the atmosphere, the amount of sunlight reflected by Earth’s surface back into the atmosphere, and the movement of heat and salinity in the oceans at a time when all the continents were consolidated into the giant land mass known as Pangaea.

“These results demonstrate the importance of treating Earth’s climate as a system involving physical, chemical , and biological processes in the atmosphere, oceans, and land surface, all acting in an interactive manner,” says Jay Fein, director of NSF’s climate dynamics program, which funded the research. “Other studies have reached similar conclusions. What’s new here is the application of a detailed version of one of the world’s premier climate system models, the CCSM, to understand how rising levels of atmospheric carbon dioxide affected conditions in the world’s oceans and land surfaces enough to trigger a massive extinction hundreds of millions of years ago.”

Original Source: NCAR News Release

Arctic ocean. Image credit: NASA/GSFC Click to enlarge
The current warming trends in the Arctic may shove the Arctic system into a seasonally ice-free state not seen for more than one million years, according to a new report. The melting is accelerating, and a team of researchers were unable to identify any natural processes that might slow the de-icing of the Arctic.

Such substantial additional melting of Arctic glaciers and ice sheets will raise sea level worldwide, flooding the coastal areas where many of the world’s people live.

Melting sea ice has already resulted in dramatic impacts for the indigenous people and animals in the Arctic, which includes parts of Alaska, Canada, Russia, Siberia, Scandinavia and Greenland.

?What really makes the Arctic different from the rest of the non-polar world is the permanent ice in the ground, in the ocean and on land,? said lead author University of Arizona geoscientist Jonathan T. Overpeck. ?We see all of that ice melting already, and we envision that it will melt back much more dramatically in the future as we move towards this more permanent ice-free state.?

The report by Overpeck and his colleagues is published in the Aug. 23 Eos, the weekly newspaper of the American Geophysical Union. A complete list of authors and their affiliations is at the end of this release.

The report is the result of weeklong meeting of a team of interdisciplinary scientists who examined how the Arctic environment and climate interact and how that system would respond as global temperatures rise. The workshop was organized by the NSF Arctic System Science Committee, which is chaired by Overpeck. The National Science Foundation funded the meeting.

The past climates in the Arctic include glacial periods, where sea ice coverage expanded and ice sheets extended into Northern America and Europe, and warmer interglacial periods during which the ice retreats, as it has during the past 10,000 years.

By studying natural data loggers such as ice cores and marine sediments, scientists have a good idea what the ?natural envelope? for Arctic climate variations has been for the past million years, Overpeck said.

The team of scientists synthesized what is currently known about the Arctic and defined key components that make up the current system. The scientists identified how the components interact, including feedback loops that involve multiple parts of the system.

?In the past, researchers have tended to look at individual components of the Arctic,? said Overpeck. ?What we did for the first time is really look at how all of those components work together.?

The team concluded that there were two major amplifying feedbacks in the Arctic system involving the interplay between sea and land ice, ocean circulation in the North Atlantic, and the amounts of precipitation and evaporation in the system.

Such feedback loops accelerate changes in the system, Overpeck said. For example, the white surface of sea ice reflects radiation from the sun. However, as sea ice melts, more solar radiation is absorbed by the dark ocean, which heats up and results in yet more sea ice melting.

While the scientists identified one feedback loop that could slow the changes, they did not see any natural mechanism that could stop the dramatic loss of ice.

?I think probably the biggest surprise of the meeting was that no one could envision any interaction between the components that would act naturally to stop the trajectory to the new system,? Overpeck said. He added that the group investigated several possible braking mechanisms that had been previously suggested.

In addition to sea and land ice melting, Overpeck warned that permafrost?the permanently frozen layer of soil that underlies much of the Arctic?will melt and eventually disappear in some areas. Such thawing could release additional greenhouse gases stored in the permafrost for thousands of years, which would amplify human-induced climate change.

Overpeck said humans could step on the brakes by reducing carbon dioxide emissions. ?The trouble is we don?t really know where the threshold is beyond which these changes are inevitable and dangerous,” Overpeck said. ?Therefore it is really important that we try hard, and as soon as we can, to dramatically reduce such emissions.?

Original Source: University of Arizona News Release

Antarctic Snow Depth on Sea Ice. Image credit: NASA Click to enlarge
A new NASA-funded study finds that predicted increases in precipitation due to warmer air temperatures from greenhouse gas emissions may actually increase sea ice volume in the Antarctic?s Southern Ocean. This adds new evidence of potential asymmetry between the two poles, and may be an indication that climate change processes may have different impact on different areas of the globe.

“Most people have heard of climate change and how rising air temperatures are melting glaciers and sea ice in the Arctic,” said Dylan C. Powell, co-author of the paper and a doctoral candidate at the University of Maryland-Baltimore County. “However, findings from our simulations suggest a counterintuitive phenomenon. Some of the melt in the Arctic may be offset by increases in sea ice volume in the Antarctic.”

The researchers used satellite observations for the first time, specifically from the Special Sensor Microwave/Imager, to assess snow depth on sea ice, and included the satellite observations in their model. As a result, they improved prediction of precipitation rates. By incorporating satellite observations into this new method, the researchers achieved more stable and realistic precipitation data than the typically variable data found in the polar regions. The paper was published in the June issue of the American Geophysical Union’s Journal of Geophysical Research.

“On any given day, sea ice cover in the oceans of the polar regions is about the size of the U.S.,” said Thorsten Markus, co-author of the paper and a research scientist at NASA?s Goddard Space Flight Center, Greenbelt, Md. “Far-flung locations like the Arctic and Antarctic actually impact our temperature and climate where we live and work on a daily basis.”

According to Markus, the impact of the northernmost and southernmost parts on Earth on climate in other parts of the globe can be explained by thermal haline (or saline) circulation. Through this process, ocean circulation acts like a heat pump and determines our climate to a great extent. The deep and bottom water masses of the oceans make contact with the atmosphere only at high latitudes near or at the poles. In the polar regions, the water cools down and releases its salt upon freezing, a process that also makes the water heavier. The cooler, salty, water then sinks down and cycles back towards the equator. The water is then replaced by warmer water from low and moderate latitudes, and the process then begins again.

Typically, warming of the climate leads to increased melting rates of sea ice cover and increased precipitation rates. However, in the Southern Ocean, with increased precipitation rates and deeper snow, the additional load of snow becomes so heavy that it pushes the Antarctic sea ice below sea level. This results in even more and even thicker sea ice when the snow refreezes as more ice. Therefore, the paper indicates that some climate processes, like warmer air temperatures increasing the amount of sea ice, may go against what we would normally believe would occur.

“We used computer-generated simulations to get this research result. I hope that in the future we?ll be able to verify this result with real data through a long-term ice thickness measurement campaign,” said Powell. “Our goal as scientists is to collect hard data to verify what the computer model is telling us. It will be critical to know for certain whether average sea ice thickness is indeed increasing in the Antarctic as our model indicates, and to determine what environmental factors are spurring this apparent phenomenon.”

Achim Stossel of the Department of Oceanography at Texas A&M University, College Station, Tex., a third co-author on this paper, advises that “while numerical models have improved considerably over the last two decades, seemingly minor processes like the snow-to-ice conversion still need to be better incorporated in models as they can have a significant impact on the results and therefore on climate predictions.”

Original Source: NASA News Release

Artist’s impression of micro turbulence seen by Cluster. Image credit: ESA Click to enlarge
Thanks to measurements by ESA?s Cluster mission, a team of European scientists have identified ?micro?-vortices in Earth?s magnetosphere.

Such small-scale vortex turbulence, whose existence was predicted through mathematical models, has not been observed before in space. The results are not only relevant for space physics, but also for other applications like research on nuclear fusion.

On 9 March 2002, the four Cluster satellites, flying in tetrahedral formation at 100 kilometres distance from each other, were crossing the northern ?magnetic cusp? when they made their discovery. Magnetic cusps are the regions over the magnetic poles where the magnetic field lines surrounding Earth form a magnetic funnel.

The magnetic cusps are the two important regions in Earth?s magnetosphere where the ?solar wind? – a constant flow of charged particles generated by the Sun that crosses the whole Solar System – can directly access the upper layer of Earth?s atmosphere (the ionosphere).

Large amounts of plasma (a gas of charged particles) and energy are transported through these and other ?accessible? regions, to penetrate the magnetosphere – Earth?s natural protective shield. Only less than one percent of all the energy carried by the solar wind and hitting the Earth?s magnetosphere actually manages to sneak through, but it still can have a significant impact on earthly systems, like telecommunication networks and power lines.

The solar material sneaking in generates turbulence in the plasma surrounding Earth, similar to that in fluids but with more complex forces involved. Such turbulence is generated for instance in the areas of transition between layers of plasma of different density and temperature, but its formation mechanisms are not completely clear yet.

The turbulence exists at different scales, from few thousand to few kilometres across. With in situ ?multi-point? measurements, the four Cluster satellites reported in the year 2004 the existence of large scale turbulence – vortices up to 40 000 kilometres wide, at the flank of the ?magnetopause? (a boundary layer separating the magnetosphere from free space). The new discovery of ?micro? turbulence, with vortices of only 100 kilometres across, is a first in the study of the plasma surrounding Earth.

Cluster: an unprecedented diagnostic tool

Such a discovery is very relevant. For example, it allows scientists to start linking small and large-scale turbulence, and start questioning how it is actually formed and what are the connections. For instance, what are the basic mechanisms driving and shaping the turbulence? How much do vortices contribute to the transport of mass and energy through boundary layers? Are small vortices needed to generate large ones? Or, on the other hand, do large vortices dissipate their energy and create a cascade of smaller ones?

In trying to answer these questions, Cluster is an unprecedented diagnostic tool for the first three-dimensional map of the near-Earth environment, its exceptionality being given by its multi-spacecraft simultaneous observations. Cluster is revolutionising our understanding of the ways and the mechanisms by which solar activity affects Earth.

Besides, Cluster?s study of the turbulence in Earth?s plasma, with the dynamics and the energies involved, is contributing to the advancement of fundamental theories on plasma. This is not only important in astrophysics, but also as far as the understanding and the handling of plasma in laboratories is concerned, given the high energies involved. This is particularly relevant for research on nuclear fusion.

For example, Cluster?s data are complementing research on plasma physics in the international ITER project, an experimental step involving several research institutes around the world for tomorrow?s electricity-producing power plants. In this respect, by probing into the magnetosphere, Cluster has free access to the only open ?natural laboratory? for the study of plasma physics.

Original Source: ESA Portal

Looking down on Earth. Image credit: NASA Click to enlarge
A number of hypotheses have been used to explain how free oxygen first accumulated in Earth’s atmosphere some 2.4 billion years ago, but a full understanding has proven elusive. Now a new model offers plausible scenarios for how oxygen came to dominate the atmosphere, and why it took at least 300 million years after bacterial photosynthesis started producing oxygen in large quantities.

The big reason for the long delay was that processes such as volcanic gas production acted as sinks to consume free oxygen before it reached levels high enough to take over the atmosphere, said Mark Claire, a University of Washington doctoral student in astronomy and astrobiology. Free oxygen would combine with gases in a volcanic plume to form new compounds, and that process proved to be a significant oxygen sink, he said.

Another sink was iron delivered to the Earth’s outer crust by bombardment from space. Free oxygen was consumed as it oxidized, or rusted, the metal.

But Claire said that just changing the model to reflect different iron content in the outer crust makes a huge difference in when the model shows free oxygen filling the atmosphere. Increasing the actual iron content fivefold would have delayed oxygenation by more than 1 billion years, while cutting iron to one-fifth the actual level would have allowed oxygenation to happen more than 1 billion years earlier.

“We were fairly surprised that we could push the transition a billion years in either direction, because those levels of iron in the outer crust are certainly plausible given the chaotic nature of how Earth formed,” he said.

Claire and colleagues David Catling, a UW affiliate professor in atmospheric sciences, and Kevin Zahnle of the National Aeronautics and Space Administration’s Ames Research Center in California will discuss their model tomorrow (Aug. 9) in Calgary, Alberta, during the Geological Society of America’s Earth System Processes 2 meeting.

Earth’s oxygen supply originated with cyanobacteria, tiny water-dwelling organisms that survive by photosynthesis. In that process, the bacteria convert carbon dioxide and water into organic carbon and free oxygen. But Claire noted that on the early Earth, free oxygen would quickly combine with an abundant element, hydrogen or carbon for instance, to form other compounds, and so free oxygen did not build up in the atmosphere very readily. Methane, a combination of carbon and hydrogen, became a dominant atmospheric gas.

With a sun much fainter and cooler than today, methane buildup warmed the planet to the point that life could survive. But methane was so abundant that it filled the upper reaches of the atmosphere, where such compounds are very rare today. There, ultraviolet exposure caused the methane to decompose and its freed hydrogen escaped into space, Claire said.

The loss of hydrogen atoms to space allowed increasingly greater amounts of free oxygen to oxidize the crust. Over time, that slowly diminished the amount of hydrogen released from the crust by the combination of pressure and temperature that formed the rocks in the crust.

“About 2.4 billion years ago, the long-term geologic sources of oxygen outweighed the sinks in a somewhat permanent fashion,” Claire said. “Escaping to space is the only permanent escape that we envision for the hydrogen, and that drove the planet to a higher oxygen level.”

The model developed by Claire, Catling and Zahnle indicates that as hydrogen atoms stripped from methane escaped into space, greenhouse conditions caused by the methane blanket quickly collapsed. Earth’s average temperature likely cooled by about 30 degrees Celsius, or 54 degrees Fahrenheit, and oxygen was able to dominate the atmosphere because there was no longer an overabundance of hydrogen to consume the oxygen.

The work is funded by NASA’s Astrobiology Institute and the National Science Foundation’s Integrative Graduate Education and Research Traineeship program, both of which foster research to understand life in the universe by examining the limits of life on Earth.

“There is interest in this work not just to know how an oxygen atmosphere came about on Earth but to look for oxygen signatures for other Earth-like planets,” Claire said.

Original Source: UW News Release

Earth taken by MESSENGER on July, 30. Image credit: NASA Click to enlarge
NASA’s MESSENGER spacecraft, headed toward the first study of Mercury from orbit, swung by Earth today for a gravity assist that propelled it deeper into the inner solar system.

Mission operators at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md, said MESSENGER’s systems performed flawlessly. The spacecraft swooped around Earth, coming to a closest approach point of approximately 1,458 miles (2,347 kilometers) over central Mongolia at 3:13 p.m. EDT.

The spacecraft used the tug of Earth’s gravity to significantly change its trajectory. Its average orbit distance is nearly 18 million miles closer to the sun. The maneuver sent it toward Venus for another gravity-assist flyby next year.

Launched Aug. 3, 2004, from Cape Canaveral Air Force Station, Fla., the solar-powered spacecraft is approximately 581 million miles (930 million kilometers) into a 4.9 billion mile (7.9 billion kilometer) voyage that includes 14 more loops around the sun. MESSENGER will fly past Venus twice and Mercury three times before moving into orbit.

The Venus flybys in October 2006 and June 2007 will use the planet’s gravity to guide MESSENGER toward Mercury’s orbit. The Mercury flybys in January 2008, October 2008 and September 2009 will help MESSENGER match the planet’s speed. These events will set up the maneuver in March 2011 that starts a year-long science orbit around Mercury.

“This Earth flyby is the first of a number of critical mission milestones during MESSENGER’s circuitous journey toward Mercury orbit insertion,” said Sean C. Solomon, the mission’s principal investigator from the Carnegie Institution of Washington. “Not only did it help the spacecraft sharpen its aim toward our next maneuver, it presented a special opportunity to calibrate several of our science instruments.”

MESSENGER’s main camera snapped several approach shots of Earth and the moon during the past week. Today the camera is taking a series of color images, beginning with South America and continuing for one full Earth rotation. Science team members will string the images into a video documenting MESSENGER’s departure.

On Earth approach, the craft’s atmospheric and surface composition spectrometer made several scans of the moon in conjunction with the camera observations. In addition, the particle and magnetic field instruments spent several hours measuring Earth’s magnetosphere. The science team will download the data and images through NASA’s Deep Space Network over the next several weeks, continuing assessment of the instruments’ performance.

MESSENGER will conduct the first orbital study of Mercury, the least explored of the terrestrial planets that include Venus, Earth and Mars. During one Earth year (four Mercury years), MESSENGER will provide the first images of the entire planet. It will collect detailed information about the composition and structure of Mercury’s crust, its geologic history, nature of its atmosphere and magnetosphere, makeup of its core and polar materials.

MESSENGER, short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging, is the seventh mission in NASA’s Discovery Program of lower-cost scientifically focused exploration projects. APL designed, built and operates the spacecraft and manages the mission for NASA’s Science Mission Directorate.

For information about the spacecraft and mission on the Web, visit: http://messenger.jhuapl.edu

Original Source: NASA News Release