Tech & Science
Technology and Science news from Boulder, Colorado
CU: Early life on Earth supported by faint sun
Jul 21st
In fact, two CU-Boulder researchers say all that may have been required to sustain liquid water and primitive life on Earth during the Archean eon 2.8 billion years ago were reasonable atmospheric carbon dioxide amounts believed to be present at the time and perhaps a dash of methane. The key to the solution was the use of sophisticated three-dimensional climate models that were run for thousands of hours on CU’s Janus supercomputer, rather than crude, one-dimensional models used by almost all scientists attempting to solve the paradox, said doctoral student Eric Wolf, lead study author.
“It’s really not that hard in a three-dimensional climate model to get average surface temperatures during the Archean that are in fact moderate,” said Wolf, a doctoral student in CU-Boulder’s atmospheric and oceanic sciences department. “Our models indicate the Archean climate may have been similar to our present climate, perhaps a little cooler. Even if Earth was sliding in and out of glacial periods back then, there still would have been a large amount of liquid water in equatorial regions, just like today.”
Evolutionary biologists believe life arose on Earth as simple cells roughly 3.5 billion years ago, about a billion years after the planet is thought to have formed. Scientists have speculated the first life may have evolved in shallow tide pools, freshwater ponds, freshwater or deep-sea hydrothermal vents, or even arrived on objects from space.
A cover article by Wolf and Toon on the topic appears in the July issue of Astrobiology. The study was funded by two NASA grants and by the National Science Foundation, which supports CU-Boulder’s Janus supercomputer used for the study.
Scientists have been trying to solve the faint young sun paradox since 1972, when Cornell University scientist Carl Sagan — Toon’s doctoral adviser at the time — and colleague George Mullen broached the subject. Since then there have been many studies using 1-D climate models to try to solve the faint young sun paradox — with results ranging from a hot, tropical Earth to a “snowball Earth” with runaway glaciation — none of which have conclusively resolved the problem.
“In our opinion, the one-dimensional models of early Earth created by scientists to solve this paradox are too simple — they are essentially taking the early Earth and reducing it to a single column atmospheric profile,” said Toon. “One-dimensional models are simply too crude to give an accurate picture.”
Wolf and Toon used a general circulation model known as the Community Atmospheric Model version 3.0 developed by the National Center for Atmospheric Research in Boulder and which contains 3-D atmosphere, ocean, land, cloud and sea ice components. The two researchers also “tuned up” the model with a sophisticated radiative transfer component that allowed for the absorption, emission and scattering of solar energy and an accurate calculation of the greenhouse effect for the unusual atmosphere of early Earth, where there was no oxygen and no ozone, but lots of CO2 and possibly methane.
The simplest solution to the faint sun paradox, which duplicates Earth’s present climate, involves maintaining roughly 20,000 parts per million of the greenhouse gas CO2 and 1,000 ppm of methane in the ancient atmosphere some 2.8 billion years ago, said Wolf. While that may seem like a lot compared to today’s 400 ppm of CO2 in the atmosphere, geological studies of ancient soil samples support the idea that CO2 likely could have been that high during that time period. Methane is considered to be at least 20 times more powerful as a greenhouse gas than CO2 and could have played a significant role in warming the early Earth as well, said the CU researchers.
There are other reasons to believe that CO2 was much higher in the Archean, said Toon, who along with Wolf is associated with CU’s Laboratory for Atmospheric and Space Physics. The continental area of Earth was smaller back then so there was less weathering of the land and a lower release of minerals to the oceans. As a result there was a smaller conversion of CO2 to limestone in the ocean. Likewise, there were no “rooted” land plants in the Archean, which could have accelerated the weathering of the soils and indirectly lowered the atmospheric abundance of CO2, Toon said.
Another solution to achieving a habitable but slightly cooler climate under the faint sun conditions is for the Archean atmosphere to have contained roughly 15,000 to 20,000 ppm of CO2 and no methane, said Wolf. “Our results indicate that a weak version of the faint young sun paradox, requiring only that some portion of the planet’s surface maintain liquid water, may be resolved with moderate greenhouse gas inventories,” the authors wrote in Astrobiology.
“Even if half of Earth’s surface was below freezing back in the Archean and half was above freezing, it still would have constituted a habitable planet since at least 50 percent of the ocean would have remained open,” said Wolf. “Most scientists have not considered that there might have been a middle ground for the climate of the Archean.
“The leap from one-dimensional to three-dimensional models is an important step,” said Wolf. “Clouds and sea ice are critical factors in determining climate, but the one-dimensional models completely ignore them.”
Has the faint young sun paradox finally been solved? “I don’t want to be presumptuous here,” said Wolf. “But we show that the paradox is definitely not as challenging as was believed over the past 40 years. While we can’t say definitively what the atmosphere looked like back then without more geological evidence, it is certainly not a stretch at all with our model to get a warm early Earth that would have been hospitable to life.”
“The Janus supercomputer has been a tremendous addition to the campus, and this early Earth climate modeling project would have impossible without it,” said Toon. The researchers estimated the project required roughly 6,000 hours of supercomputer computation time, an effort equal to about 10 years on a home computer.
-CU-
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CU-Boulder study: Spiral galaxies like Milky Way bigger than thought
Jun 27th
CU-Boulder Professor John Stocke, study leader, said new observations with Hubble’s $70 million Cosmic Origins Spectrograph, or COS, designed by CU-Boulder show that normal spiral galaxies are surrounded by halos of gas that can extend to over 1 million light-years in diameter. The current estimated diameter of the Milky Way, for example, is about 100,000 light-years. One light-year is roughly 6 trillion miles.
The material for galaxy halos detected by the CU-Boulder team originally was ejected from galaxies by exploding stars known as supernovae, a product of the star formation process, said Stocke of CU-Boulder’s astrophysical and planetary sciences department. “This gas is stored and then recycled through an extended galaxy halo, falling back onto the galaxies to reinvigorate a new generation of star formation,” he said. “In many ways this is the ‘missing link’ in galaxy evolution that we need to understand in detail in order to have a complete picture of the process.”
Stocke gave a presentation on the research June 27 at the University of Edinburgh’s Higgs Centre for Theoretical Physics in Scotland at a conference titled “Intergalactic Interactions.” The CU-Boulder research team also included professors Michael Shull and James Green and research associates Brian Keeney, Charles Danforth, David Syphers and Cynthia Froning, as well as University of Wisconsin-Madison Professor Blair Savage.
Building on earlier studies identifying oxygen-rich gas clouds around spiral galaxies by scientists at the Space Telescope Science Institute in Baltimore, the University of Massachusetts, Amherst College and the University of California, Santa Cruz, Stocke and his colleagues determined that such clouds contain almost as much mass as all the stars in their respective galaxies. “This was a big surprise,” said Stocke. “The new findings have significant consequences for how spiral galaxies change over time.”
In addition, the CU-Boulder team discovered giant reservoirs of gas estimated to be millions of degrees Fahrenheit that were enshrouding the spiral galaxies and halos under study. The halos of the spiral galaxies were relatively cool by comparison — just tens of thousands of degrees — said Stocke, also a member of CU-Boulder’s Center for Astrophysics and Space Astronomy, or CASA.
Shull, a professor in CU-Boulder’s astrophysical and planetary sciences department and a member of CASA, emphasized that the study of such “circumgalactic” gas is in its infancy. “But given the expected lifetime of COS on Hubble, perhaps another five years, it should be possible to confirm these early detections, elaborate on the results and scan other spiral galaxies in the universe,” he said.
Prior to the installation of COS on Hubble during NASA’s final servicing mission in May 2009, theoretical studies showed that spiral galaxies should possess about five times more gas than was being detected by astronomers. The new observations with the extremely sensitive COS are now much more in line with the theories, said Stocke.
The CU-Boulder team used distant quasars — the swirling centers of supermassive black holes — as “flashlights” to track ultraviolet light as it passed through the extended gas haloes of foreground galaxies, said Stocke. The light absorbed by the gas was broken down by the spectrograph, much like a prism does, into characteristic color “fingerprints” that revealed temperatures, densities, velocities, distances and chemical compositions of the gas clouds.
“This gas is way too diffuse to allow its detection by direct imaging, so spectroscopy is the way to go,” said Stocke. CU-Boulder’s Green led the design team for COS, which was built by Ball Aerospace & Technologies Corp. of Boulder for NASA.
While astronomers hope the Hubble Space Telescope keeps on chugging for years to come, there will be no more servicing missions. And the James Webb Space Telescope, touted to be Hubble’s successor beginning in late 2018, has no UV light-gathering capabilities, which will prevent astronomers from undertaking studies like those done with COS, said Green.
“Once Hubble ceases to function, we will lose the capability to study galaxy halos for perhaps a full generation of astronomers,” said Stocke. “But for now, we are fortunate to have both Hubble and its Cosmic Origins Spectrograph to help us answer some of the most pressing issues in cosmology.”
The study was supported by a NASA/Hubble Space Telescope contract to the Cosmic Origins Spectrograph science team, general NASA/Hubble Space Telescope observing grants to Stocke and a National Science Foundation grant to Keeney.
-CU-
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CU joins Sloan Digital Sky Survey to map stars, galaxies and quasars in 3D
Jun 26th
The survey, known as SDSS-IV, is the fourth stage of an effort that began with SDSS-I in 2000 to create the largest digital color image of the northern sky, said CU-Boulder Professor Michael Shull of the astrophysical and planetary sciences department, lead scientist in the effort by CU-Boulder to join the survey. Since 2000, astronomers have mapped about one-half of the visible northern sky in three dimensions as part of the three prior Sloan sky surveys, discovering nearly half a billion astronomical objects ranging from asteroids and stars to galaxies and distant quasars in the process.
“We got into this because we think it is going to be a great recruitment tool for new students, and we have one of the best undergraduate majors in the country,” Shull said. “We also want to recruit high-caliber graduate students and postdoctoral researchers.”
The SDSS 2.5-meter telescope is located at the Apache Point Observatory in Sunspot, N.M., and is owned by the Astrophysical Research Consortium, or ARC, an organization of eight research institutions including CU-Boulder. The Sloan telescope sky-mapping project is funded by the Alfred P. Sloan Foundation, the participating institutions, the National Science Foundation and the U.S. Department of Energy Office of Science. Apache Point also hosts several other telescopes, including a 3.5-meter optical telescope owned and operated by ARC and routinely used by CU-Boulder.
ARC was formed in 1984 to create a national observatory that could provide telescope time to each member university based on its investment. Current ARC members in addition to CU-Boulder are the University of Chicago, Johns Hopkins University, Princeton University, the Institute of Advanced Study in Princeton, N.J., the University of Washington, the University of Virginia and New Mexico State University. CU-Boulder owns a one-eighth share of each of the two telescopes.
The costs to build new instruments, make observations and analyze data from the SDSS-IV from 2014 to 2020 is estimated to be between $50 million and $60 million, said Shull. The Sloan Foundation is contributing roughly $10 million, while additional funds are coming from more than 10 full institutional members, including CU, and from scientists with individual and small group memberships from various institutions.
Full institutional partners like CU-Boulder are paying roughly $1 million to join part four of the Sloan sky survey effort. CU-Boulder’s member fee was supported by university grants, awards, donations, general funds and indirect cost recovery savings. As an early institutional partner joining the Sloan IV survey before the end of the current fiscal year, CU received a $350,000 discount from ARC, said Shull.
Light from the Sloan telescope is directed to two powerful new instruments — a dual-channel visible light, or optical spectrograph, and a near-infrared spectrograph. Astronomical spectrographs break light into telltale colors much like a prism, revealing information about the size, temperature, composition and motion of celestial objects, said Shull.
The Sloan spectrographs will carry out a massive survey of galaxies and quasars in the distant universe, as well as stars in the Milky Way and thousands of nearby galaxies, said Shull, who also is a member of CU-Boulder’s Center for Astrophysics and Space Astronomy.
The new optical spectrograph on the Sloan telescope can take data from up to 1,000 galaxies or quasars simultaneously, he said. The instrument includes a circular aluminum plate roughly the size of a large pizza pan with 1,000 small perforations precisely drilled to match up with known astronomical objects in the sky. Each hole is plugged with an optical fiber attached to the spectrograph.
“I think this is going to be a perfect way for undergraduates to get their hands dirty working with ‘big data,’ said Shull. “A lot of undergraduates are better at computers than we are, so hiring a freshman or a sophomore who really wants to get into computing and big data sets in the field of astronomy is one of our goals.”
One of the biggest discoveries by SDSS-III astronomers came in 2012 when they detected the predicted signature of the first sound waves from matter and radiation in the early universe, said Shull. Sloan researchers used a multi-fiber spectrograph as part of the Baryon Oscillation Sky Survey, or BOSS, to detect the large-scale structures of ancient galaxies — similar in some ways to ripples on a pond — that were preserved after the Big Bang.
Shull, who plans to use the multi-fiber spectrograph to hunt for distant quasars in the early universe going back 13 million years, said the BOSS effort also is expected to reveal new information about so-called “dark energy.” A hypothetical form of energy that makes up the majority of the universe and produces a force that opposes gravity, dark energy is thought to be the cause of the accelerating expansion of the universe.
Another SDSS-IV effort will be a sky survey in the infrared to probe the distribution, dynamics and chemistry of stars and to explore the formation of our Milky Way Galaxy and its two companion galaxies, the Large Magellanic Cloud and the Small Magellanic Cloud, said Shull. Since the two Magellanic Clouds are best viewed from the southern hemisphere, SDSS scientists plan to collaborate with astronomers who are using the 2.5 meter du Pont Telescope at Las Campanas, Chile, on the effort.
SDSS-IV astronomers also will be using the BOSS instrument to study the internal structure of 10,000 nearby galaxies. The data will include precise velocities of stellar motions and chemical abundances for a large range of galaxy masses, types and environments. The data will complement observations of two newly completed American telescopes: the ALMA millimeter and submillimeter array radio telescope in Chile and the Expanded-Very Large Array radio telescope in New Mexico.
SDSS-IV also has had a significant citizen science component since 2007, when a data set of a million galaxies was released to the public, who were asked to classify them in three categories: Elliptical galaxies, merging galaxies and spiral galaxies, including the direction of the spiral arms. An astounding 70,000 classifications were received by SDSS scientists from the public within an hour of the data release, and during the first year more than 150,000 people made more than 50 million galaxy classifications.
CU has a legacy in space dating back nearly 70 years, said CU-Boulder Vice Chancellor for Research Stein Sture. It is the top funded public university by NASA, has a $70 million instrument now flying on the Hubble Space Telescope, is leading a $485 million mission to Mars and controls four NASA satellites from campus.
A video news story on the project is available at http://youtu.be/1Rke59L5cAo.
-CU-
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