The Daily Galaxy: News from Planet Earth & Beyond |
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Posted: 21 Aug 2014 08:10 AM PDT
Superlatives are the trademark of the planet Jupiter. The magnetic field at the top edge of the cloud surrounding the largest member of the solar system is around ten times stronger than Earth’s, and is by far the largest magnetosphere around a planet in our Solar System. Just why this field has a similar structure to that of our own planet although the interiors of the two celestial objects have a completely different structure, has mystified researchers for a long time. With the aid of the most detailed computer simulations to date, a team headed by the Max Planck Institute for Solar System Research in Göttingen has now succeeded in explaining the origin of the magnetic field deep inside the gaseous giant.Jupiter autopsy: The magnetic field lines illustrate the high complexity of the magnetic field inside the planet, which, however, quickly decreases beyond the metallic layer (black line). On the surface, a dipolar part that is inclined by ten degrees with respect to the axis of rotation dominates. The thickness of the field lines is a measure of the local magnetic field strength. In the equatorial region, a jet produces bundles of field lines with a pronounced east-west orientation at the transition to the metallic layer. The colored contours represent the radial surface field. Red indicates field lines directed outwards, blue inwards; green denotes a weak field. The colour coding of the sections represents the field in the east-west direction – red indicates eastwards, blue westwards. Magnetic fields are always generated when electric currents flow. The Earth is surrounded by a magnetic field because, deep in its interior, there is a circulating molten mass of iron and nickel. This motion gives rise to electric currents that generate Earth’s familiar dipolar magnetic field, in much the same way as a bicycle dynamo operates. Physicists call it the geo-dynamo. But how does the dynamo inside of Jupiter work? Jupiter consists predominantly of hydrogen and helium. Photos of the planet show coloured bands of cloud and gigantic tornados such as the Great Red Spot. The temperature at the upper cloud boundary is minus 100 degrees Celsius, but temperature, pressure and electrical conductivity increase enormously with increasing depth. At a depth of just under 10,000 kilometres and a pressure of several million atmospheres, the hydrogen even becomes conductive like a metal – an exotic state of matter which does not exist on Earth. It is still unclear whether there is a rocky core at the centre of the planet; it could possibly amount to around 20 percent of the Jupiter radius – corresponding to 14,000 kilometres. Previous computer simulations on the formation of the magnetic field had to greatly simplify this complex structure. The upper gaseous region and the lower metallic region were treated separately, for example. Thus, no computation correctly reproduced the strength and the form of the magnetic field as determined by space probes. “Several colleagues assumed that certain physical quantities changed suddenly at the transition to the region of the metal-like conducting hydrogen,” says project leader Johannes Wicht from the Max Planck Institute for Solar System Research in Göttingen. But new models from colleagues at the University of Rostock seem to prove that this is probably not the case. The properties change gradually over the whole gas layer so that the separate treatment of the outer and inner region is hardly justified. The important step forward here was the fact that, for the first time, the Göttingen-based physicists dealt with all regions of the planet in the same simulation. To this effect, the Max Planck Society’s huge Hydra supercomputer in Garching had to spend around six months on the computation. The result was impressive: it portrayed Jupiter’s magnetic field more or less as space probes had determined it in nature. “The main part of the magnetic field, which looks so similar to Earth’s magnetic field, is generated deep inside the planet, where the properties no longer change so strongly,” says Wicht. The new simulations indicate that a second, weaker dynamo is also active, however. It operates in the transition zone to the metallic layer near the equator. It is brought about by a strong wind blowing towards the east, a so-called jet, which can be recognised from the cloud movements. In the outer, cool regions of the atmosphere it is not yet possible for a magnetic field to be generated, as the conductivity here is too low. But at greater depths the temperature rises, and from around 8,000 kilometres below the cloud cover, the electrical conductivity, thanks to the formation of plasma, is high enough for the dynamo to start. “Crucial here is the product of wind speed and electrical conductivity,” explains Moritz Heimpel from the University of Alberta in Edmonton, Canada. As soon as it exceeds a specific value, a magnetic field can form. “The jet shears the magnetic field in the east-west direction and produces a characteristic magnetic band structure in the equatorial region,” says Thomas Gastine, a staff member at the Max Planck Institute for Solar System Research. “In order to portray the special properties of the two dynamo processes involved, it was particularly important to model the interior properties of the planet as accurately as possible,” adds Lucia Duarte, who carried out the first computation during her doctoral work at the Max Planck Institute in Göttingen. Hence, two magnetic fields form, which superimpose: the Earth-like one in the deep layer of the metal-like conducting hydrogen, and the weaker band structure generated by the equatorial jet. “The Earth-like field corresponds in strength and structure to the measurement data to date provided by space probes, which do not allow the band structure to be resolved,” says Thomas Gastine. The simulations span a period of around 6,500 years and also reveal changes. The field strength should vary, for example, and the inclination of the axis should change by around 0.02 degrees per year. It will soon be possible for the Juno space probe to check this and further properties predicted by the new model. The American space craft was launched three years ago and is due to enter into an orbit around the giant planet in August 2016. “With the new measurement data, we will find out much more about the inner structure and the magnetic field than has been possible to date, and can hopefully confirm the band structures as well,” says Johannes Wicht. The Daily Galaxy via MPS |
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Posted: 20 Aug 2014 08:18 PM PDT
The first breakthrough paper to come out of a massive U.S. expedition to one of Earth’s final frontiers shows that there’s life and an active ecosystem one-half mile below the surface of the West Antarctic Ice Sheet, specifically in a lake that hasn’t seen sunlight or felt a breath of wind for millions of years. “We are looking at a water column that probably has about 4,000 things we call species. It’s incredibly diverse,” said Brent Christner, associate professor of biological sciences at Louisiana State University. The life is in the form of microorganisms that live beneath the enormous Antarctic ice sheet and convert ammonium and methane into the energy required for growth. Many of the microbes are single-celled organisms known as Archaea, said Montana State University professor John Priscu, the chief scientist of the U.S. project called WISSARD that sampled the sub-ice environment. He is also co-author of the Mpaper in the Aug. 21 issue of Nature.“We were able to prove unequivocally to the world that Antarctica is not a dead continent,” Priscu said, adding that data in the Nature paper is the first direct evidence that life is present in the subglacial environment beneath the Antarctic ice sheet. Lead author Christner said, “It’s the first definitive evidence that there’s not only life, but active ecosystems underneath the Antarctic ice sheet, something that we have been guessing about for decades. With this paper, we pound the table and say, ‘Yes, we were right.’” Priscu said he wasn’t entirely surprised that the team found life after drilling through half a mile of ice to reach Subglacial Lake Whillans in January 2013. An internationally renowned polar biologist, Priscu researches both the South and North Poles. This fall will be his 30th field season in Antarctica, and he has long predicted the discovery. More than a decade ago, he published two manuscripts in the journal Science describing for the first time that microbial life can thrive in and under Antarctic ice. Five years ago, he published a manuscript where he predicted that the Antarctic subglacial environment would be the planet’s largest wetland, one not dominated by the red-winged blackbirds and cattails of typical wetland regions in North America, but by microorganisms that mine minerals in rocks at subzero temperatures to obtain the energy that fuels their growth. Following more than a decade of traveling the world presenting lectures describing what may lie beneath Antarctic ice, Priscu was instrumental in convincing U.S. national funding agencies that this research would transform the way we view the fifth largest continent on the planet. Although he was not really surprised about the discovery, Priscu said he was excited by some of the details of the Antarctic find, particularly how the microbes function without sunlight at subzero temperatures and the fact that evidence from DNA sequencing revealed that the dominant organisms are archaea. Archaea is one of three domains of life, with the others being Bacteria and Eukaryote. Many of the subglacial archaea use the energy in the chemical bonds of ammonium to fix carbon dioxide and drive other metabolic processes. Another group of microorganisms uses the energy and carbon in methane to make a living. According to Priscu, the source of the ammonium and methane is most likely from the breakdown of organic matter that was deposited in the area hundreds of thousands of years ago when Antarctica was warmer and the sea inundated West Antarctica. He also noted that, as Antarctica continues to warm, vast amounts of methane, a potent greenhouse gas, will be liberated into the atmosphere enhancing climate warming. The U.S. team also proved that the microorganisms originated in Lake Whillans and weren’t introduced by contaminated equipment, Priscu said. Skeptics of his previous studies of Antarctic ice have suggested that his group didn’t actually discover microorganisms, but recovered microbes they brought in themselves. “We went to great extremes to ensure that we did not contaminate one of the most pristine environments on our planet while at the same time ensuring that our samples were of the highest integrity,” Priscu said. Extensive tests were conducted two years ago on WISSARD’s borehole decontamination system to ensure that it worked, and Priscu led a publication in an international journal presenting results of these tests. This decontamination system was mated to a one-of-a-kind hot water drill that was used to melt a borehole through the ice sheet, which provided a conduit to the subglacial environment for sampling. Every day in Antarctica, he would tell his team to keep it simple, Priscu said. To prove that an ecosystem existed below the West Antarctic Ice Sheet, he wanted at least three lines of evidence. They had to see microorganisms under the microscope that came from Lake Whillans and not contaminated equipment. They then had to show that the microorganisms were alive and growing. They had to be identifiable by their DNA. When the team found those things, he knew they had succeeded, Priscu said. The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project officially began in 2009 with a $10 million grant from the National Science Foundation. Now involving 13 principal investigators at eight U.S. institutions, the researchers drilled down to Subglacial Lake Whillans in January 2013. The microorganisms they discovered are still being analyzed at MSU and other collaborating institutions. Planning to drill again this austral summer in a new Antarctic location, Priscu said WISSARD was the first large-scale multidisciplinary effort to directly examine the biology of an Antarctic subglacial environment. The Antarctic Ice Sheet covers an area 1 ½ times the size of the United States and contains 70 percent of Earth's freshwater, and any significant melting can drastically increase sea level. Lake Whillans, one of more than 200 known lakes beneath the Antarctic Ice Sheet and the primary lake in the WISSARD study, fills and drains about every three years. The river that drains Lake Whillans flows under the Ross Ice Shelf, which is the size of France, and feeds the Southern Ocean, where it can provide nutrients for life and influence water circulation patterns. The opportunity to explore the world under the West Antarctic Ice Sheet is an unparalleled opportunity for the U.S. team, as well as for several MSU-affiliated researchers who are part of that team and wrote or co-authored the Nature paper, Priscu said. The fact that MSU was so involved reflects the fact that it is pioneering a new field of science, Priscu said. MSU is the common ancestor of many scientists who study life in and under ice. “I always tell my students when they come into the lab that ‘We are inventing this field of science. It’s working on life in ice and under ice. This field has never existed before. We thought it up. You are pioneers,’” Priscu said. Appreciative of the opportunity to participate in WISSARD, Vick-Majors said she saw bacteria under the microscope within an hour after the first sample of water was pulled out of Subglacial Lake Whillans. Within days, she saw proof that the bacteria were active. “It was very exciting. It will be hard to top,” she said. She added that, “If you want to do microbial ecology in Antarctic subglacial environments, John is probably the person you want to work with. I feel very lucky to have gotten the opportunity.” Agreeing, Michaud said, “Some of the graduate students joke, ‘How do we top this?’ We can’t.” But the students can build on their WISSARD experience and gain a deeper understanding of Subglacial Lake Whillans and other subglacial habitats, he said. It’s not about going out and finding more novel habitats. Christner said the team that wrote the paper in Nature is the dream team of polar biology. Besides the MSU-affiliated scientists, the co-authors include Amanda Achberger, a graduate student at Louisiana State University; Carlo Barbante, a geochemist at the University of Venice in Italy; Sasha Carter, a postdoctoral researcher at the University of California in San Diego; and Knut Christianson a postdoctoral researcher from St. Olaf College in Minnesota and New York University. The Daily Galaxy via Montana State University |
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