Tuesday, May 31, 2011

Relevant Planetary Research

Another interesting article from Science Daily.com


Mars: Red Planet's Rapid Formation Explains Its Small Size Relative to Earth

ScienceDaily (May 30, 2011) — Mars developed in as little as two to four million years after the birth of the solar system, far more quickly than Earth, according to a new study published in the May 26 issue of the journal Nature. The red planet's rapid formation helps explain why it is so small, say the study's co-authors, Nicolas Dauphas at the University of Chicago and Ali Pourmand at the University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science.
Mars probably is not a terrestrial planet like Earth, which grew to its full size over 50 to 100 million years via collisions with other small bodies in the solar system, said Dauphas, an associate professor in geophysical sciences.
"Earth was made of embryos like Mars, but Mars is a stranded planetary embryo that never collided with other embryos to make an Earthlike planet," Dauphas said. The new work provides supporting evidence for this idea, which was first proposed 20 years ago on the basis of planetary growth simulations.
The new evidence likely will change the way planetary scientists view Mars, observed Pourmand, assistant professor in marine geology and geophysics at the UM Rosenstiel School. "We thought that there were no embryos in the solar system to study, but when we study Mars, we are studying embryos that eventually made planets like Earth."
There had been large uncertainties in the formation history of Mars because of the unknown composition of its mantle, the rock layer that underlies the crust. "Now we can shrink those uncertainties to the point where we can do interesting science," Dauphas said.
Hafnium-tungsten chronometer
Dauphas and Pourmand were able to refine the age of Mars by using the radioactive decay of hafnium to tungsten in meteorites as a chronometer. Hafnium 182 decays into tungsten 182 in a half-life of nine million years. This relatively rapid decay process means that almost all hafnium 182 will disappear in 50 million years, providing a way to assemble a fine-scale chronology of early events in the solar system.
"To apply that system you need two gradients," Pourmand explained. "You need the hafnium-tungsten ratio of the mantle of Mars and you need the tungsten isotopic composition of the mantle of Mars." The latter was well known from analyses of martian meteorites, but not the former.
Previous estimates of the formation of Mars ranged as high as 15 million years because the chemical composition of the martian mantle was largely unknown. Scientists still wrestle with large uncertainties in the composition of Earth's mantle because of composition-altering processes such as melting.
"We have the same problem for Mars," Dauphas said. Analyses of martian meteorites provide clues as to the mantle composition of Mars, but their compositions also have changed.
Solving some lingering unknowns regarding the composition of chondrites, a common type of meteorites, provided the data they needed. As essentially unaltered debris left over from the birth of the solar system, chondrites serve as a Rosetta stone for deducing planetary chemical composition.
Cosmochemists have intensively studied chondrites, but still poorly understand the abundances of two categories of elements that they contained, including uranium, thorium, lutetium and hafnium.
Dauphas and Pourmand thus analyzed the abundances of these elements in more than 30 chondrites, and compared those to the compositions of another 20 martian meteorites.
"Once you solve the composition of chondrites you can address many other questions," Dauphas said, including a refinement of the age of the Milky Way galaxy, which he published in 2005.
Hafnium and thorium both are refractory or non-volatile elements, meaning that their compositions remain relatively constant in meteorites. They also are lithophile elements, those that would have stayed in the mantle when the core of Mars formed. Thus, if scientists could measure the hafnium-thorium ratio in the martian mantle, they would have the ratio for the whole planet, which they need to reconstruct its formation history.
Mars-meteorite connection
The relationships between hafnium, thorium, and tungsten dictated that the hafnium-thorium ratio in the mantle of Mars must be similar to the same ratio in chondrites. To derive the martian mantle's hafnium-thorium ratio, they divided the thorium-tungsten ratio of the martian meteorites by the thorium-hafnium ratio of the chondrites.
"Why do you do that? Because thorium and tungsten have very similar chemical behavior," Dauphas said.
Once Dauphas and Pourmand had determined this ratio, they were able to calculate how long it took Mars to develop into a planet. A computer simulation based on these data showed that Mars must have reached half its present size only two million years after the formation of the solar system.
A quickly forming Mars would help explain the puzzling similarities in the xenon content of its atmosphere and that of Earth.
"Maybe it's just a coincidence, but maybe the solution is that part of the atmosphere of Earth was inherited from an earlier generation of embryos that had their own atmospheres, maybe a Marslike atmosphere," Dauphas said.
The short formation history of Mars further raises the possibility that aluminum 26, which is known from meteorites, turned the planet into a magma ocean early in it history. Aluminum 26 has a half-life of 700,000 years, so it would have disappeared too quickly to contribute to the internal heat of Earth.
If Mars formed in two million years, however, significant quantities of aluminum 26 would remain. "When this aluminum 26 decays it releases heat and can completely melt the planet," Pourmand said.
Funding source: National Aeronautics and Space Administration, the National Science Foundation, and the Packard Foundation.
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Not Again...

A fascinating, yet disturbing, article regarding geologic strain in the sea floor near Japan.


Japan Earthquake Appears to Increase Quake Risk Elsewhere in the Country

ScienceDaily (May 25, 2011) — Japan's recent magnitude 9.0 earthquake, which triggered a devastating tsunami, relieved stress along part of the quake fault but also has contributed to the build up of stress in other areas, putting some of the country at risk for up to years of sizeable aftershocks and perhaps new main shocks, scientists say.
After studying data from Japan's extensive seismic network, researchers from the Woods Hole Oceanographic Institution (WHOI), Kyoto University and the U.S. Geological Survey (USGS) have identified several areas at risk from the quake, Japan's largest ever, which already has triggered a large number of aftershocks.
Data from the magnitude 9.0 Tohoku earthquake on March 11 has brought scientists a small but perceptible step closer to a better assessment of future seismic risk in specific regions, said Shinji Toda of Kyoto University, a lead author of the study. "Even though we cannot forecast precisely, we can explain the mechanisms involved in such quakes to the public," he said. Still, he added, the findings do bring scientists "a little bit closer" to being able to forecast aftershocks.
"Research over the past two decades has shown that earthquakes interact in ways never before imagined," Toda, Jian Lin of WHOI and Ross S. Stein of USGS write in a summary of their paper in press for publication in the Tohoku Earthquake Special Issue of the journal Earth, Planets and Space. "A major shock does relieve stress -- and thus the likelihood of a second major tremor -- but only in some areas. The probability of a succeeding earthquake adjacent to the section of the fault that ruptured or on a nearby but different fault can jump" significantly.
The Tohoku earthquake, centered off northern Honshu Island, provided an "unprecedented" opportunity to utilize Japan's "superb monitoring networks" to gather data on the quake, the scientists said. The Tohoku quake, the fourth largest earthquake ever recorded, was "the best-recorded [large quake] the world has ever known."
This made the quake a "special" one in terms of scientific investigation, Lin said. "We felt we might be able to find something we didn't see before" in previous quakes, he said.
The magnitude 9 quake appears to have influenced large portions of Honshu Island, Toda said. At particular risk, he said, are the Tokyo area, Mount Fuji and central Honshu including Nagano.
The Kantu fragment, which is close to Tokyo, also experienced an increase in stress. Previous government estimates have put Tokyo at a 70 percent risk for a magnitude 7 earthquake over the next 30 years. The new data from the Tohoku quake increase those odds to "more than 70 percent," Toda said. "That is really high."
Using a model known as Coulomb stress triggering, Lin and his colleagues found measureable increases in stress along faults to the north at Sanriku-Hokobu, south at Off Boso and at the Outer Trench Slope normal faults east of the quake's epicenter off the Japan coast near the city of Sendai.
"Based on our other studies, these stress increases are large enough to increase the likelihood of triggering significant aftershocks or subsequent mainshocks," the researchers said.
Stein of the USGS emphasized the ongoing risk to parts of Japan. "There remains a lot of real estate in Japan--on shore and off--that could host large, late aftershocks of the Tohoku quake," he said.
"In addition to the megathrust surface to the north or south of the March 11 rupture, we calculate that several fault systems closer to Tokyo have been brought closer to failure, and some of these have lit up in small earthquakes since March 11. So, in our judgment, Central Japan, and Tokyo in particular, is headed for a long vigil that will not end anytime soon."
Lin added that aftershocks, as well as new mainshocks, could continue for "weeks, months, years."
Toda explained that the magnitude of future quakes is proportional to the length of the fault involved.
In a separate paper submitted to Geophysical Research Letters, the researchers "report on a broad and unprecedented increase in seismicity rate for microearthquakes over a broad (360 by 120 mile) area across inland Japan, parts of the Japan Sea and the Izu islands, following the 9.0 Tohoku mainshock."
"The crust on the land was turned on…far away from a fault," Lin said. Most of these are relatively small quakes -- magnitude 2 to 4 -- "but a lot of them," Lin said. "This is surprising; we've never seen this before," he said. "Such small events…may have happened following major quakes in other places but may have been missed due to poor seismic networks."
"The 9.0 Tohoku quake caught many people including scientists by surprise," Lin said. "It had been thought that a large quake in this area would go up to about 8.2, not 9.0" That estimate was significantly influenced by historical data. "The Tohoku quake reminded us that considering only the historical earthquakes is inadequate, even in a country of relatively long written records like Japan and China," he said.
"Historical records, and especially the instrumental records, are indeed too short to provide a full picture of the potential of large earthquakes in a region. Thus we must encourage many more studies to find geological evidence (for example, through analyzing sediment cores extracted on land and undersea) that might provide clues of large earthquake and tsunami events that occurred hundreds to thousands of years ago."
"We must recognize that because our knowledge is incomplete, our estimation of seismic hazard is likely to be underestimated in many cases. Thus we must prepare for potential hazard that might be worse than we already know," Lin said.
The finding that a quake such as this one can increase stresses elsewhere "means that new quakes could occur in the region," Lin said. "We must factor in this new information on stresses into earthquake preparedness.
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Monday, May 23, 2011

Joplin, MO Tornado

Guys,

This video of the Joplin tornado forming is amazing.  There is also some damage footage too.

It is amazing to see how quickly the tornado forms and then turns into a monster wedge tornado.  Shocking.  Please pray for the people of Joplin.
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Wednesday, May 18, 2011

Earth's Inner Core

Here is an interesting article on the earth's inner core.  It is most likely the source of the earth's magnetic field as well.


Earth's Core Is Melting ... and Freezing

ScienceDaily (May 18, 2011) — The inner core of Earth is simultaneously melting and freezing due to circulation of heat in the overlying rocky mantle, according to new research from the University of Leeds, UC San Diego and the Indian Institute of Technology.
The findings, published May 19Nature, could help us understand how the inner core formed and how the outer core acts as a 'geodynamo', which generates the planet's magnetic field.
"The origins of Earth's magnetic field remain a mystery to scientists," said study co-author Dr Jon Mound from the University of Leeds. "We can't go and collect samples from the centre of Earth, so we have to rely on surface measurements and computer models to tell us what's happening in the core."
"Our new model provides a fairly simple explanation to some of the measurements that have puzzled scientists for years. It suggests that the whole dynamics of Earth's core are in some way linked to plate tectonics, which isn't at all obvious from surface observations.
"If our model is verified it's a big step towards understanding how the inner core formed, which in turn helps us understand how the core generates the Earth's magnetic field."
Earth's inner core is a ball of solid iron about the size of our moon. This ball is surrounded by a highly dynamic outer core of a liquid iron-nickel alloy (and some other, lighter elements), a highly viscous mantle and a solid crust that forms the surface where we live.
Over billions of years, Earth has cooled from the inside out causing the molten iron core to partly freeze and solidify. The inner core has subsequently been growing at the rate of around 1mm a year as iron crystals freeze and form a solid mass.
The heat given off as the core cools flows from the core to the mantle to Earth's crust through a process known as convection. Like a pan of water boiling on a stove, convection currents move warm mantle to the surface and send cool mantle back to the core. This escaping heat powers the geodynamo and coupled with the spinning of Earth generates the magnetic field.
Scientists have recently begun to realise that the inner core may be melting as well as freezing, but there has been much debate about how this is possible when overall the deep Earth is cooling. Now the research team believes they have solved the mystery.
Using a computer model of convection in the outer core, together with seismology data, they show that heat flow at the core-mantle boundary varies depending on the structure of the overlying mantle. In some regions, this variation is large enough to force heat from the mantle back into the core, causing localised melting.
The model shows that beneath the seismically active regions around the Pacific 'Ring of Fire', where tectonic plates are undergoing subduction, the cold remnants of oceanic plates at the bottom of the mantle draw a lot of heat from the core. This extra mantle cooling generates down-streams of cold material that cross the outer core and freeze onto the inner core.
Conversely, in two large regions under Africa and the Pacific where the lowermost mantle is hotter than average, less heat flows out from the core. The outer core below these regions can become warm enough that it will start melting back the solid inner core.
Co-author Dr Binod Sreenivasan from the Indian Institute of Technology said: "If Earth's inner core is melting in places, it can make the dynamics near the inner core-outer core boundary more complex than previously thought.
"On the one hand, we have blobs of light material being constantly released from the boundary where pure iron crystallizes. On the other hand, melting would produce a layer of dense liquid above the boundary. Therefore, the blobs of light elements will rise through this layer before they stir the overlying outer core.
"Interestingly, not all dynamo models produce heat going into the inner core. So the possibility of inner core melting can also place a powerful constraint on the regime in which the Earth's dynamo operates."
Co-author Dr Sebastian Rost from the University of Leeds added: "The standard view has been that the inner core is freezing all over and growing out progressively, but it appears that there are regions where the core is actually melting. The net flow of heat from core to mantle ensures that there's still overall freezing of outer core material and it's still growing over time, but by no means is this a uniform process.
"Our model allows us to explain some seismic measurements which have shown that there is a dense layer of liquid surrounding the inner core. The localised melting theory could also explain other seismic observations, for example why seismic waves from earthquakes travel faster through some parts of the core than others."
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