Iron 'snow' helps maintain Mercury's magnetic field

New scientific evidence suggests that deep inside the planet Mercury, iron "snow" forms and falls toward the center of the planet, much like snowflakes form in Earth's atmosphere and fall to the ground.

The movement of this iron snow could be responsible for Mercury's mysterious magnetic field, say researchers from the University of Illinois and Case Western Reserve University. In a paper published in the April issue of the journal Geophysical Research Letters, the scientists describe laboratory measurements and models that mimic conditions believed to exist within Mercury's core.

"Mercury's snowing core opens up new scenarios where convection may originate and generate global magnetic fields," said U. of I. geology professor Jie "Jackie" Li. "Our findings have direct implications for understanding the nature and evolution of Mercury's core, and those of other planets and moons."

Mercury is the innermost planet in our solar system and, other than Earth, the only terrestrial planet that possesses a global magnetic field. Discovered in the 1970s by NASA's Mariner 10 spacecraft, Mercury's magnetic field is about 100 times weaker than Earth's. Most models cannot account for such a weak magnetic field.

Made mostly of iron, Mercury's core is also thought to contain sulfur, which lowers the melting point of iron and plays an important role in producing the planet's magnetic field.

"Recent Earth-based radar measurements of Mercury's rotation revealed a slight rocking motion that implied the planet's core is at least partially molten," said Illinois graduate student Bin Chen, the paper's lead author. "But, in the absence of seismological data from the planet, we know very little about its core."

To better understand the physical state of Mercury's core, the researchers used a multi-anvil apparatus to study the melting behavior of an iron-sulfur mixture at high pressures and high temperatures.

In each experiment, an iron-sulfur sample was compressed to a specific pressure and heated to a specific temperature. The sample was then quenched, cut in two, and analyzed with a scanning electron microscope and an electron probe microanalyzer.

"Rapid quenching preserves the sample's texture, which reveals the separation of the solid and liquid phases, and the sulfur content in each phase," Chen said. "Based on our experimental results, we can infer what is going on in Mercury's core."

As the molten, iron-sulfur mixture in the outer core slowly cools, iron atoms condense into cubic "flakes" that fall toward the planet's center, Chen said. As the iron snow sinks and the lighter, sulfur-rich liquid rises, convection currents are created that power the dynamo and produce the planet's weak magnetic field.

Mercury's core is most likely precipitating iron snow in two distinct zones, the researchers report. This double-snow state may be unique among the terrestrial planets and terrestrial-like moons in our solar system.

"Our findings provide a new context into which forthcoming observational data from NASA's MESSENGER spacecraft can be placed," Li said. "We can now connect the physical state of our innermost planet with the formation and evolution of terrestrial planets in general."

With Li and Chen, Case Western Reserve University planetary geodynamics professor Steven A. Hauck II was a co-author of the paper.

The work was funded by the National Science Foundation.

http://www.astronomyreport.com/Research/Ir...entists_say.asp

XMM-Newton discovers part of missing matter in the universe


This is a model of the cosmic web. Clusters of galaxies are expected to
develop at the intersections of the web. Credits: Springel et al., Virgo Consortium

10 years ago, scientists predicted that about half of the missing ‘ordinary’ or normal matter made of atoms exists in the form of low-density gas, filling vast spaces between galaxies.

All the matter in the universe is distributed in a web-like structure. At dense nodes of the cosmic web are clusters of galaxies, the largest objects in the universe. Astronomers suspected that the low-density gas permeates the filaments of the web.

The low density of the gas hampered many attempts to detect it in the past. With XMM-Newton’s high sensitivity, astronomers have discovered its hottest parts. The discovery will help them understand the evolution of the cosmic web.

Only about 5% of our universe is made of normal matter as we know it, consisting of protons and neutrons, or baryons, which along with electrons, form the building blocks of ordinary matter. The rest of our universe is composed of elusive dark matter (23%) and dark energy (72%).

Small as the percentage might be, half of the ordinary baryonic matter is unaccounted for. All the stars, galaxies and gas observable in the universe account for less than a half of all the baryons that should be around.

Scientists predicted that the gas would have a high temperature and so it would primarily emit low-energy X-rays. But its very low density made observation difficult.

Astronomers using XMM-Newton were observing a pair of galaxy clusters, Abell 222 and Abell 223, situated at a distance of 2300 million light-years from Earth, when the images and spectra of the system revealed a bridge of hot gas connecting the clusters.

"The hot gas that we see in this bridge or filament is probably the hottest and densest part of the diffuse gas in the cosmic web, believed to constitute about half the baryonic matter in the universe," says Norbert Werner from SRON Netherlands Institute for Space Research, leader of the team reporting the discovery.

“The discovery of the warmest of the missing baryons is important. That’s because various models exist and they all predict that the missing baryons are some form of warm gas, but the models tend to disagree about the extremes,” adds Alexis Finoguenov, a team member.

Even with XMM-Newton’s sensitivity, the discovery was only possible because the filament is along the line of sight, concentrating the emission from the entire filament in a small region of the sky. The discovery of this hot gas will help better understand the evolution of the cosmic web.

"This is only the beginning. To understand the distribution of the matter within the cosmic web, we have to see more systems like this one. And ultimately launch a dedicated space observatory to observe the cosmic web with a much higher sensitivity than possible with current missions. Our result allows to set up reliable requirements for those new missions." concludes Norbert Werner.

ESA’s XMM-Newton Project Scientist, Norbert Schartel, comments on the discovery, “This important breakthrough is great news for the mission. The gas has been detected after hard work and more importantly, we now know where to look for it. I expect many follow-up studies with XMM-Newton in the future targeting such highly promising regions in the sky.”

http://www.esa.int/esaCP/SEMQLPZXUFF_index_0.html

Here is a very high resolution picture of the cosmic web: http://www.esa.int/images/Cosmic_web_H.jpg

Notice how similar it is to the human neuron. Another piece of data supporting the idea that everything is connected, an ancient truth.

Cosmic time warp revealed in slow-motion supernovae

Once upon a time, time was different. Supernova explosions in the early universe appear to age more slowly than today's supernovae, as if time itself was running slower back then, according to a recent series of astronomical observations. This cosmic time warp is exactly what should be produced by the expansion of the universe, confirming conventional big bang theory.

In that mainstream picture, the fabric of space is expanding everywhere – an idea predicted by Einstein's general theory of relativity and tested by observation.

Among other things, the expansion explains why light from distant galaxies is reddened when it reaches us. On its journey, over billions of years, the light has been stretched out to longer wavelengths – or "redshifted" – by the expansion of space.

The same effect means that an ancient event should appear to unfold more slowly than an otherwise identical event in the present day.

If we could see a giant clock in the early universe, sending out a flash of light once a second, those flashes of light would move farther apart on their way to us as the space between them expands, so there would be more than a second between successive flashes reaching Earth.

Astronomers have already found evidence of this "time dilation" in type Ia supernova, the catastrophic thermonuclear explosion of a white dwarf star.
Cosmic clock

Having seen and analysed many nearby type Ia supernovae, astronomers know that they age in a reliable way, making them the nearest thing to a cosmic clock. "Type Ia supernovae are just so predictable," says Peter Garnavich of Notre Dame University in Indiana, US, who worked on the latest study.

The best way to read one of these exploding stellar clocks is to look at the spectrum of light it emits, which changes over the course of a few weeks as the supernova expands.

"At first, only the outer layers of the supernova are visible. As time passes by, the outer layers thin out, and we are able to see deeper and deeper layers of the supernova ejecta," says lead author Stéphane Blondin of Harvard University in Cambridge, Massachusetts, US.

Those deeper layers tend to contain heavier chemical elements, which emit different characteristic wavelengths of light. "These changes in chemical composition as deeper layers become visible leave an imprint on the resulting spectrum," Blondin told New Scientist.

In two earlier studies, individual supernovae appeared to age slowly, showing evidence of time dilation.

In the new research, an international team of astronomers have gone much further by monitoring 13 supernovae at a range of redshifts, and therefore a range of distances. The earliest and most distant of these slow-mo explosions appeared to age at only about 60% of the normal rate seen in supernovae today.

The amount of time dilation increases with redshift, as expected if both are caused by the expansion of space.

Future observations will be able to test that correspondence more closely. "Any deviation from the predicted time-dilation factor would have profound implications for cosmology," says Blondin.

http://space.newscientist.com/article/dn13...supernovae.html

Glaciers reveal Martian climate has been recently active

The prevailing thinking is that Mars is a planet whose active climate has been confined to the distant past. About 3.5 billion years ago, the Red Planet had extensive flowing water and then fell quiet - deadly quiet. It didn't seem the climate had changed much since.

Now, in a research article that graces the May cover of Geology, scientists at Brown University think Mars's climate has been much more dynamic than previously believed. After examining stunning high-resolution images taken last year by the Mars Reconnaissance Orbiter, the researchers have documented for the first time that ice packs at least 1 kilometer (0.6 miles) thick and perhaps 2.5 kilometers (1.6 miles) thick existed along Mars's mid-latitude belt as recently as 100 million years ago. In addition, the team believes other images tell them that glaciers flowed in localized areas in the last 10 to 100 million years - akin to the day before yesterday in Mars's geological timeline.

This evidence of recent activity means the Martian climate may change again and could bolster speculation about whether the Red Planet can, or did, support life.

"We've gone from seeing Mars as a dead planet for three-plus billion years to one that has been alive in recent times," said Jay Dickson, a research analyst in the Department of Geological Sciences at Brown and lead author of the Geology paper. "[The finding] has changed our perspective from a planet that has been dry and dead to one that is icy and active."

In fact, Dickson and his co-authors, James Head, a planetary geologist and the Louis and Elizabeth Scherck Distinguished Professor at Brown, and David Marchant, an associate professor in the Department of Earth Sciences at Boston University, believe the images show that Mars has gone through multiple Ice Ages - episodes in its recent past in which the planet's mid-latitudes were covered by glaciers that disappeared with changes in the Red Planet's obliquity, which changes the climate by altering the amount of sunlight falling on different areas.

Dickson and the other researchers focused on an area called Protonilus Mensae-Coloe Fossae. The region is located in Mars's mid-latitude and is marked by splotches of mesas, massifs and steep-walled valleys that separate the lowlands in the north from the highlands in the south.

The team looked in particular at a box canyon set in a low-lying plain. Images show the canyon has moraines - deposits of rocks that mark the limits of a glacier's advance or the path of its retreat. The rock deposit lines appear to show a glacier that flowed up the box canyon, which "physically cannot happen," Dickson said.

Instead, the team deduced the ice in the surrounding plain grew higher than the canyon's walls and then flowed downward onto the top of the canyon, which had become the lowest point on the ice-laden terrain. The team calculated the ice pack must have been one kilometer thick by past measurements of height between the plain and the lip of the canyon. Based on the ice flow patterns, the ice pack could have reached 2.5 kilometers at peak thickness during a period known as the late Amazonian, the authors said.

The finding could have implications for the life-on-Mars argument by strengthening the case for liquid water. Ice can melt two ways: by temperature or by pressure. As currently understood, the Martian climate is dominated by sublimation, the process by which solid substances are transformed directly to vapor. But ice packs can exert such strong pressure
at the base to produce liquid water, which makes the thickness of past glaciers on its surface so intriguing.

Dickson also looked at a lobe across the valley from the box canyon site. There, he saw a clear, semi-circular moraine that had spilled from an ancient tributary on to the surrounding plain. The lobe is superimposed on a past ice deposit and appears to be evidence of more recent glaciation. Although geologists can't date either event, the landscape appears to show at least two periods in which glaciation occurred, bolstering their theory that the Martian climate has undergone past Ice Ages.

http://physorg.com/news128174644.html

Radio telescope reveals secrets of massive black hole

At the cores of many galaxies, supermassive black holes expel powerful jets of particles at nearly the speed of light. Just how they perform this feat has long been one of the mysteries of astrophysics.

The leading theory says the particles are accelerated by tightly-twisted magnetic fields close to the black hole, but confirming that idea required an elusive close-up view of the jet's inner throat. Now, using the unrivaled resolution of the National Radio Astronomy Observatory's Very Long Baseline Array (VLBA), astronomers have watched material winding a corkscrew outward path and behaving exactly as predicted by the theory. The astronomers reported their findings in the April 24 issue of the journal Nature.

"We have gotten the clearest look yet at the innermost portion of the jet, where the particles actually are accelerated, and everything we see supports the idea that twisted, coiled magnetic fields are propelling the material outward," said Alan Marscher, of Boston University, leader of an international research team. "This is a major advance in our understanding of a remarkable process that occurs throughout the Universe," he added.

Marscher's team studied a galaxy called BL Lacertae (BL Lac), some 950 million light-years from Earth. BL Lac is a blazar, the most energetic type of black-hole-powered galactic core. A black hole is a concentration of mass so dense that not even light can escape its gravitational pull. Supermassive black holes in galaxies' cores power jets of particles and intense radiation in similar objects including quasars and Seyfert galaxies.

Material pulled inward toward the black hole forms a flattened, rotating disk, called an accretion disk. As the material moves from the outer edge of the disk inward, magnetic field lines perpendicular to the disk are twisted, forming a tightly-coiled bundle that, astronomers believe, propels and confines the ejected particles. Closer to the black hole, space itself, including the magnetic fields, is twisted by the strong gravitational pull and rotation of the black hole.

Theorists predicted that material moving outward in this close-in acceleration region would follow a corkscrew-shaped path inside the bundle of twisted magnetic fields. They also predicted that light and other radiation emitted by the moving material would brighten when its rotating path was aimed most directly toward Earth.

Marscher and his colleagues predicted there would also be a flare later when the material hits a stationary shock wave called the "core" some time after it has emerged from the acceleration region.

"That behavior is exactly what we saw," Marscher said, when his team followed an outburst from BL Lac. In late 2005 and early 2006, the astronomers watched BL Lac with an international collection of telescopes as a knot of material was ejected outward through the jet. As the material sped out from the neighborhood of the black hole, the VLBA could pinpoint its location, while other telescopes measured the properties of the radiation emitted from the knot.

Bright bursts of light, X-rays, and gamma rays came when the knot was precisely at locations where the theories said such bursts would be seen. In addition, the alignment of the radio and light waves -- a property called polarization -- rotated as the knot wound its corkscrew path inside the tight throat of twisted magnetic fields.

"We got an unprecedented view of the inner portion of one of these jets and gained information that's very important to understanding how these tremendous particle accelerators work," Marscher said.

http://physorg.com/news128174330.html

Dark matter may have been found on Earth

Particles of invisible "dark matter" have been detected deep inside a mountain in Italy, a collaboration of Italian and Chinese physicists claims. But others remain sceptical of the result, because other experiments have failed to detect any dark matter at all.

On Wednesday 16 April, at a workshop in Venice, Italy, the Dark Matter (DAMA) collaboration announced the results of the 4-year second phase of its experiment. DAMA scientists claimed to see dark matter back in 2003, but some scientists believed the result was a quirk of statistics. Now the evidence is stronger.

"We are pretty sure now that this [signal] is not a statistical fluke. What it means is another matter," says Francis Halzen, an astroparticle physicist at the University of Wisconsin-Madison, US. He spoke to New Scientist after attending the announcement by DAMA project leader Rita Bernabei of the University of Rome, Italy.

Unidentified substance

Astronomers believe our galaxy is awash with particles of dark matter, the invisible, unidentified substance that makes up nearly 90% of the matter in the universe. So far, the existence of dark matter in space has only been determined by its gravitational pull on normal stars and galaxies.

The DAMA experiment has looked more directly for dark matter particles hitting the Earth. The experiment takes place in an underground laboratory that lies beneath 1.4 kilometres of rock, inside the Gran Sasso mountain in Italy. The team looks for flashes of light in a sodium iodide detector.

The flashes mainly come from background "noise", such as ordinary neutrons from radioactivity in the surrounding rock. But some might also come from dark matter particles, and, if so, the scientists expect to see seasonal variations in the signal because the Earth's speed through our galaxy changes depending on its direction of motion.

This theory predicts that the Earth should be hit by more dark matter particles in June, when it is moving through the galaxy in the same direction as the Sun. There would also be fewer particles in December, when it is moving in the opposite direction.
Intense scepticism

That’s exactly what the DAMA team reported in 2003, following the first phase of their experiment, which ran for 7 years with a 100-kilogram detector. But the results were met with intense scepticism, as none of the other experiments looking for dark matter had seen anything.

So the DAMA team renewed their search with a larger 250-kilogram detector. And they say they can now confirm that the new experiment has again shown an annual variation in the number of particles hitting their detector. There is a slight increase above the average in June rate and a corresponding decrease in December.

The team claims that the new result is highly significant. The odds that they are simply seeing a random fluctuation are less than one in several billion, they say. They also say they have ruled out the possibility that the signal is due to some systematic effect, such as seasonal variations in the temperature of their underground cavern.

But Halzen is wary. "The discussion about whether this is some unknown systematic effect remains," he says.

Richard Gaitskell from Brown University at Providence, Rhode Island, US, and a member of two dark matter experiments – the Cryogenic Dark Matter Search (CDMS) and the Xenon project – also remains sceptical, because no other experiment has seen signs of dark matter.

"Right now, it is very difficult to reconcile theoretically what they are seeing and what we are seeing," says Gaitskell.

But both Halzen and Gaitskell agree that the new DAMA results might prompt others to try and duplicate the results. "The issue of dark matter is important enough that we should pay attention to this; we should not just ignore it," says Halzen.

http://space.newscientist.com/article/dn13...d-on-earth.html

Milky Way's monster black hole awoke 300 years ago

A black hole slumbering at the centre of our galaxy went into a "feeding frenzy" three centuries ago, the European Space Agency (ESA) said on Tuesday.

Located around 26,000 light years from Earth, the black hole, known as Sagittarius A-star (Sgr A*), is a monster with a mass four million times that of the Sun.

Japanese astronomers, using ESA's XMM-Newton orbital telescope and US and Japanese X-ray satellites, discovered that clouds of gas brightened and faded in X-ray light when they passed near Sgr A*'s maw, ESA said in a press release.

The phenomenon is due to X-ray pulses that are believed to be residual bursts from a flare that happened 300 years ago.

"We have wondered why the Milky Way's black hole appears to be a slumbering giant," team leader Tatsuya Inui of Kyoto University said.

"But now we realise that the black hole was far more active in the past. Perhaps it's just resting after a major outburst."

One theory is that a few centuries ago, the powerful gravitational pull of the black hole engulfed clouds of gas from an exploding star called a supernova, ESA said.

The "temporary feeding frenzy" caused X-ray energy to leap from its mouth in a giant flare.

http://news.yahoo.com/s/afp/20080415/sc_af...oJnyqBPh77POrgF

Before the Big Bang: A Twin Universe?

Until very recently, asking what happened at or before the Big Bang was considered by physicists to be a religious question. General relativity theory just doesn’t go there – at T=0, it spews out zeros, infinities, and errors – and so the question didn’t make sense from a scientific view.

But in the past few years, a new theory called Loop Quantum Gravity (LQG) has emerged. The theory suggests the possibility of a “quantum bounce,” where our universe stems from the collapse of a previous universe. Yet what that previous universe looked like was still beyond answering.

Now, physicists Alejandro Corichi from Universidad Nacional Autónoma de México and Parampreet Singh from the Perimeter Institute for Theoretical Physics in Ontario have developed a simplified LQG model that gives an intriguing answer: a pre-Big Bang universe might have looked a lot like ours. Their study will appear in an upcoming issue of Physical Review Letters.

“The significance of this concept is that it answers what happened to the universe before the Big Bang,” Singh told PhysOrg.com. “It has remained a mystery, for models that could resolve the Big Bang singularity, whether it is a quantum foam or a classical space-time on the other side. For instance, if it were a quantum foam, we could not speak about a space-time, a notion of time, etc. Our study shows that the universe on the other side is very classical as ours.”

The finding builds on previous research, with some important differences. Last year, Penn State physicist Martin Bojowald used a simplified version of LQG to show that a universe “on the other side” of the bounce could have existed. However, although that model produced valid math, no observations of our current universe could have lead to any understanding of the state of the pre-bounce universe, as nothing was preserved across the bounce. Bojowald described this as a sort of “cosmic amnesia.”

But Corichi and Singh have modified the simplified LQG theory further by approximating a key equation called the quantum constraint. Using their version, called sLQG, the researchers show that the relative fluctuations of volume and momentum in the pre-bounce universe are conserved across the bounce.

“This means that the twin universe will have the same laws of physics and, in particular, the same notion of time as in ours,” Singh said. “The laws of physics will not change because the evolution is always unitary, which is the nicest way a quantum system can evolve. In our analogy, it will look identical to its twin when seen from afar; one could not distinguish them.”

That means that our universe today, roughly 13.7 billion years after the bounce, would share many of the same properties of the pre-bounce universe at 13.7 billion years before the bounce. In a sense, our universe has a mirror image of itself, with the Big Bang (or bounce) as the line of symmetry.

“In the universe before the bounce, all the general features will be the same,” said Singh. “It will follow the same dynamical equations, the Einstein’s equations when the universe is large. Our model predicts that this happens when the universe becomes of the order 100 times larger than the Planck size. Further, the matter content will be the same, and it will have the same evolution. Since the pre-bounce universe is contracting, it will look as if we were looking at ours backward in time.”

Specifically, Corichi and Singh calculate that the change in relative fluctuations across the bounce is less than 10-56, a number which becomes even smaller for universes that grow larger than 1 megaparsec (our universe is somewhere between 3,000 and 6,000 megaparsecs).

As the researchers explain, having an identical twin universe would not necessarily mean that every single feature of both universes would be identical. For instance, it doesn’t imply that there was another you that existed at some point, a person who has already lived your life.

“If one were able to look at certain microscopic properties with a very strong microscope – a very high-energy experiment probing the Planck scale – one might see differences in some quantities, just as one might see that twins have different fingerprints or one has a mole and the other does not, or a different DNA,” Singh said.

As Singh explained, there are still many questions regarding the details of the possible pre-bounce universe.

“The biggest question is whether these features survive when we consider more complex situations,” he said. “For example, one would like to know whether some structures present in the previous universe – like galaxies – will leave some imprint in the new expanding one that will give rise to identical structure or just 'similar.' For instance, it could happen that, in the previous universe, galaxies formed in a different way, so one might have a different distribution of galaxies on the other side. We will be able to answer this question when we understand these models.”

Ultimately, Corichi and Singh’s model might even tell us what a future universe would look like. Depending on how fast our present universe is accelerating – which will ultimately determine its fate – there’s a possibility that a generalization of the model would predict a re-collapse of our own universe.

“Such a universe will have many bounces from one branch to another,” Singh said. “It is also possible that universes in different branches will be identical.”

http://www.physorg.com/news126955971.html

Smallest extrasolar planet discovered

Spanish astronomers Wednesday announced the discovery of the smallest planet discovered to date outside the solar system, located 30 light years from earth.

The planet, "GJ 436T", was detected through a new technique which "will allow us to discover in less than 10 years the first planet resembling earth in terms of mass and orbit," said Ignasi Ribas of Spain's CSIC scientific research institute.

It was discovered by a team led by Ribas through its gravitational pull on other planets already discovered around the same star in the constellation of Leo.

"GJ 436T" has a mass five times the size of Earth, which makes it the smallest extrasolar planet among the roughly 300 identified so far, Ribas said in announcing the discovery.

He said the new planet is uninhabitable due to the distance that separates it from its star, which is far less than that between the earth and the sun.

To sustain life, a planet must have a mass similar to that of earth, liquid water on its surface, an atmosphere and a similar orbital distance from its star as that of the earth from the sun.

Initial calculations by the team indicated that "GJ 436T" rotates in 4.2 earth days and orbits its star every 5.2 days.

http://news.yahoo.com/s/afp/20080409/sc_af...Qu3QXrUwHjPOrgF