The Moon may play a major role in maintaining Earth's magnetic field

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The gravitational effects associated with the presence of the Moon and Sun cause cyclical deformation of the Earth's mantle and wobbles in its rotation axis. This mechanical forcing applied to the whole planet causes strong currents in the outer core, which is made up of a liquid iron alloy of very low viscosity. Such currents are enough to generate the Earth's magnetic field.

Credit: © Julien Monteux and Denis Andrault

The Earth's magnetic field permanently protects us from the charged particles and radiation that originate in the Sun. This shield is produced by the geodynamo, the rapid motion of huge quantities of liquid iron alloy in the Earth's outer core. To maintain this magnetic field until the present day, the classical model required the Earth's core to have cooled by around 3,000 °C over the past 4.3 billion years. Now, a team of researchers from CNRS and Université Blaise Pascal[1] suggests that, on the contrary, its temperature has fallen by only 300 °C. The action of the Moon, overlooked until now, is thought to have compensated for this difference and kept the geodynamo active. Their work is published on 30 march 2016 in the journal Earth and Planetary Science Letters.

The classical model of the formation of Earth's magnetic field raised a major paradox. For the geodynamo to work, the Earth would have had to be totally molten four billion years ago, and its core would have had to slowly cool from around 6800 °C at that time to 3800 °C today. However, recent modeling of the early evolution of the internal temperature of the planet, together with geochemical studies of the composition of the oldest carbonatites and basalts, do not support such cooling. With such high temperatures being ruled out, the researchers propose another source of energy in their study.

The Earth has a slightly flattened shape and rotates about an inclined axis that wobbles around the poles. Its mantle deforms elastically due to tidal effects caused by the Moon. The researchers show that this effect could continuously stimulate the motion of the liquid iron alloy making up the outer core, and in return generate Earth's magnetic field. The Earth continuously receives 3,700 billion watts of power through the transfer of the gravitational and rotational energy of the Earth-Moon-Sun system, and over 1,000 billion watts is thought to be available to bring about this type of motion in the outer core. This energy is enough to generate the Earth's magnetic field, which together with the Moon, resolves the major paradox in the classical theory. The effect of gravitational forces on a planet's magnetic field has already been well documented for two of Jupiter's moons, Io and Europa, and for a number of exoplanets.

Since neither the Earth's rotation around its axis, nor the direction of its axis, nor the Moon's orbit are perfectly regular, their combined effect on motion in the core is unstable and can cause fluctuations in the geodynamo. This process could account for certain heat pulses in the outer core and at its boundary with the Earth's mantle.

Over the course of time, this may have led to peaks in deep mantle melting and possibly to major volcanic events at the Earth's surface. This new model shows that the Moon's effect on the Earth goes well beyond merely causing tides.

[1] At the Laboratoire Magmas et Volcans (CNRS/IRD/Université Blaise Pascal), part of the Observatoire de Physique du Globe de Clermont-Ferrand, the Institut de Recherche sur les Phénomènes Hors-équilibre (CNRS/Aix-Marseille Université/Ecole Centrale Marseille) and the Institut de Recherche en Astrophysique et Planétologie (CNRS/Université Toulouse III -- Paul Sabatier).

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The above post is reprinted from materials provided by CNRS. Note: Content may be edited for style and length.

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Journal Reference:

1. Denis Andrault, Julien Monteux, Michael Le Bars, Henri Samuel. The deep Earth may not be cooling down. Earth and Planetary Science Letters, 2016; DOI: 10.1016/j.epsl.2016.03.020

Getting to know more about sun storms

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A violent solar eruption can disrupt Earth's magnetic field, which in turn can interfere with power grids. In Washington, the White House is making contingency plans -- as is the electrical power sector in Norway.

One particular feature of sun storms which makes it important to be prepared is that they impact on large geographical areas at one and the same time. In 1989, a major sun stormdisabled the power system in Quebec in Canada, and in 2003 power cuts caused by a sun storm resulted in major economic consequences across the north-western USA. In our society in particular, which is so dependent on technology and infrastructure, sun storms have the potential to make a major negative impact.

SINTEF and NTNU are now planning to look into the effects of sun storms on electricity distribution in Norway for Statnett, Statkraft and the Norwegian Water Resources and Energy Directorate (NVE).

"Sun storms can cause stability problems resulting in power outages," says energy research scientist and Project Manager Atle Pedersen at SINTEF. "If the worst comes to the worst, they can also cause permanent damage to equipment such as transformers, which in turn may lead to prolonged power cuts," he says.

Studies since the 1990s "I suppose we're really waiting for something 'big' to happen," says Statnett's Trond Magne Ohnstad, who has been studying sun storms since the late 1990s. "Even then I wanted to find out whether sun storms represented a real threat to power supplies," he says.

In the beginning, Ohnstad studied internationally-authored articles and reports, and in 1999 Statnett installed measuring equipment on a transformer and recorded the geomagnetically-induced current (GIC) that arises following sun storms. Since 2003, measurements have been carried out at many other locations.

"I want to bring together a larger group of experts to study this topic here in Norway," says Ohnstad. "This is why we've launched a preliminary study to look into sun storms," he says.

The reason for this is that Statnett is currently making historic increases in investment in the power grid. At present, the Norwegian domestic power system is not particularly vulnerable to sun storms but, according to Statnett, it is vital to maintain skills and expertise levels in this field in order to ensure that supplies continue to remain stable.

Preparing for extreme space weather In October 2015 the White House presented a strategy designed to prepare itself against extreme sun storms (article in Norwegian).

Here in Norway, the NVE is doing the same.

"In recent years there has been an increasing focus on potential problems and damage associated with sun storms," says Senior Engineer Helge Ulsberg at the NVE. "And the NVE has been playing an active part," he says.

In its regulations governing preventive security and emergency preparedness linked to energy supplies, published in 2013, the NVE highlights two types of incident caused by sun storms requiring contingency measures. The first involves avoiding the disruption of GPS signals, and the second the protection of transformers from damage.

As well prepared as possible Energy researchers at SINTEF and NTNU have extensive experience in solving similar problems linked to the power system. And now they're going to assess the risks associated with sun storms, and come up with the most essential and cost-effective preventive measures.

"What is the best way to prepare when a sun storm is forecast?" asks Atle Pedersen. "We will use the project to find out," he concludes.

How sun storms can disrupt the power distribution grid?

Olve Moe, research scientist at SINTEF Energy Research explains:

A sun storm is capable of sending a jet stream of electrically-charged particles towards the Earth at very high velocities.

In practice, a single jet of charged particles represents a variable electrical current. Such a current will induce currents in conducting materials in its vicinity, in a similar way to an induction furnace. We observe the same effect when a powerful jet stream of charged particles originating from a sun storm sweeps across the Earth. The jet stream induces currents in metal constructions and other conductors.

This means that power lines are particularly vulnerable, partly because of their widespread extent and partly because they are electrically insulated from earth.

During any given sun storm, the size of the current of charged particles from the sun will vary. Several minutes may pass between each peak current event. The currents induced in the power lines by this phenomenon will vary at the same frequency as the variation in the current of charged particles.

For this reason, the current induced in the power lines by the sun storm will exhibit much slower variation (lower frequency) than the normal frequency transmitted by the grid (in Norway the grid carries 50Hz with a repeated peak value 50 times per second).

Because of this we often say that sun storms induce direct currents in the power lines, even though it is in fact a slowly varying and irregular alternating current.

The direct current is the core of the problem. Transformers, which are key components of the power distribution grid, are very sensitive to direct and slowly varying currents, and can be damaged in such situations. Direct currents can also cause indirect problems for transformers such as functional instability and the inadvertent disconnection of fuses leading to power cuts across large geographical areas.

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Bubble Nebula looks like a gigantic cosmic soap bubble

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The Bubble Nebula, also known as NGC 7653, is an emission nebula located 11,000 light-years away. This stunning new image was observed by the NASA/ESA Hubble Space Telescope to celebrate its 26th year in space.
Credit: NASA, ESA, Hubble Heritage Team
This new NASA/ESA Hubble Space Telescope image, released to celebrate Hubble's 26th year in orbit, captures in stunning clarity what looks like a gigantic cosmic soap bubble. The object, known as the Bubble Nebula, is in fact a cloud of gas and dust illuminated by the brilliant star within it. The vivid new portrait of this dramatic scene wins the Bubble Nebula a place in the exclusive Hubble hall of fame, following an impressive lineage of Hubble anniversary images.

Twenty six years ago, on 24 April 1990, the NASA/ESA Hubble Space Telescope was launched into orbit aboard the space shuttle Discovery as the first space telescope of its kind. Every year, to commemorate this momentous day in space history, Hubble spends a modest portion of its observing time capturing a spectacular view of a specially chosen astronomical object.

This year's anniversary object is the Bubble Nebula, also known as NGC 7635, which lies 8,000 light-years away in the constellation Cassiopeia. This object was first discovered by William Herschel in 1787 and this is not the first time it has caught Hubble's eye. However, due to its very large size on the sky, previous Hubble images have only shown small sections of the nebula, providing a much less spectacular overall effect. Now, a mosaic of four images from Hubble's Wide Field Camera 3 (WFC3) allows us to see the whole object in one picture for the first time.

This complete view of the Bubble Nebula allows us to fully appreciate the almost perfectly symmetrical shell which gives the nebula its name. This shell is the result of a powerful flow of gas -- known as a stellar wind -- from the bright star visible just to the left of centre in this image. The star, SAO 20575, is between ten and twenty times the mass of the Sun and the pressure created by its stellar wind forces the surrounding interstellar material outwards into this bubble-like form.

The giant molecular cloud that surrounds the star -- glowing in the star's intense ultraviolet radiation -- tries to stop the expansion of the bubble. However, although the sphere already measures around ten light-years in diameter, it is still growing, owing to the constant pressure of the stellar wind -- currently at more than 100,000 kilometres per hour!

Aside from the symmetry of the bubble itself, one of the more striking features is that the star is not located at the centre. Astronomers are still discussing why this is the case and how the perfectly round bubble is created nonetheless.

The star causing the spectacular colourful bubble is also notable for something less obvious. It is surrounded by a complex system of cometary knots, which can be seen most clearly in this image just to the right of the star. The individual knots, which are generally larger in size than the Solar System and have masses comparable to Earth's, consist of crescent shaped globules of dust with large trailing tails illuminated and ionised by the star. Observations of these knots, and of the nebula as a whole, help astronomers to better understand the geometry and dynamics of these very complicated systems.

As always, and twenty six years on, Hubble gives us much more than a pretty picture.

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The above post is reprinted from materials provided by ESA/Hubble Information Centre. Note: Content may be edited for style and length.

Seeing double: NASA missions measure solar flare from 2 spots in space

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During a December 2013 solar flare, three NASA missions observed a current sheet form -- a strong clue for explaining what initiates the flares. This animation shows four views of the flare from NASA's Solar Dynamics Observatory, NASA's Solar and Terrestrial Relations Observatory, and JAXA/NASA's Hinode, allowing scientists to make unprecedented measurements of its characteristics. The current sheet is a long, thin structure, especially visible in the views on the left. Those two animations depict light emitted by material with higher temperatures, so they better show the extremely hot current sheet.

Credit: NASA/JAXA/SDO/STEREO/Hinode (courtesy Zhu, et al.)

Solar flares are intense bursts of light from the sun. They are created when complicated magnetic fields suddenly and explosively rearrange themselves, converting magnetic energy into light through a process called magnetic reconnection -- at least, that's the theory, because the signatures of this process are hard to detect. But during a December 2013 solar flare, three solar observatories captured the most comprehensive observations of an electromagnetic phenomenon called a current sheet, strengthening the evidence that this understanding of solar flares is correct.

These eruptions on the sun eject radiation in all directions. The strongest solar flares can impact the ionized part of Earth's atmosphere -- the ionosphere -- and interfere with our communications systems, like radio and GPS, and also disrupt onboard satellite electronics. Additionally, high-energy particles -- including electrons, protons and heavier ions -- are accelerated by solar flares.

Unlike other space weather events, solar flares travel at the speed of light, meaning we get no warning that they're coming. So scientists want to pin down the processes that create solar flares -- and even some day predict them before our communications can be interrupted.

"The existence of a current sheet is crucial in all our models of solar flares," said James McAteer, an astrophysicist at New Mexico State University in Las Cruces and an author of a study on the December 2013 event, published on April 19, 2016, in the Astrophysical Journal Letters. "So these observations make us much more comfortable that our models are good."

And better models lead to better forecasting, said Michael Kirk, a space scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in the study. "These complementary observations allowed unprecedented measurements of magnetic reconnection in three dimensions," Kirk said. "This will help refine how we model and predict the evolution of solar flares."

Looking at Current Sheets

A current sheet is a very fast, very flat flow of electrically-charged material, defined in part by its extreme thinness compared to its length and width. Current sheets form when two oppositely-aligned magnetic fields come in close contact, creating very high magnetic pressure. Electric current flowing through this high-pressure area is squeezed, compressing it down to a very fast and thin sheet. It's a bit like putting your thumb over the opening of a water hose -- the water, or, in this case, the electrical current, is forced out of a tiny opening much, much faster. This configuration of magnetic fields is unstable, meaning that the same conditions that create current sheets are also ripe for magnetic reconnection.

"Magnetic reconnection happens at the interface of oppositely-aligned magnetic fields," said Chunming Zhu, a space scientist at New Mexico State University and lead author on the study. "The magnetic fields break and reconnect, leading to a transformation of the magnetic energy into heat and light, producing a solar flare."

Because current sheets are so closely associated with magnetic reconnection, observing a current sheet in such detail backs up the idea that magnetic reconnection is the force behind solar flares.

"You have to be watching at the right time, at the right angle, with the right instruments to see a current sheet," said McAteer. "It's hard to get all those ducks in a row."

This isn't the first time scientists have observed a current sheet during a solar flare, but this study is unique in that several measurements of the current sheet -- such as speed, temperature, density and size -- were observed from more than one angle or derived from more than method.

This multi-faceted view of the December 2013 flare was made possible by the wealth of instruments aboard three solar-watching missions: NASA's Solar Dynamics Observatory, or SDO, NASA's Solar and Terrestrial Relations Observatory, or STEREO -- which has a unique viewing angle on the far side of the sun -- and Hinode, which is a collaboration between the space agencies of Japan, the United States, the United Kingdom and Europe led by the Japan Aerospace Exploration Agency.

Even when scientists think they've spotted something that might be a current sheet in solar data, they can't be certain without ticking off a long list of attributes. Since this current sheet was so well-observed, the team was able to confirm that its temperature, density, and size over the course of the event were consistent with a current sheet.

As scientists work up a better picture of how current sheets and magnetic reconnection lead to solar eruptions, they'll be able to produce better models of the complex physics happening there -- providing us with ever more insight on how our closest star affects space all around us.

This research was funded by a CAREER grant from the National Science Foundation awarded to James McAteer.

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The above post is reprinted from materials provided by NASA/Goddard Space Flight Center. Note: Content may be edited for style and length.

Dark matter does not contain certain axion-like particles

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Illustration of how light is transformed into ALP by the galaxy.

Credit: Credits to Aurore Simonnet, Sonoma State University (for the active galaxy core) and to NASA/NOAA/GSFC/Suomi NPP/VIIRS/Norman Kuring (for image of earth).

Researchers at Stockholm University are getting closer to corner light dark-matter particle models. Observations can rule out some axion-like particles in the quest for the content of dark matter. The article is now published in the Physical Review Letters.

Physicists are still struggling with the conundrum of identifying more than 80 percent of the matter in the Universe. One possibility is that it is made up by extremely light particles which weigh less than a billionth of the mass of the electron. These particles are often called axion-like particles (ALPs). Since ALPs are hard to find, the researchers have not yet been able to test different types of ALPs that could be a part of the dark matter.

For the first time the researchers used data from NASA's gamma-ray telescope on the Fermi satellite to study light from the central galaxy of the Perseus galaxy cluster in the hunt for ALPs. The researchers found no traces of ALPs and, for the first time, the observations were sensitive enough to exclude certain types of ALPs (ALPs can only constitute dark matter if they have certain characteristics).

One cannot detect ALPs directly but there is a small chance that they transform into ordinary light and vice versa when travelling through a magnetic field. A research team at Stockholm University used a very bright light source, the central galaxy of the Perseus galaxy cluster, to look for these transformations. The energetic light, so-called gamma radiation, from this galaxy could change its nature to ALPs while traveling through the magnetic field that fills the gas between the galaxies in the cluster.

"The ALPs we have been able to exclude could explain a certain amount of dark matter. What is particularly interesting is that with our analysis we are reaching a sensitivity that we thought could only be obtained with dedicated future experiments on Earth," says Manuel Meyer, post-doc at the Department of Physics, Stockholm University.

Searches for ALPs with the Fermi telescope will continue. More than 80 percent of the matter in the Universe remains to identify. The mysterious dark matter shows itself only through its gravity, it does neither absorb nor radiate any form of light.

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The above post is reprinted from materials provided by Stockholm University. Note: Content may be edited for style and length.

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Journal Reference:

1. M. Ajello, A. Albert, B. Anderson, L. Baldini, G. Barbiellini, D. Bastieri, R. Bellazzini, E. Bissaldi, R. D. Blandford, E. D. Bloom, R. Bonino, E. Bottacini, J. Bregeon, P. Bruel, R. Buehler, G. A. Caliandro, R. A. Cameron, M. Caragiulo, P. A. Caraveo, C. Cecchi, A. Chekhtman, S. Ciprini, J. Cohen-Tanugi, J. Conrad, F. Costanza, F. D’Ammando, A. de Angelis, F. de Palma, R. Desiante, M. Di Mauro, L. Di Venere, A. Domínguez, P. S. Drell, C. Favuzzi, W. B. Focke, A. Franckowiak, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, D. Gasparrini, N. Giglietto, T. Glanzman, G. Godfrey, S. Guiriec, D. Horan, G. Jóhannesson, M. Katsuragawa, S. Kensei, M. Kuss, S. Larsson, L. Latronico, J. Li, L. Li, F. Longo, F. Loparco, P. Lubrano, G. M. Madejski, S. Maldera, A. Manfreda, M. Mayer, M. N. Mazziotta, M. Meyer, P. F. Michelson, N. Mirabal, T. Mizuno, M. E. Monzani, A. Morselli, I. V. Moskalenko, S. Murgia, M. Negro, E. Nuss, C. Okada, E. Orlando, J. F. Ormes, D. Paneque, J. S. Perkins, M. Pesce-Rollins, F. Piron, G. Pivato, T. A. Porter, S. Rainò, R. Rando, M. Razzano, A. Reimer, M. Sánchez-Conde, C. Sgrò, D. Simone, E. J. Siskind, F. Spada, G. Spandre, P. Spinelli, H. Takahashi, J. B. Thayer, D. F. Torres, G. Tosti, E. Troja, Y. Uchiyama, K. S. Wood, M. Wood, G. Zaharijas, S. Zimmer. Search for Spectral Irregularities due to Photon–Axionlike-Particle Oscillations with the Fermi Large Area Telescope. Physical Review Letters, 2016; 116 (16) DOI:10.1103/PhysRevLett.116.161101

Light echoes give clues to planet nursery around star

For the first time, astronomers used echoes of light to determine the distance from a star to the inner wall of its surrounding planet-forming disk of dust and gas

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This illustration shows a star surrounded by a protoplanetary disk. Material from the thick disk flows along the star's magnetic field lines and is deposited onto the star's surface. When material hits the star, it lights up brightly. The star's irregular illumination allows astronomers to measure the gap between the disk and the star by using a technique called "photo-reverberation" or "light echoes." First, astronomers look at how much time it takes for light from the star to arrive at Earth. Then, they compare that with the time it takes for light from the star to bounce off the inner edge of the disk and then arrive at Earth. That time difference is used to measure distance, as the speed of light is constant.

Credit: NASA/JPL-Caltech

Imagine you want to measure the size of a room, but it's completely dark. If you shout, you can tell if the space you're in is relatively big or small, depending on how long it takes to hear the echo after it bounces off the wall.

Astronomers use this principle to study objects so distant that they can't be seen as more than points. In particular, researchers are interested in calculating how far young stars are from the inner edge of their surrounding protoplanetary disks. These disks of gas and dust are sites where planets form over the course of millions of years.

"Understanding protoplanetary disks can help us understand some of the mysteries about exoplanets, the planets in solar systems outside our own," said Huan Meng, postdoctoral research associate at the University of Arizona's Department of Astronomy and Steward Observatory. "We want to know how planets form and why we find large planets called 'hot Jupiters' close to their stars."

Meng is the first author on a new study published in the Astrophysical Journalusing data from NASA's Spitzer Space Telescope and four ground-based telescopes to determine the distance from a star to the inner rim of its surrounding protoplanetary disk.

Making the measurement wasn't as simple as laying a ruler on top of a photograph. Doing so would be as impossible as using a satellite photo of your computer screen to measure the width of the period at the end of this sentence.

Instead, researchers used a method called "photo-reverberation," also known as "light echoes." When the central star brightens, some of the light hits the surrounding disk, causing a delayed "echo." Scientists measured the time it took for light coming directly from the star to reach Earth, then waited for its echo to arrive.

Thanks to Albert Einstein's theory of special relativity, we know that light travels at a constant speed. To determine a given distance, astronomers can multiply the speed of light by the time light takes to get from one point to another.

To take advantage of this formula, scientists needed to find a star with variable emission -- that is, a star that emits radiation in an unpredictable, uneven manner. Our own sun has a fairly stable emission, but a variable star would have unique, detectable changes in radiation that could be used for picking up corresponding light echoes. Young stars, which have variable emission, are the best candidates.

The star used in this study is called YLW 16B, which lies about 400 light-years from Earth. YLW 16B has about the same mass as our sun, but at one million years old, it's just a baby compared to our 4.6-billion-year-old home star.

Astronomers combined Spitzer data with observations from ground-based telescopes: the Mayall telescope at Kitt Peak National Observatory in Arizona, the SOAR and SMARTS telescopes in Chile, and the Harold L. Johnson telescope in Mexico. During two nights of observation, researchers saw consistent time lags between the stellar emissions and their echoes in the surrounding disk. The ground-based observatories detected the shorter-wavelength infrared light emitted directly from the star, and Spitzer observed the longer-wavelength infrared light from the disk's echo. Because of thick interstellar clouds that block the view from Earth, astronomers could not use visible light to monitor the star.

Researchers then calculated how far this light must have traveled during that time lag: about 0.08 astronomical units, which is approximately 8 percent of the distance between Earth and its sun, or one-quarter the diameter of Mercury's orbit. This was slightly smaller than previous estimates with indirect techniques, but consistent with theoretical expectations.

Although this method did not directly measure the height of the disk, researchers were able to determine that the inner edge is relatively thick.

Previously, astronomers have used the light echo technique to measure the size of accretion disks of material around supermassive black holes. Since no light escapes from a black hole, researchers compare light from the inner edge of the accretion disk to light from the outer edge to determine the disk size. This technique is also used to measure the distance to other features near the accretion disk, such as dust and the surrounding fast-moving gas.

While light echoes from supermassive black holes represent delays of days to weeks, scientists measured the light echo from the protoplanetary disk in this study to be a mere 74 seconds.

The Spitzer study marks the first time the light echo method was used in the context of protoplanetary disks. The approach can be applied to other systems of stars with planet-forming disks around them, the scientists pointed out.

"Knowing the exact position of the inner boundary of a protoplanetary disk is important to anyone who wants to understand planet evolution," Meng says.

Most stars are born with a protoplanetary disk around them, and astronomers have known for a long time that there is a gap between the star and its disk because of two competing processes: Close to the star, its strong radiation ionizes gas particles in the disk, diverting them along the star's magnetic field lines above and below the plane of the disk. The other mechanism that prevents the disk from reaching all the way to the star's surface is heat. Once a dust particle gets too close to the star, it simply vaporizes and either falls onto the star or gets blown out of the system.

"The predominant one of those two mechanisms plays an important role in the evolution of the disk, and right now, we don't know which it is," Meng says.

Until now, astronomers used a technique called interferometry to determine the position of the inner edge of protoplanetary disks, but that method requires assumptions about the shape of the disk, resulting in controversial findings.

"Our method provides a completely independent measurement of which mechanism plays the predominant role now and in the future," Meng says.

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Story Source:

The above post is reprinted from materials provided by University of Arizona. Note: Content may be edited for style and length.

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Journal Reference:

1. Huan Y. A. Meng, Peter Plavchan, George H. Rieke, Ann Marie Cody, Tina Güth, John Stauffer, Kevin Covey, Sean Carey, David Ciardi, Maria C. Duran-Rojas, Robert A. Gutermuth, María Morales-Calderón, Luisa M. Rebull, Alan M. Watson. Photo-reverberation Mapping of a Protoplanetary Accretion Disk around a T Tauri Star. Astrophysical Journal, 2016 [link]

From bright flare ribbons to coronal rain

High-resolution images capture a solar flare as it unfolds

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The impulsive phase of the solar flare, in which most energy is released.

Credit: NJIT

Scientists at NJIT's Big Bear Solar Observatory (BBSO) have captured unprecedented images of a recent solar flare, including bright flare ribbons seen crossing a sunspot followed by "coronal rain," plasma that condenses in the cooling phase shortly after the flare, showering the visible surface of the Sun where it lands in brilliant explosions.

The new images provide insights into one of the central puzzles of solar physics -- how energy is transferred from one region of the Sun to another during and after a solar flare, an explosive release of magnetic energy responsible for space weather.

"We can now observe in very fine detail how energy is transported in solar flares, in this case from the corona where it has been stored to the lower chromosphere tens of thousands of miles below it, where most of the energy is finally converted into heat and radiated away," said Ju Jing, a research professor in NJIT's Department of Physics and the lead author of the study, "Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6?m New Solar Telescope," published this week in Scientific Reports, a journal affiliated with the Nature group of publications.

Ju noted that while electron beams are traditionally seen as the major agent for transporting flare energy, the new observations provide novel information on the spatial scale of the energy transport.

Dale Gary, a distinguished professor of physics at NJIT and a co-author of the study, described the images as "the highest-resolution observations of this kind of activity we've had before."

"What is particularly interesting is that these bright areas of impact are so small in size that they have been present, but overlooked in previous observations with lower resolution," he added.

Captured by NJIT's 1.6 meter New Solar Telescope (NST) during a solar flare on June 22, 2015, the images of coronal rain are among a series of recent pictures captured by the NST providing scientists new insights into the complex dynamics of the Sun's multi-layered atmosphere and the massive eruptions on the star's surface.

NST's high-resolution observations have led to new information in particular on all phases of solar flares, including the instability of magnetic flux tubes that can trigger flares, the behavior of the bright flare ribbons that occur in the initial phase of flares, and new observations by Ju and her colleagues of the cooling phase.

"Ever since a solar flare was first detected by Carrington and Hodgson in 1859, this spectacular phenomenon of solar activity has been a subject of intense research and has served as a natural laboratory for understanding the physical processes of transient energy release throughout the universe," Ju noted in her recent paper.

The newly revealed solar phenomena will lead, the researchers hope, to a better understanding of their impact on Earth.

"Our measurements bridge the gap between models and observations, while also opening interesting avenues of future investigation," Ju said. "With large, ground-based telescopes, will we will be able to measure, for example, these features on the Sun's surface down to their fundamental spatial scale? We look forward to further investigation coupled with theoretical modeling to fully understand what we have observed."

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Story Source:

The above post is reprinted from materials provided by New Jersey Institute of Technology. The original item was written by Tracey Regan. Note: Content may be edited for style and length.

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Journal Reference:

1. Ju Jing, Yan Xu, Wenda Cao, Chang Liu, Dale Gary, Haimin Wang.Unprecedented Fine Structure of a Solar Flare Revealed by the 1.6 m New Solar Telescope. Scientific Reports, 2016; 6: 24319 DOI:10.1038/srep24319

Planet Nine: A world that shouldn't exist

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This is an artist's conception of Planet Nine.

Credit: Caltech/R. Hurt (IPAC)

Earlier this year scientists presented evidence for Planet Nine, a Neptune-mass planet in an elliptical orbit 10 times farther from our Sun than Pluto. Since then theorists have puzzled over how this planet could end up in such a distant orbit.

New research by astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) examines a number of scenarios and finds that most of them have low probabilities. Therefore, the presence of Planet Nine remains a bit of a mystery.

"The evidence points to Planet Nine existing, but we can't explain for certain how it was produced," says CfA astronomer Gongjie Li, lead author on a paper accepted for publication in the Astrophysical Journal Letters.

Planet Nine circles our Sun at a distance of about 40 billion to 140 billion miles, or 400 -- 1500 astronomical units. (An astronomical unit or A.U. is the average distance of the Earth from the Sun, or 93 million miles.) This places it far beyond all the other planets in our solar system. The question becomes: did it form there, or did it form elsewhere and land in its unusual orbit later?

Li and her co-author Fred Adams (University of Michigan) conducted millions of computer simulations in order to consider three possibilities. The first and most likely involves a passing star that tugs Planet Nine outward. Such an interaction would not only nudge the planet into a wider orbit but also make that orbit more elliptical. And since the Sun formed in a star cluster with several thousand neighbors, such stellar encounters were more common in the early history of our solar system.

However, an interloping star is more likely to pull Planet Nine away completely and eject it from the solar system. Li and Adams find only a 10 percent probability, at best, of Planet Nine landing in its current orbit. Moreover, the planet would have had to start at an improbably large distance to begin with.

CfA astronomer Scott Kenyon believes he may have the solution to that difficulty. In two papers submitted to the Astrophysical Journal, Kenyon and his co-author Benjamin Bromley (University of Utah) use computer simulations to construct plausible scenarios for the formation of Planet Nine in a wide orbit.

"The simplest solution is for the solar system to make an extra gas giant," says Kenyon.

They propose that Planet Nine formed much closer to the Sun and then interacted with the other gas giants, particularly Jupiter and Saturn. A series of gravitational kicks then could have boosted the planet into a larger and more elliptical orbit over time.

"Think of it like pushing a kid on a swing. If you give them a shove at the right time, over and over, they'll go higher and higher," explains Kenyon. "Then the challenge becomes not shoving the planet so much that you eject it from the solar system."

That could be avoided by interactions with the solar system's gaseous disk, he suggests.

Kenyon and Bromley also examine the possibility that Planet Nine actually formed at a great distance to begin with. They find that the right combination of initial disk mass and disk lifetime could potentially create Planet Nine in time for it to be nudged by Li's passing star.

"The nice thing about these scenarios is that they're observationally testable," Kenyon points out. "A scattered gas giant will look like a cold Neptune, while a planet that formed in place will resemble a giant Pluto with no gas."

Li's work also helps constrain the timing for Planet Nine's formation or migration. The Sun was born in a cluster where encounters with other stars were more frequent. Planet Nine's wide orbit would leave it vulnerable to ejection during such encounters. Therefore, Planet Nine is likely to be a latecomer that arrived in its current orbit after the Sun left its birth cluster.

Finally, Li and Adams looked at two wilder possibilities: that Planet Nine is an exoplanet that was captured from a passing star system, or a free-floating planet that was captured when it drifted close by our solar system. However, they conclude that the chances of either scenario are less than 2 percent.

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The above post is reprinted from materials provided by Harvard-Smithsonian Center for Astrophysics. Note: Content may be edited for style and length.

Sun’s magnetic field during the grand minimum is in fact at its maximum

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About 80 solar cycles seen from the surface, i.e. more than 1,000 years in solar time, modelled by means of a computer simulation. At 20-50 years in simulation time, a simulated grand minimum occurs, which in actual fact is the maximum of magnetic energy.

Credit: Image courtesy of Aalto University

The study of the Sun's long-term variation over a millennium by means of super computer modelling showed that during a time period of the Maunder Minimum type, the magnetic field may hide at the bottom of the convection zone.

The study conducted by the Aalto University Department of Computer Science, the ReSoLVE Centre of Excellence and the Max Planck Institute for Solar System Research seeks explanation for the mechanisms underlying the long-term variation in solar activity. The research team comprised Maarit Käpylä, Petri Käpylä, Nigul Olspert, Axel Brandenburg, Jaan Pelt, Jörn Warnecke and Bidya B. Karak. The recently published study was carried out by running a global computer model of the Sun on Finland's most powerful super computer over a period of six months.

'The Sun has an 11-year cycle that involves, among other things, the occurrence and disappearance of sunspots. The phenomena that occur in the Sun -- including the cycle -- change with time, so the solutions need to be integrated over time. Short-term variation is not interesting for the purposes of studying the space climate, for example,' says Maarit Käpylä, head of the DYNAMO team, who conducts astroinformatics or computational astrophysics and data-analysis at the Department of Computer Science.

As a result of the computation carried out, currently the world's longest numerical simulation was created that produces a solar-like dynamo solution complete with its long-term variation.

'The Sun as such is impossible to replicate on present-day computers -- or those of the near future -- due to its strong turbulence. And indeed we are not claiming that this modelling would really be the Sun. Instead, it is a 3D construction of various solar phenomena by means of which the star that runs our space climate can be better understood,' Käpylä explains.

What exactly is a grand minimum?

The largest surprise of the study relates to the Sun's silent periods known as grand minima, of which the Maunder Minimum is perhaps the best known. The solar magnetic field is thought to wither during it and be so weak as not being capable of generating sunspots or other activity.

'In fact, the magnetic field is at its maximum during the Maunder Minimum. Thus far, we have only been able to examine what is visible on the solar surface, but simulations enable us to see below the surface. During the Maunder Minimum, the magnetic field sinks to the bottom of the convection zone and is very strong there,' says Käpylä

The outer layer of the Sun, the convection zone, is like a boiling kettle with its moving and heat-transferring bubbles, and this not only generates a magnetic field, but also makes the entire area turbulent.

Maarit Käpylä will start as an independent group leader at one of Europe's leading solar research units, Max Planck Institute for Solar System Research, in the summer of 2016. The operations of the Aalto DYNAMO team at the ReSoLVE Centre of Excellence will continue under Käpylä's direction, focusing on even larger simulations using graphical processing units.

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The above post is reprinted from materials provided by Aalto University.Note: Content may be edited for style and length.

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Journal Reference:

1. M. J. Käpylä, P. J. Käpylä, N. Olspert, A. Brandenburg, J. Warnecke, B. B. Karak, J. Pelt. Multiple dynamo modes as a mechanism for long-term solar activity variations. Astronomy & Astrophysics, 2016; 589: A56 DOI: 10.1051/0004-6361/201527002

Satellites to see Mercury enter spotlight on May 9

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2016 Mercury transit path. Transits provide a great opportunity to study the way planets and stars move in space -- information that has been used throughout the ages to better understand the solar system and which still helps scientists today calibrate their instruments. Three of NASA's solar telescopes will watch the transit for just that reason.

Credit: Image courtesy of NASA/Goddard Space Flight Center

It happens only a little more than once a decade and the next chance to see it is Monday, May 9, 2016. Throughout the U.S., sky watchers can watch Mercury pass between Earth and the sun in a rare astronomical event known as a planetary transit. Mercury will appear as a tiny black dot as it glides in front of the sun s blazing disk over a period of seven and a half hours. Three NASA satellites will be providing images of the transit and one of them will have a near-live feed.

Although Mercury zooms around the sun every 88 days, Earth, the sun and Mercury rarely align. And because Mercury orbits in a plane that is tilted from Earths orbit, it usually moves above or below our line of sight to the sun. As a result, Mercury transits occur only about 13 times a century.

Transits provide a great opportunity to study the way planets and stars move in space -- information that has been used throughout the ages to better understand the solar system and which still helps scientists today calibrate their instruments. Three of NASA's solar telescopes will watch the transit for just that reason.

The May 9 Mercury transit will occur between about 7:12 a.m. and 2:42 p.m. EDT. Mercury is too small to see without magnification, but it can be seen with a telescope or binoculars. These must be outfitted with a solar filter as you can't safely look at the sun directly. Without the correct solar filter looking direction at the sun can cause serious irreversible eye damage.

Astronomers get excited when any two things come close to each other in the heavens said Louis Mayo, program manager at NASA s Goddard Space Flight Center in Greenbelt, Maryland. This is a big deal for us.

Mercury transits have been key to helping astronomers throughout history: In 1631, astronomers first observed a Mercury transit. Those observations allowed astronomers to measure the apparent size of Mercury s disk, as well as help them estimate the distance from Earth to the sun.

Back in 1631, astronomers were only doing visual observations on very small telescopes by today s standards said Mayo.

Since then, technological advancements have allowed us to study the sun and planetary transits in greater detail. In return, transits allow us to test our spacecraft and instruments.

Scientists for the Solar and Heliospheric Observatory, or SOHO (jointly operated by NASA and ESA, the European Space Agency), and NASA s Solar Dynamics Observatory, or SDO, will work in tandem to study the May 9 transit. The Hinode solar mission will also observe the event. Hinode is a collaboration between the space agencies of Japan, the United States, the United Kingdom and Europe led by the Japan Aerospace Exploration Agency.

SOHO launched in December 1995 with 12 instruments to study the sun from the deep solar core all the way out to the sun's effects on the rest of the solar system. Two of these instruments the Extreme ultraviolet Imaging Telescope and the Michelson Doppler Imager will be brought back into full operation to take measurements during the transit after five years of quiescence.

For one thing, the SOHO will measure the sun s rotation axis using images captured by the spacecraft.

Instruments on board SDO and SOHO use different spectral lines, different wavelengths and they have slightly different optical properties to study solar oscillations, said SOHO Project Scientist Joseph Gurman. "Transit measurements will help us better determine the solar rotation axis."

Such data is another piece of a long line of observations, which together help us understand how the sun changes over hours, days, years and decades.

It used to be hard to observe transits, Gurman said. If you were in a place that had bad weather, for example, you missed your chance and had to wait for the next one. These instruments help us make our observations, despite any earthly obstacles.

SDO will be able to use the transit to help with instrument alignment. Because scientists know so precisely where Mercury should be in relationship to the sun, they can use it as a marker to fine tune exactly how their instruments should be pointed.

The transit can also be used to help calibrate space instruments. The utter darkness of the planet provides an opportunity to study effects on the observations of stray light within the instrument. The backside of Mercury should appear black as it moves across the face of the sun. But because instruments scatter some light, Mercury will look slightly illuminated.

"It's like getting a cataract, you see stars or halos around bright lights as though you are looking through a misty windshield," said SDO Project Scientist Dean Pesnell.We have the same problem with our instruments.

Scientists run software on the images to try and mitigate the effect and check whether it can remove all of the scattered light.

For those of us down on the ground, it is worth trying to find a local astronomy club with a solar telescope to see if you can witness this rare event. Alternatively, a near-live feed of SDO images will be available athttp://www.nasa.gov/transit.

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The above post is reprinted from materials provided by NASA/Goddard Space Flight Center. Note: Content may be edited for style and length.