Aurora – astroengine.com

Earth’s Magnetic Field Just Hit a Phantom Speed Bump

Earth likely passed through “a fold in the heliospheric current sheet,” which induced a powerful electrical surge down here on the ground.

While science news is filled with rumbling earthquakes and rippling gravitational waves, a different kind of perturbation was felt in Norway yesterday (Jan. 6)—but its cause is a little mysterious.

“Electrical currents started flowing,” said Rob Stammes, of the Polarlightcenter geophysical observatory in Lofoten, Norway, in a report by Spaceweather.com.

A shockwave in magnetometer data and a surge in ground currents indicated that the magnetosphere had interacted with the interplanetary magnetic field (IMF) [Rob Stammes/Polarlightcenter/Spaceweather.com]

Stammes monitors the flow of electricity through the ground and compares it with the wiggles of the Earth’s magnetic field (as plotted above). These two key measurements allow space weather scientists to better understand how our planet’s magnetosphere is being affected by the magnetic field of our Sun and how it may impact our everyday lives.

While the Sun-Earth relationship is well studied, usually magnetospheric jiggles are associated with obvious (and often explosive) solar phenomena, such as coronal mass ejections (CMEs) and powerful solar wind flows. Yesterday, however, at around 1930 UT, our magnetosphere was jolted by a phantom event.

It was as if Earth orbited through an invisible magnetic speed bump.

Before we can understand what this means (and, indeed, why it’s important), let’s take a quick trip to the biggest magnetic dynamo in the Solar System.

As you can see, the Sun isn’t currently all that active [NASA/SDO]

You know it as the giant orb of superheated plasma that gives life to Earth and dazzles you during your commute home from work, but the Sun also has an invisible magnetic dominance over all the planets. Extending from the solar interior to well beyond the orbit of Pluto, the Sun’s magnetic field creates a vast magnetic bubble called the heliosphere. Carried by the solar wind, this magnetism spirals out, through interplanetary space, interacting with any other magnetic field it may come across. In the case of our planet, our global magnetic field (the magnetosphere) is generated by the constant sloshing of molten iron in Earth’s core. Our magnetosphere reaches out into interplanetary space and, like a forcefield, it deflects the highly energetic plasma (consisting mainly of protons and some highly ionized particles) sloughing from our Sun. There’s a constant magnetic battle raging over our heads; the Sun’s magnetic field washes over our protective magnetosphere, which acts like a sea wall protecting the coastline from an unrelenting stormy ocean.

Now, if the conditions are right, the Sun’s magnetic field may breach Earth’s magnetosphere, causing the two to snap and reconnect, effectively creating a temporary magnetic marriage between the Sun and Earth. When this happens, a magnetic highway for solar particles is formed, injecting the layers of our magnetosphere with solar plasma. Ultimately, this plasma can stream along our planet’s magnetic field (or get trapped and stored), creating auroras in higher latitudes and generate electrical currents through the atmosphere and surface.

The Earth’s magnetic field warps and bends, deflecting highly energetic solar particles. But sometimes, the shield is breached, often with dramatic effect. [NASA]

Usually, space weather forecasters use a plethora of instruments to predict when this might happen. For example, they may detect a CME erupt on the corona, predict its speed, and then register a flip in the interplanetary magnetic field (IMF) by a satellite between us and the Sun (such as NASA’s Advanced Composition Explorer, or ACE, which is located at the Sun-Earth L1 point, nearly a million miles “upstream” toward the Sun). But, in the case of yesterday’s mysterious event in Norway, there was no warning for the magnetic breach in our magnetosphere. No CME, no visible increase in solar wind intensity; just a magnetic blip from ACE and a shockwave sent ripping through magnetometer stations on the ground followed by a surge in electricity through our planet’s surface.

We’d been suckerpunched by the Sun’s magnetism, but there was no obvious fist. To confirm the sudden magnetic blow (called a geomagnetic storm), magnificent auroras erupted over the poles.

So, what happened? There is a theory:

Earth may have crossed through a fold in the heliospheric current sheet—a giant, wavy membrane of electrical current rippling through the solar system. Such crossings can cause these kind of effects.
Tony Phillips, Spaceweather.com

Looking like the warped disk of an old vinyl record, the heliospheric current sheet ripples throughout the solar system. As Earth rotates around the Sun, it will pass through the “surface” of this sheet, where the magnetic polarity of the IMF will rapidly change. And this is probably what happened yesterday. As the Earth orbited through a fold in the sheet, the magnetic polarity flipped 180 degrees, creating the phantom interaction with our magnetosphere. This, in turn, released solar particles that had been trapped in the layers of our magnetosphere, causing them to surge through the upper atmosphere, creating an intense—and surprise—auroral display.

Predicting when these events are going to occur is critical to space weather prediction efforts. As demonstrated by Stammes’ measurements of currents flowing through the ground, geomagnetic storms can overload national power grids, leaving entire nations (or, potentially, entire continents) in the dark.

While this Norway event didn’t cause reported damage to any infrastructure, it is a reminder that our planet’s interactions with the solar magnetic field—and subsequent impacts to our civilization—can be unpredictable and, in this case, invisible.

Want to Feel Good? Watch the Aurora Borealis in HD

The Aurora from Terje Sorgjerd on Vimeo.

I actually posted this jaw-dropping video on Discovery News last month, but today it got picked up on Digg, so I was reminded why I had to feature it.

The video is actually composed of 22,000 high-definition photographs, stitched together is a finely crafted time lapse video. The photographer in question is Terje Sorgjerd who braved -22C temperatures in the Arctic Circle to bring us this stunning perspective of the Aurora Borealis, or the Northern Lights. Throw in the Hans Zimmer “Gladiator” theme tune “Now We Are Free” and we get a timeless classic video that can be watched over and over again and never get bored.

So, sit back and enjoy the Sun-Earth interaction at its most spectacular.

For more of Sorgjerd’s work, check out his Facebook page.

Special thanks to my good friend Geir Barstein, science journalist at the Norwegian newspaper Dagbladet for originally writing about Sorgjerd’s work.

Screaming Exoplanets: Detecting Alien Magnetospheres

Exoplanets may reveal their location through radio emissions (NASA)

In 2009, I wrote about a fascinating idea: in the hunt for “Earth-like” exoplanets, perhaps we could detect the radio emissions from a distant world possessing a magnetosphere. This basically builds on the premise that planets in the solar system, including Earth, generate electromagnetic waves as space plasma interacts with their magnetospheres. In short, with the right equipment, could we “hear” the aurorae on extra-solar planets?

In the research I reviewed, the US Naval Research Laboratory scientist concluded that he believed it was possible, but the radio telescopes we have in operation aren’t sensitive enough to detect the crackle of distant aurorae. According to a new study presented at the RAS National Astronomy Meeting in Llandudno, Wales, on Monday, this feat may soon become a reality, not for “Earth-like” worlds but for “Jupiter-like” worlds.

“This is the first study to predict the radio emissions by exoplanetary systems similar to those we find at Jupiter or Saturn,” said Jonathan Nichols of the University of Leicester. “At both planets, we see radio waves associated with auroras generated by interactions with ionised gas escaping from the volcanic moons, Io and Enceladus. Our study shows that we could detect emissions from radio auroras from Jupiter-like systems orbiting at distances as far out as Pluto.”

Rather than looking for the magnetospheres of Earth-like worlds — thereby finding exoplanets that have a protective magnetosphere that could nurture alien life — Nichols is focusing on larger, Jupiter-like worlds that orbit their host stars from a distance. This is basically another tool in the exoplanet-hunters’ toolbox.

Over 500 exoplanets have been confirmed to exist around other stars, and another 1,200 plus exoplanetary candidates have been cataloged by the Kepler Space Telescope. The majority of the confirmed exoplanets were spotted using the “transit method” (when the exoplanet passes in front of its host star, thereby dimming its light for astronomers to detect) and the “wobble method” (when the exoplanet gravitationally tugs on its parent star, creating a very slight shift in the star’s position for astronomers to detect), but only exoplanets with short orbital periods have been spotted so far.

The more distant the exoplanet from its host star, the longer its orbital period. To get a positive detection, it’s easy to spot an exoplanet with an orbital period of days, weeks, months, or a couple of years, but what of the exoplanets with orbits similar to Jupiter (12 years), Saturn (30 years) or even Pluto (248 years!)? If we are looking for exoplanets with extreme orbits like Pluto’s, it would be several generations-worth of observations before we’d even get a hint that a world lives there.

“Jupiter and Saturn take 12 and 30 years respectively to orbit the Sun, so you would have to be incredibly lucky or look for a very long time to spot them by a transit or a wobble,” said Nichols.

By assessing how the radio emissions for a Jupiter-like exoplanet respond to its rotation rate, the quantity of material falling into the gas giant from an orbiting moon (akin Enceladus’ plumes of water ice and dust being channeled onto the gas giant) and the exoplanet’s orbital distance, Nichols has been able to identify the characteristics of a possible target star. The hypothetical, “aurora-active” exoplanet would be located between 1 to 50 AU from an ultraviolet-bright star and it would need to have a fast spin for the resulting magnetospheric activity to be detectable at a distance of 150 light-years from Earth.

What’s more, the brand new LOw Frequency ARray (LOFAR) radio telescope should be sensitive enough to detect aurorae on Jupiter-like exoplanets, even though the exoplanets themselves are invisible to other detection methods. Nice.

As we’re talking about exoplanets, magnetospheres and listening for radio signals, let’s throw in some alien-hunting for good measure: “In our Solar System, we have a stable system with outer gas giants and inner terrestrial planets, like Earth, where life has been able to evolve. Being able to detect Jupiter-like planets may help us find planetary systems like our own, with other planets that are capable of supporting life,” Nichols added.

Although Nichols isn’t talking about directly detecting habitable alien worlds (just that the detection of Jupiter-like exoplanets could reveal Solar System-like star systems), I think back to the 2009 research that discusses the direct detection of habitable worlds using this method: Aliens, if you’re out there, you can be as quiet as you like (to avoid predators), but the screaming radio emissions from your habitable planet’s magnetosphere will give away your location…

Compex Magnetic Eruption Witnessed by Solar Observatories

sunnow — Solar Dynamics Observatory view of the solar disk shortly after eruption (NASA).

This morning, at 08:55 UT, NASA’s Solar Dynamics Observatory (SDO) detected a C3-class flare erupt inside a sunspot cluster. 100,000 kilometers away, deep within the solar atmosphere (the corona), an extended magnetic field filled with cool plasma forming a dark ribbon across the face of the sun (a feature known as a “filament”) erupted at the exact same time.

It seems very likely that both events were connected after a powerful shock wave produced by the flare destabilized the filament, causing the eruption.

A second solar observatory, the Solar and Heliospheric Observatory (SOHO), then spotted a huge coronal mass ejection (CME) blast into space, straight in the direction of Earth. Solar physicists have calculated that this magnetic bubble filled with energetic particles should hit Earth on August 3, so look out for some intense aurorae, a solar storm is on its way…

For more on this impressive solar eruption, read my Discovery News article, “Incoming! The Sun Unleashes CME at Earth“

Awesome.

104078907 — The Moon, Space Shuttle Atlantis, an aurora plus Kibo, all in one breathtaking scene (Soichi Noguchi)

The instant I saw this photograph I realized I was seeing something so beautiful, I’d have a hard job writing something to accompany it.

Coming straight from the Twitter feed of Soichi Noguchi, Japanese astronaut and social-media-in-space-photography-guru, this single photograph has captured the moon, an aurora hanging above the Earth’s limb, a docked space shuttle Atlantis and the International Space Station’s Kibo module (plus a bonus robotic arm and solar panel).

This picture is awesome on so many levels. And to be honest, this should be the photograph of Atlantis’ final mission. It encapsulates so much; a testament to what mankind is capable of and a tribute to the men and women who are currently in space, risking their lives for the advancement of our race.

There’s not much else to say, except: wow.

Black Holes, Aurorae and the Event Horizon Telescope

black-hole-aurora — My impression as to how a black hole 'aurora' might look like near an event horizon (Ian O'Neill/Discovery News)

Usually, aurorae happen when the solar wind blasts the Earth’s atmosphere. However, black holes may also have a shot at producing their very own northern lights. What’s more, we might even be able to observe this light display in the future.

Accretion Disks and Magnetic Fields

Simulating a rapidly spinning black hole, two researchers from Japan modeled an accretion disk spinning with it.

Inside this disk would be superheated plasma and as it rotates it might act like a dynamo, charged particles generating a magnetic field looping through the disk. But this magnetic field wont stay confined to the disk for long. Due to inertial effects, the magnetic field would be dragged into the event horizon, causing the magnetic fieldlines to ‘attach’ themselves to the black hole.

Assuming the accretion disk continues to generate a continuous magnetic field, a global black hole ‘magnetosphere’ would result.

bh-sch — A diagram of the black hole's magnetosphere (Takahashi and Takahashi, 2010)

A Plasma Hosepipe

As you’ve probably seen in the striking imagery coming from the high-definition movies being produced by the Solar Dynamics Observatory, magnetic fieldlines close to the solar surface can fill with solar plasma, creating bright coronal loops. This hot plasma fills the loops, feeding around the magnetic field like a hosepipe filling with water.

The same principal would apply to the black hole’s magnetosphere: the looped magnetic field feeding from the accretion disk to the event horizon filling with plasma as it is sucked out of the disk (by the black hole’s dominating gravitational field).

As you’d expect, the plasma will fall into the black hole at relativistic speeds, converted into pure energy, blasting with intense radiation. However, the Japanese researchers discovered something else that may happen just before the plasma is destroyed by the black hole: it will generate a shock.

As predicted by the model, this shock will form when the plasma exceeds the local Alfven speed. For want of a better analogy, this is like a supersonic jet creating a sonic boom. But in the plasma environment, as the plasma flow hits the shock front, it will rapidly decelerate, dumping energy before continuing to rain down on the event horizon. This energy dump will be converted into heat and radiation.

This fascinating study even goes so far as predicting the configuration of the black hole magnetosphere, indicating that the radiation generated by the shock would form two halos sitting above the north and south ‘poles’ of the black hole. From a distance, these halos would look like aurorae.

Very Large Baseline Interferometry

So there you have it. From a spinning black hole’s accretion disk to shocked plasma, a black hole can have an aurora. The black hole aurora, however, would be generated by shocked plasma, not plasma hitting atmospheric gases (as is the case on Earth).

This all sounds like a fun theoretical idea, but it may also have a practical application in the not-so-distant future.

Last year, I wrote “The Event Horizon Telescope: Are We Close to Imaging a Black Hole?” which investigated the efforts under way in the field of very large baseline interferometry (or “VLBI”) to directly observe the supermassive black hole (Sagittarius A*) living in the center of our galaxy.

In a paper written by Vincent Fish and Sheperd Doeleman at the MIT Haystack Observatory, results from a simulation of several radio telescopes as part of an international VLBI campaign were detailed. The upshot was that the more radio antennae involved in such a campaign, the better the resolution of the observations of the ‘shadow’ of the black hole’s event horizon.

If the black hole’s event horizon could be observed by a VLBI campaign, could its glowing aurorae also be spotted? Possibly.

For more, check out my Discovery News article: “Can a Black Hole Have an ‘Aurora’?” and my Astroengine.com article: “The Event Horizon Telescope: Are We Close to Imaging a Black Hole?“

Standing Under the Aurora

Under an auroal display in 2004 above a Harstad (Norway) communications tower (NASA) — Under an auroal display in 2004 above a Harstad (Norway) communications tower (Frank Andreassen/NASA)

In 2002, I remember standing on the ice-crusted snow in Svalbard, looking up, in awe of what I was seeing. Dancing overhead, stretching from horizon to horizon was my first aurora. Predominantly green and highly structured against the inky black 24 hour night, the highly dynamic plasma danced, much like a curtain in the wind. Occasionally, I would see the ribbons of green scatter, forming a radiant pattern, much like today’s NASA Astronomy Picture of the Day (APOD), above.

Seven years ago, I was studying the interaction between the solar wind and the Earth’s upper polar atmosphere with four friends for five months at The University Centre in Svalbard, and it is an experience I’ll never forget. Seeing this dazzling view from a communications tower in northern Norway stirs some amazing memories of my stay on this unique island in the high arctic, watching the light generated as the solar plasma spiralled down Earth’s magnetic field, interacting with our atmosphere.

From that magical day onward, I never underestimated the beauty of physics again…

A Mystery Aurora above Saturn’s Mysterious North Pole Hexagon

Not only does Saturn have a mysterious hexagonal shape etched into the bands of cloud above its north pole, it also has a unique magnetic structure. This is suggested by recent results recorded by the NASA Cassini probe that passed over the pole to see a huge active auroral region, much larger and more dynamic than expected. Interestingly, the NASA press release has not linked the strange aurora with the long-lived hexagonal shape in the gas giant’s atmosphere. Could the hexagon be formed by a unique magnetic structure above Saturn? Or could both phenomena be connected in some other way?
Continue reading “A Mystery Aurora above Saturn’s Mysterious North Pole Hexagon”