Tag Archives: magnetosphere

We’ve just discovered the Earth’s largest drum: our planet’s magnetosphere

A new study found that the Earth’s magnetic shield beats like a drum when it’s hit by external impulses. This confirms a decades-old theory

Artist rendition of a plasma jet impact (yellow) generating standing waves at the magnetopause boundary (blue) and in the magnetosphere (green). The outer group of four THEMIS probes witnessed the flapping of the magnetopause over each satellite in succession, confirming the expected behavior/frequency of the theorized magnetopause eigenmode wave. Image credits: E. Masongsong/UCLA, M. Archer/QMUL, H. Hietala/UTU.

The Earth’s magnetic field is driven by convection currents in the Earth’s outer core. Differences in temperature, pressure, and composition within the outer core cause some parts of the core to move around. The flow of this liquid iron generates electric currents, which in turn produce magnetic fields. The resulting magnetic fields produce further electric currents, which then generate their own magnetic fields, and so on. This natural self-sustaining loop is called a geodynamo, and produces a magnetic field that loops around the entire planet.

This magnetosphere is essential for life on Earth, as it protects the atmosphere from being eroded by the solar wind and deflects cosmic rays (high-energy charged particles that are mostly from outside the Solar System). However, we’re still learning a lot about the magnetosphere. Obviously, no one has gone down to the inner core to actually see how it is formed, and measurements of its overall structure remain challenging. In a new paper, researchers describe a feature of this field which had been predicted mathematically 40 years ago, but never previously observed.

Essentially, when an impulse strikes the outer boundary of the magnetopause, ripples can travel along its surface. These then get reflected back when they approach the magnetic poles. It’s a bit like how acoustic waves are absorbed and reflected by a drum. When the impulse interacts with the Earth’s magnetosphere, the interference the waves leads to a standing wave pattern in which specific points appear to be standing still while others vibrate back and forth — it’s exactly the way a drum resonates when struck.

Dr. Martin Archer, a space physicist at Queen Mary University of London and lead author of the paper, explains:

“There had been speculation that these drum-like vibrations might not occur at all, given the lack of evidence over the 45 years since they were proposed. Another possibility was that they are just very hard to definitively detect.”

“Earth’s magnetic shield is continuously buffeted with turbulence so we thought that clear evidence for the proposed booming vibrations might require a single sharp hit from an impulse. You would also need lots of satellites in just the right places during this event so that other known sounds or resonances could be ruled out. The event in the paper ticked all those quite strict boxes and at last, we’ve shown the boundary’s natural response,” said Archer.

In order to finally prove this theory, researchers used data from five NASATHEMIS satellites, designed specifically to study the magnetosphere. These five satellites were ideally located when a strong isolated plasma jet slammed into the magnetopause.

The probes were able to detect the boundary’s oscillations and the resulting sounds within the Earth’s magnetic shield, which confirmed the drum model and ruled out any alternative explanations

The Earth isn’t alone in having a magnetosphere. Other planets like Mercury, Jupiter and Saturn, have also been found to have similar magnetic shield — which means that drum-like vibrations may be possible elsewhere. However, further research is needed to understand just how often these vibrations occur and what their significance is.

Movements of the magnetopause can have wide-ranging effects on space weather, potentially damaging technology like power grids, GPS, and even passenger airlines.

Journal Reference: ‘Direct Observations Of A Surface Eigenmode Of The Dayside Magnetopause’. Archer et al. Nature Communications.

For the first time, scientists directly observe how Northern Lights are formed

With the advent of new satellite technology, researchers have confirmed the theories behind this impressive phenomenon.

When it comes to natural shows, it doesn’t get much better than the Northern Lights. This dazzling light show was admired by humans since the beginning of time, but scientists still haven’t been able to fully confirm theories about its formation — until now. For the first time, geophysicists at the University of Tokyo have directly observed the underlying mechanisms causing the Northern Lights, thereby confirming long-held theories about their formation.

“Auroral substorms … are caused by global reconfiguration in the magnetosphere, which releases stored solar wind energy,” writes lead author Satoshi Kasahara, an associate professor in the Department of Earth and Planetary Science at the Graduate School of Science of the University of Tokyo in Japan, the lead author of the paper. “They are characterized by auroral brightening from dusk to midnight, followed by violent motions of distinct auroral arcs that eventually break up, and emerge as diffuse, pulsating auroral patches at dawn.”

The spectacular light show starts with a type of plasma wave called chorus waves. The magnetic reconfiguration can cause these chorus waves to rain electrons into the upper atmosphere. This balances the system, but in the process, gives off colorful lights as electrons fall into the atmosphere.

The scattered electrons precipitate into the atmosphere resulting in auroral illumination. Intermittent occurrence of chorus waves and associated electron scattering leads to auroral pulsation. Image credits: The 2018 ERG science team.

It’s been the leading theory for sometime, but there were still question about whether these chorus waves have enough energy to produce the auroras. Now, researchers have finally caught them in the act.

“We, for the first time, directly observed scattering of electrons by chorus waves generating particle precipitation into the Earth’s atmosphere,” Kasahara said. “The precipitating electron flux was sufficiently intense to generate pulsating aurora.”

They were able to observe this phenomenon thanks to a new type of equipment. Generally, electron sensors cannot distinguish the precipitating electrons of other types, so Kasahara and his team developed a new sensor that can observe the interactions between electrons and chorus waves. The sensor was fitted aboard the Exploration of energization and Radiation in Geospace (ERG) satellite launched by the Japan Aerospace Exploration Agency in December 2016.

A full understanding of all the physical processes involved in the creation of different types of auroras is still incomplete, but the pieces are starting to fall into place. Researchers will now use the ERG satellite to understand other phenomena associated with the magnetosphere.

Journal Reference: S. Kasahara at al. Pulsating aurora from electron scattering by chorus waves. Nature, 2018; 554 (7692): 337 DOI: 10.1038/nature25505

Artist's conception of the complex magnetic field environment at Mars. Yellow lines represent magnetic field lines from the Sun carried by the solar wind, blue lines represent Martian surface magnetic fields, white sparks are reconnection activity, and red lines are reconnected magnetic fields that link the surface to space via the Martian magnetotail. Credit: Anil Rao/Univ. of Colorado/MAVEN/NASA GSFC.

NASA discovers Mars has a magnetic tail twisted by solar wind

Artist's conception of the complex magnetic field environment at Mars. Yellow lines represent magnetic field lines from the Sun carried by the solar wind, blue lines represent Martian surface magnetic fields, white sparks are reconnection activity, and red lines are reconnected magnetic fields that link the surface to space via the Martian magnetotail. Credit: Anil Rao/Univ. of Colorado/MAVEN/NASA GSFC.

Artist’s conception of the complex magnetic field environment at Mars. Yellow lines represent magnetic field lines from the Sun carried by the solar wind, blue lines represent Martian surface magnetic fields, white sparks are reconnection activity, and red lines are reconnected magnetic fields that link the surface to space via the Martian magnetotail. Credit: Anil Rao/Univ. of Colorado/MAVEN/NASA GSFC.

Mars has a unique magnetotail found nowhere else in the solar system, NASA scientists report. According to the data gathered by the Mars Atmosphere and Volatile Evolution Mission (MAVEN) spacecraft, currently orbiting the Red Planet, this intriguing invisible magnetic tail is twisted by the interaction with solar wind. Studying this rare phenomenon could fill in the blanks in our understanding of how Mars went from a flourishing, wet world to a barren wasteland.

Tail in the solar wind

Here on Earth, the motion of molten iron alloys in its outer core acts like a geodynamo which generates a massive magnetic field. Scientists call our planet’s magnetic field the magnetosphere. It extends for several tens of thousands of kilometers into space, well above the atmosphere, sheltering the planet from charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer that protects the Earth from harmful ultraviolet radiation.

Earth isn’t unique in this respect. Jupiter has masses of liquid metallic hydrogen in its outer mantle, creating the largest planetary magnetic field in the solar system. Uranus generates a global magnetosphere closer to the surface, which leads to some very strange quadrupole field effects —  rather than just a north and a south, there are another two poles lurking in a quadrupole field. Mars also used to have a magnetic field but lost it half a billion years after its formation.

Scientists aren’t sure how the red planet lost its magnetosphere but there are currently two leading theories. The first says that its core shut down, deactivating the dynamo and consequently Mars’ global magnetic field. The other leading hypothesis suggests that massive heat generated by large asteroid impacts warmed the outer layer of the planet to such a degree that it shut down convection from the hot core to the mantle.

After Mars’ lost its magnetic field, the atmosphere soon followed. With nothing to shelter it from cosmic rays and solar storms, the atmosphere thinned to the point that it’s now roughly 100 times less dense than Earth’s atmosphere. Mars is still continuously losing its atmosphere.

Nowadays, solar wind mostly comprised of protons strikes Mars at about 1,000,000 mph, moving so quickly that it flings atmospheric particles. Presently, Mars loses about 100 grams of atmospheric gas every second.

According to NASA scientists, there are still some remnant so-called ‘fossil’ magnetic fields embedded in certain features of the red planet’s surface. Instruments onboard MAVEN collected data that suggest the planet has a magnetotail formed when magnetic fields carried by solar wind interact with the fossil magnetic fields in a process called magnetic reconnection. For the two magnetic fields to join in magnetic reconnection, the solar wind field needs to be oriented in the opposite direction to that of the patchwork magnetic fields from Mars.

“We found that Mars’ magnetic tail, or magnetotail, is unique in the solar system,” said Gina DiBraccio of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a public statement. “It’s not like the magnetotail found at Venus, a planet with no magnetic field of its own, nor is it like Earth’s, which is surrounded by its own internally generated magnetic field. Instead, it is a hybrid between the two.”

Since MAVEN continually changes its orbit orientation with respect to the Sun, the spacecraft took measurements covering a wide range of Martian surface features. NASA scientists then used this valuable data to plot a map of the Martian magnetotail and its interaction with the solar wind. The scientists then designed a model that predicts the magnetic reconnection and compared their results with the live data. The theoretical and experimental data were in agreement suggesting the Martian magnetotail twists “45 degrees from what’s expected based on the direction of the magnetic field carried by the solar wind,” said DiBraccio.

Next, NASA plans to use other instruments deployed by MAVEN, this time to generate an ‘escaping particles’ map. The goal is to see whether or not reconnection is contributing to Martian atmospheric loss and how significant this effect is.

“Mars is really complicated but really interesting at the same time,” said DiBraccio.

Uranus has a magnetosphere that turns on and off every day

The magnetosphere on Uranus is not in sync with the planet’s rotation, causing it to switch off sometimes.

Uranus as a featureless disc, photographed by Voyager 2 in 1986.

Although it’s been 30 years since Voyager 2 sped past Uranus, we’re still analyzing the data and learning new things about the planet. This time, it’s about the planet’s magnetosphere.

A geometric nightmare

The magnetosphere is basically a region of space surrounding a planet (or any object), in which charged particles are controlled by that object’s magnetic field. In a planet like Earth, the magnetosphere is crucial because is mitigates or even blocks the negative effects of cosmic radiation. But on Earth, the magnetic field is nearly perfectly aligned with the spin axis, meaning that the same alignment of Earth’s magnetosphere is always facing toward the sun. In turn, this means that the magnetic field threaded in the ever-present solar wind must change direction in order to reconfigure Earth’s field from closed to open. This frequently occurs with strong solar storms. But our planet is privileged, and not the same can be said about Uranus.

The gas giant spins on its side and has a lopsided magnetic field, tilted by 60 degrees. So the magnetic field also tumbles asymmetrically relative to the solar wind direction. Since Uranus spins quite quickly (taking 17.24 hours to complete a full rotation), this leads to a periodic open-close-open-close scenario as it tumbles through the solar wind, leaving wide gaps open — like chinks in the planet’s magnetic defense. If that’s hard to picture… well, it is.

“Uranus is a geometric nightmare,” said Carol Paty, the Georgia Tech associate professor who co-authored the study. “The magnetic field tumbles very fast, like a child cartwheeling down a hill head over heels. When the magnetized solar wind meets this tumbling field in the right way, it can reconnect and Uranus’ magnetosphere goes from open to closed to open on a daily basis.”

Artistic depiction of the Earth’s magnetosphere. Image via Wiki Commons.

At this moment, we don’t know if Uranus is a typical case and the Earth is the odd one out, if it’s the other way around, or if there’s some innate characteristic of the planets that determine how the magnetosphere behaves. Understanding Uranus might serve as a stepping stone to understanding other planets outside our solar system — but unfortunately, the Voyager data is all we have.

“The majority of exoplanets that have been discovered appear to also be ice giants in size,” said Xin Cao, the Georgia Tech Ph.D. candidate in earth and atmospheric sciences who led the study. “Perhaps what we see on Uranus and Neptune is the norm for planets: very unique magnetospheres and less-aligned magnetic fields. Understanding how these complex magnetospheres shield exoplanets from stellar radiation is of key importance for studying the habitability of these newly discovered worlds.”

Journal Reference: Xin Cao, Carol Paty — Diurnal and seasonal variability of Uranus’s magnetosphere. DOI: 10.1002/2017JA024063.

The Radiation Belt Storm Probes are on a two-year mission to explore the Van Allen Belts. (c) NASA

How Earth sounds like from outer space

The Radiation Belt Storm Probes are on a two-year mission to explore the Van Allen Belts. (c) NASA

The Radiation Belt Storm Probes are on a two-year mission to explore the Van Allen Belts. (c) NASA

Surrounding our planet are rings of plasma, part of Earth’s magnetosphere, which are pulsing with radio waves. These aren’t audible to the human ear, but radio dishes and antennas always pick them up. Recently, NASA scientists recorded some of the Earth’s pulses and transformed them into acoustic waves – the end result is a short song chanted by our very planet.

Dubbed “Chorus”, the song is made of radio waves that oscillate at acoustic frequencies, between 0 and 10 kHz. Actually, similar sounds are often picked up by ham radio operators on Earth. You can listen to it in the player embedded below.

“Chorus emissions are front and center for the Storm Probe mission,” says Craig Kletzing of the University of Iowa. “They are thought to be one of the most important waves for energizing the electrons that make up the outer radiation belt.”

The sounds were picked up by the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on NASA’s recently launched Radiation Belt Storm Probes. The two probes are orbiting inside the radiation belts, sampling electromagnetic fields, counting the number of energetic particles, and listening to plasma waves of many frequencies. Though usually harmless, sometimes high-energy particles can endanger both satellites and astronauts.

source: NASA