At a closest average distance of 41 million km (25,476,219 mi), Venus is the closest planet to Earth. Credit: NASA/JPL/Magellan
For many reasons, Venus is sometimes referred to as “Earth’s Twin” (or “Sister Planet”, depending on who you ask). Like Earth, it is terrestrial (i.e. rocky) in nature, composed of silicate minerals and metals that are differentiated between an iron-nickel core and silicate mantle and crust. But when it comes to their respective atmospheres and magnetic fields, our two planets could not be more different.
For some time, astronomers have struggled to answer why Earth has a magnetic field (which allows it to retain a thick atmosphere) and Venus do not. According to a new study conducted by an international team of scientists, it may have something to do with a massive impact that occurred in the past. Since Venus appears to have never suffered such an impact, its never developed the dynamo needed to generate a magnetic field.
The study, titled “Formation, stratification, and mixing of the cores of Earth and Venus“, recently appeared in the scientific journal Earth and Science Planetary Letters. The study was led by Seth A. Jacobson of Northwestern University, and included members from the Observatory de la Côte d’Azur, the University of Bayreuth, the Tokyo Institute of Technology, and the Carnegie Institution of Washington.
The Earth’s layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com
For the sake of their study, Jacobson and his colleagues began considering how terrestrial planets form in the first place. According to the most widely-accepted models of planet formation, terrestrial planets are not formed in a single stage, but from a series of accretion events characterized by collisions with planetesimals and planetary embryos – most of which have cores of their own.
Recent studies on high-pressure mineral physics and on orbital dynamics have also indicated that planetary cores develop a stratified structure as they accrete. The reason for this has to do with how a higher abundance of light elements are incorporated in with liquid metal during the process, which would then sink to form the core of the planet as temperatures and pressure increased.
Such a stratified core would be incapable of convection, which is believed to be what allows for Earth’s magnetic field. What’s more, such models are incompatible with seismological studies that indicate that Earth’s core consists mostly of iron and nickel, while approximately 10% of its weight is made up of light elements – such as silicon, oxygen, sulfur, and others. It’s outer core is similarly homogeneous, and composed of much the same elements.
As Dr. Jacobson explained to Universe Today via email:
“The terrestrial planets grew from a sequence of accretionary (impact) events, so the core also grew in a multi-stage fashion. Multi-stage core formation creates a layered stably stratified density structure in the core because light elements are increasingly incorporated in later core additions. Light elements like O, Si, and S increasingly partition into core forming liquids during core formation when pressures and temperatures are higher, so later core forming events incorporate more of these elements into the core because the Earth is bigger and pressures and temperatures are therefore higher.
“This establishes a stable stratification which prevents a long-lasting geodynamo and a planetary magnetic field. This is our hypothesis for Venus. In the case of Earth, we think the Moon-forming impact was violent enough to mechanically mix the core of the Earth and allow a long-lasting geodynamo to generate today’s planetary magnetic field.”
To add to this state of confusion, paleomagnetic studies have been conducted that indicate that Earth’s magnetic field has existed for at least 4.2 billion years (roughly 340 million years after it formed). As such, the question naturally arises as to what could account for the current state of convection and how it came about. For the sake of their study, Jacobson and his team considering the possibility that a massive impact could account for this. As Jacobson indicated:
“Energetic impacts mechanically mix the core and so can destroy stable stratification. Stable stratification prevents convection which inhibits a geodynamo. Removing the stratification allows the dynamo to operate.”
Basically, the energy of this impact would have shaken up the core, creating a single homogeneous region within which a long-lasting geodynamo could operate. Given the age of Earth’s magnetic field, this is consistent with the Theia impact theory, where a Mars-sized object is believed to have collided with Earth 4.51 billion years ago and led to the formation of the Earth-Moon system.
This impact could have caused Earth’s core to go from being stratified to homogeneous, and over the course of the next 300 million years, pressure and temperature conditions could have caused it to differentiate between a solid inner core and liquid outer core. Thanks to rotation in the outer core, the result was a dynamo effect that protected our atmosphere as it formed.
Artist’s concept of a collision between proto-Earth and Theia, believed to happened 4.5 billion years ago. Credit: NASA
The seeds of this theory were presented last year at the 47th Lunar and Planetary Science Conference in The Woodlands, Texas. During a presentation titled “Dynamical Mixing of Planetary Cores by Giant Impacts“, Dr. Miki Nakajima of Caltech – one of the co-authors on this latest study – and David J. Stevenson of the Carnegie Institution of Washington. At the time, they indicated that the stratification of Earth’s core may have been reset by the same impact that formed the Moon.
It was Nakajima and Stevenson’s study that showed how the most violent impacts could stir the core of planets late in their accretion. Building on this, Jacobson and the other co-authors applied models of how Earth and Venus accreted from a disk of solids and gas about a proto-Sun. They also applied calculations of how Earth and Venus grew, based on the chemistry of the mantle and core of each planet through each accretion event.
The significance of this study, in terms of how it relates to the evolution of Earth and the emergence of life, cannot be understated. If Earth’s magnetosphere is the result of a late energetic impact, then such impacts could very well be the difference between our planet being habitable or being either too cold and arid (like Mars) or too hot and hellish (like Venus). As Jacobson concluded:
“Planetary magnetic fields shield planets and life on the planet from harmful cosmic radiation. If a late, violent and giant impact is necessary for a planetary magnetic field then such an impact may be necessary for life.”
Looking beyond our Solar System, this paper also has implications in the study of extra-solar planets. Here too, the difference between a planet being habitable or not may come down to high-energy impacts being a part of the system’s early history. In the future, when studying extra-solar planets and looking for signs of habitability, scientists may very well be forced to ask one simple question: “Was it hit hard enough?”
Artist's depiction with cutaway section of the two giant donuts of radiation, called the Van Allen Belts, that surround Earth. Credit: NASA
Human beings have known for quite some time that our behavior has a significant influence on our planet. In fact, during the 20th century, humanity’s impact on the natural environment and climate has become so profound that some geologists began to refer to the modern era as the “Anthropocene”. In this age, human agency is the most deterministic force on the planet.
But according to a comprehensive new study by an Anglo-American team of researchers, human beings might be shaping the near-space environment as well. According to the study, radio communications, EM radiation from nuclear testing and other human actions have led to the creation of a barrier around Earth that is shielding it against high-energy space radiation.
The study, which was published in the journal Space Science Reviews under the title “Anthropogenic Space Weather“, was conducted by a team of scientists from the US and Imperial College, London. Led by Dr. Tamas Gombosi, a professor at the University of Michigan and the director at the Center for Space Modelling, the team reviewed the impact anthropogenic processes have on Earth’s near-space environment.
These processes include VLF and radio-frequency (RF) radio communications, which began in earnest during the 19th century and grew considerably during the 20th century. Things became more intense during the 1960s when the United States and the Soviet Union began conducting high-altitude nuclear tests, which resulted in massive electromagnetic pulses (EMP) in Earth’s atmosphere.
To top it off, the creation of large-scale power grids has also had an impact on the near-space environment. As they state in their study:
“The permanent existence, and growth, of power grids and of VLF transmitters around the globe means that it is unlikely that Earth’s present-day space environment is entirely “natural” – that is, that the environment today is the environment that existed at the onset of the 19th century. This can be concluded even though there continue to exist major uncertainties as to the nature of the physical processes that operate under the influence of both the natural environment and the anthropogenically-produced waves.”
The existence of radiation belts (or “toroids”) around Earth has been a well-known fact since the late 1950s. These belts were found to be the result of charged particles coming from the Sun (i.e. “solar wind”) that were captured by and held around Earth by it’s magnetic field. They were named Van Allen Radiation Belts after their discover, the American space scientist James Van Allen.
The twin Radiation Belt Storm Probes, later renamed the Van Allen Probes. Credit: NASA/JHUAPL
The extent of these belts, their energy distribution and particle makeup has been the subject of multiple space missions since then. Similarly, studies began to be mounted around the same time to discover how human-generated charged particles, which would interact with Earth’s magnetic fields once they reached near-space, could contribute to artificial radiation belts.
However, it has been with the deployment of orbital missions like the Van Allen Probes (formerly the Radiation Belt Storm Probes) that scientists have been truly able to study these belts. In addition to the aforementioned Van Allen Belts, they have also taken note of the VLF bubble that radio transmissions have surrounded Earth with. As Phil Erickson, the assistant director at the MIT Haystack Observatory, said in a NASA press release:
“A number of experiments and observations have figured out that, under the right conditions, radio communications signals in the VLF frequency range can in fact affect the properties of the high-energy radiation environment around the Earth.”
One thing that the probes have noticed was the interesting way that the outward extent of the VLF bubble corresponds almost exactly to the inner and outer Van Allen radiation belts. What’s more, comparisons between the modern extent of the radiations belts from the Van Allen Probe data shows that the inner boundary is much farther away than it appeared to be during the 1960s (when VLF transmissions were lower).
Two giant belts of radiation surround Earth. The inner belt is dominated by protons and the outer one by electrons. Credit: NASA
What this could mean is that the VLF bubble we humans have been creating for over a century and half has been removing excess radiation from the near-Earth environment. This could be good news for us, since the effects of charged particles on electronics and human health is well-documented. And during periods of intense space weather – aka. solar flares – the effects can be downright devastating.
Given the opportunity for further study, we may find ways to predictably and reliably use VLF transmissions to make the near-Earth environment more human and electronics-friendly. And with companies like SpaceX planning on bringing internet access to the world through broadband internet-providing satellites, and even larger plans for the commercialization of Near-Earth Orbit, anything that can mitigate the risk posed by radiation is welcome.
And be sure to check this video that illustrates the Van Allen Probes findings, courtesy of NASA:
At one time, Mars had a magnetic field similar to Earth, which prevented its atmosphere from being stripped away. Credit: NASA
In the past few decades, astronomers and geophysicists have benefited immensely from the study of planetary magnetic fields. Dedicated to mapping patterns of magnetism on other astronomical bodies, this field has grown thanks to missions ranging from the Voyager probes to the more recent Mars Atmosphere and Volatile EvolutioN (MAVEN) mission.
Looking ahead, it is clear that this field of study will play a vital role in the exploration of the Solar System and beyond. As Jared Espley of NASA’s Goddard Space Flight Center outlined during a presentation at NASA’s Planetary Science Vision 2050 Workshop, these goals include advancing human exploration of the cosmos and the search for extraterrestrial life.
Artist's conception of a terraformed Mars. Credit: Ittiz/Wikimedia Commons
This week, NASA’s Planetary Science Division (PSD) hosted a community workshop at their headquarters in Washington, DC. Known as the “Planetary Science Vision 2050 Workshop“, this event ran from February 27th to March 1st, and saw scientists and researchers from all over the world descend on the capitol to attend panel discussions, presentations, and talks about the future of space exploration.
One of the more intriguing presentations took place on Wednesday, March 1st, where the exploration of Mars by human astronauts was discussed. In the course of the talk, which was titled “A Future Mars Environment for Science and Exploration“, Director Jim Green discussed how deploying a magnetic shield could enhance Mars’ atmosphere and facilitate crewed missions there in the future.
The current scientific consensus is that, like Earth, Mars once had a magnetic field that protected its atmosphere. Roughly 4.2 billion years ago, this planet’s magnetic field suddenly disappeared, which caused Mars’ atmosphere to slowly be lost to space. Over the course of the next 500 million years, Mars went from being a warmer, wetter environment to the cold, uninhabitable place we know today.
Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet’s upper atmosphere. Credits: NASA/GSFC
This theory has been confirmed in recent years by orbiters like the ESA’s Mars Express and NASA’s Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), which have been studying the Martian atmosphere since 2004 and 2014, respectively. In addition to determining that solar wind was responsible for depleting Mars’ atmosphere, these probes have also been measuring the rate at which it is still being lost today.
Without this atmosphere, Mars will continue to be a cold, dry place where life cannot flourish. In addition to that, future crewed mission – which NASA hopes to mount by the 2030s – will also have to deal with some severe hazards. Foremost among these will be exposure to radiation and the danger of asphyxiation, which will pose an even greater danger to colonists (should any attempts at colonization be made).
In answer to this challenge, Dr. Jim Green – the Director of NASA’s Planetary Science Division – and a panel of researchers presented an ambitious idea. In essence, they suggested that by positioning a magnetic dipole shield at the Mars L1 Lagrange Point, an artificial magnetosphere could be formed that would encompass the entire planet, thus shielding it from solar wind and radiation.
Naturally, Green and his colleagues acknowledged that the idea might sounds a bit “fanciful”. However, they were quick to emphasize how new research into miniature magnetospheres (for the sake of protecting crews and spacecraft) supports this concept:
“This new research is coming about due to the application of full plasma physics codes and laboratory experiments. In the future it is quite possible that an inflatable structure(s) can generate a magnetic dipole field at a level of perhaps 1 or 2 Tesla (or 10,000 to 20,000 Gauss) as an active shield against the solar wind.”
The proposed method for creating an artificial magnetic dipole at Mars’ L1 Lagrange Point. Credit: NASA/J.Green
In addition, the positioning of this magnetic shield would ensure that the two regions where most of Mars’ atmosphere is lost would be shielded. In the course of the presentation, Green and the panel indicated that these the major escape channels are located, “over the northern polar cap involving higher energy ionospheric material, and 2) in the equatorial zone involving a seasonal low energy component with as much as 0.1 kg/s escape of oxygen ions.”
To test this idea, the research team – which included scientists from Ames Research Center, the Goddard Space Flight Center, the University of Colorado, Princeton University, and the Rutherford Appleton Laboratory – conducted a series of simulations using their proposed artificial magnetosphere. These were run at the Coordinated Community Modeling Center (CCMC), which specializes in space weather research, to see what the net effect would be.
What they found was that a dipole field positioned at Mars L1 Lagrange Point would be able to counteract solar wind, such that Mars’ atmosphere would achieve a new balance. At present, atmospheric loss on Mars is balanced to some degree by volcanic outpassing from Mars interior and crust. This contributes to a surface atmosphere that is about 6 mbar in air pressure (less than 1% that at sea level on Earth).
As a result, Mars atmosphere would naturally thicken over time, which lead to many new possibilities for human exploration and colonization. According to Green and his colleagues, these would include an average increase of about 4 °C (~7 °F), which would be enough to melt the carbon dioxide ice in the northern polar ice cap. This would trigger a greenhouse effect, warming the atmosphere further and causing the water ice in the polar caps to melt.
At one time, Mars had a magnetic field similar to Earth, which prevented its atmosphere from being stripped away. Credit: NASA
By their calculations, Green and his colleagues estimated that this could lead to 1/7th of Mars’ oceans – the ones that covered it billions of years ago – to be restored. If this is beginning to sound a bit like a lecture on how to terraform Mars, it is probably because these same ideas have been raised by people who advocating that very thing. But in the meantime, these changes would facilitate human exploration between now and mid-century.
“A greatly enhanced Martian atmosphere, in both pressure and temperature, that would be enough to allow significant surface liquid water would also have a number of benefits for science and human exploration in the 2040s and beyond,” said Green. “Much like Earth, an enhanced atmosphere would: allow larger landed mass of equipment to the surface, shield against most cosmic and solar particle radiation, extend the ability for oxygen extraction, and provide “open air” greenhouses to exist for plant production, just to name a few.”
These conditions, said Green and his colleagues, would also allow for human explorers to study the planet in much greater detail. It would also help them to determine the habitability of the planet, since many of the signs that pointed towards it being habitable in the past (i.e. liquid water) would slowly seep back into the landscape. And if this could be achieved within the space of few decades, it would certainly help pave the way for colonization.
In the meantime, Green and his colleagues plan to review the results of these simulations so they can produce a more accurate assessment of how long these projected changes would take. It also might not hurt to conduct some cost-assessments of this magnetic shield. While it might seem like something out of science fiction, it doesn’t hurt to crunch the numbers!
Stay tuned for more stories from the Planetary Science Vision 2050 Workshop!
The Earth's layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com
Whether or not a planet has a magnetic field goes a long way towards determining whether or not it is habitable. Whereas Earth has a strong magnetosphere that protects life from harmful radiation and keeps solar wind from stripping away its atmosphere, planet’s like Mars no longer do. Hence why it went from being a world with a thicker atmosphere and liquid water on its surface to the cold, desiccated place it is today.
For this reason, scientists have long sought to understand what powers Earth’s magnetic field. Until now, the consensus has been that it was the dynamo effect created by Earth’s liquid outer core spinning in the opposite direction of Earth’s rotation. However, new research from the Tokyo Institute of Technology suggests that it may actually be due to the presence of crystallization in the Earth’s core.
The research was conducted by scientists from the Earth-Life Science Institute (ELSI) at Tokyo Tech. According to their study – titled “Crystallization of Silicon Dioxide and Compositional Evolution of the Earth’s Core“, which appeared recently in Nature – the energy that drives the Earth’s magnetic field may have more to do with the chemical composition of the Earth’s core.
Using a diamond anvil and a laser, researchers at Tokyo Tech subjected silicon and oxygen samples to conditions similar to the Earth’s core. Credit: Sang-Heon Shim/Arizona State University
Of particular concern for the research team was the rate of which Earth’s core cools over geological time – which has been the subject of debate for some time. And for Dr. Kei Hirose – the director of the Earth-Life Science Institute and lead author on the paper – it has been something of a lifelong pursuit. In a 2013 study, he shared research findings that indicated how the Earth’s core may have cooled more significantly than previously thought.
He and his team concluded that since the Earth’s formation (4.5 billion years ago), the core may have cooled by as much as 1,000 °C (1,832 °F). These findings were rather surprising to the Earth sciences community – leading to what one scientists referred to as the “New Core Heat Paradox“. In short, this rate of core cooling would mean that some other source of energy would be required to sustain the Earth’s geomagnetic field.
On top of this, and related to the issue of core-cooling, were some unresolved questions about the chemical composition of the core. As Dr. Kei Hirose said in a Tokyo Tech press release:
“The core is mostly iron and some nickel, but also contains about 10% of light alloys such as silicon, oxygen, sulfur, carbon, hydrogen, and other compounds. We think that many alloys are simultaneously present, but we don’t know the proportion of each candidate element.”
The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. Credit: ESA/ATG medialab
In order to resolve this, Hirose and his colleagues at ELSI conducted a series of experiments where various alloys were subjected to heat and pressure conditions similar to that in the Earth’s interior. This consisted of using a diamond anvil to squeeze dust-sized alloy samples to simulate high pressure conditions, and then heating them with a laser beam until they reached extreme temperatures.
In the past, research into iron alloys in the core have focused predominantly on either iron-silicon alloys or iron-oxide at high pressures. But for the sake of their experiments, Hirose and his colleagues decided to focus on the combination of silicon and oxygen – which are believed to exist in the outer core – and examining the results with an electron microscope.
What the researchers found was that under conditions of extreme pressure and heat, samples of silicon and oxygen combined to form silicon dioxide crystals – which were similar in composition to mineral quartz found in the Earth’s crust. Ergo, the study showed that the crystallization of silicon dioxide in the outer core would have released enough buoyancy to power core convection and a dynamo effect from as early on as the Hadean eon onward.
As John Hernlund, also a member of ELSI and a co-author of the study, explained:
“This result proved important for understanding the energetics and evolution of the core. We were excited because our calculations showed that crystallization of silicon dioxide crystals from the core could provide an immense new energy source for powering the Earth’s magnetic field.”
Cross-section of Mars revealing its inner core. Mars must have one day had such a field, but the energy source that powered it has since shut down. Credit: NASA/JPL/GSFC
This study not only provides evidence to help resolve the so-called “New Core Heat Paradox”, it also may help advance our understanding of what conditions were like during the formation of Earth and the early Solar System. Basically, if silicon and oxygen form crystal of silicon dioxide in the outer core over time, then sooner or later, the process will stop once the core runs out of these elements.
When that happens, we can expect Earth’s magnetic field will suffer, which will have drastic implications for life on Earth. It also helps to put constraints on the concentrations of silicon and oxygen that were present in the core when the Earth first formed, which could go a long way towards informing our theories about Solar System formation.
What’s more, this research may help geophysicists to determine how and when other planets (like Mars, Venus and Mercury) still had magnetic fields (and possibly lead to ideas of how they could be powered up again). It could even help exoplanet-hunting science teams determine which exoplanets have magnetospheres, which would allow us to find out which extra-solar worlds could be habitable.
To accomplish its science objectives, NASA’s Juno spacecraftorbits over Jupiter’s poles and passes repeatedly through hazardous radiation belts. Two Boston University researchers propose using Juno to probe the ever-changing flux of volcanic gases-turned-ions spewed by Io’s volcanoes. Credit: NASA/JPL-Caltech
Jupiter may be the largest planet in the Solar System with a diameter 11 times that of Earth, but it pales in comparison to its own magnetosphere. The planet’s magnetic domain extends sunward at least 3 million miles (5 million km) and on the back side all the way to Saturn for a total of 407 million miles or more than 400 times the size of the Sun.
Jupiter’s large magnetic field interacts with the solar wind to form an invisible magnetosphere. If we were able to see it, it would span at least several degrees of sky. It would show its greatest extent when viewing Jupiter from the side at quadrature, when the planet stands due south at sunrise or sunset.In the artist’s depiction, the planet would be located between the two “purple eyes” — too small to see at this scale. Credit: NASA.
If we had eyes adapted to see the Jovian magnetosphere at night, its teardrop-like shape would easily extend across several degrees of sky! No surprise then that Jove’s magnetic aura has been called one of the largest structures in the Solar System.
A 5-frame sequence taken by the New Horizons spacecraft in May 2007 shows a cloud of volcanic debris from Io’s Tvashtar volcano. The plume extends some 200 miles (330 km) above the moon’s surface. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Io, Jupiter’s innermost of the planet’s four large moons, orbits deep within this giant bubble. Despite its small size — about 200 miles smaller than our own Moon — it doesn’t lack in superlatives. With an estimated 400 volcanoes, many of them still active, Io is the most volcanically active body in the Solar System. In the moon’s low gravity, volcanoes spew sulfur, sulfur dioxide gas and fragments of basaltic rock up to 310 miles (500 km) into space in beautiful, umbrella-shaped plumes.
This schematic of Jupiter’s magnetic environments shows the planets looping magnetic field lines (similar to those generated by a simple bar magnet), Io and its plasma torus and flux tube. Credit: John Spencer / Wikipedia CC-BY-SA3.0 with labels by the author
Once aloft, electrons whipped around by Jupiter’s powerful magnetic field strike the neutral gases and ionize them (strips off their electrons). Ionized atoms and molecules (ions) are no longer neutral but possess a positive or negative electric charge. Astronomers refer to swarms of ionized atoms as plasma.
Jupiter rotates rapidly, spinning once every 9.8 hours, dragging the whole magnetosphere with it. As it spins past Io, those volcanic ions get caught up and dragged along for the ride, rotating around the planet in a ring called the Io plasma torus. You can picture it as a giant donut with Jupiter in the “hole” and the tasty, ~8,000-mile-thick ring centered on Io’s orbit.
That’s not all. Jupiter’s magnetic field also couples Io’s atmosphere to the planet’s polar regions, pumping Ionian ions through two “pipelines” to the magnetic poles and generating a powerful electric current known as the Io flux tube. Like firefighters on fire poles, the ions follow the planet’s magnetic field lines into the upper atmosphere, where they strike and excite atoms, spawning an ultraviolet-bright patch of aurora within the planet’s overall aurora. Astronomers call it Io’s magnetic footprint. The process works in reverse, too, spawning auroras in Io’s tenuous atmosphere.
The tilt of Juno’s orbit relative to Jupiter changes over the course of the mission, sending the spacecraft increasingly deeper into the planet’s intense radiation belts. Orbits are numbered from early in the mission to late. Credit: NASA/JPL-Caltech
Io is the main supplier of particles to Jupiter’s magnetosphere. Some of the same electrons stripped from sulfur and oxygen atoms during an earlier eruption return to strike atoms shot out by later blasts. Round and round they go in a great cycle of microscopic bombardment! The constant flow of high-speed, charged particles in Io’s vicinity make the region a lethal environment not only for humans but also for spacecraft electronics, the reason NASA’s Juno probe gets the heck outta there after each perijove or closest approach to Jupiter.
Io’s flux tube directs ions down Jupiter’s magnetic field lines to create magnetic footprints of enhanced aurora in Jupiter’s polar regions. An electric current of 5 million amps flows along Io’s flux tube.Credit: NASA/J.Clarke/HST
But there’s much to glean from those plasma streams. Astronomy PhD student Phillip Phipps and assistant professor of astronomy Paul Withers of Boston University have hatched a plan to use the Juno spacecraft to probe Io’s plasma torus to indirectly study the timing and flow of material from Io’s volcanoes into Jupiter’s magnetosphere. In a paper published on Jan. 25, they propose using changes in the radio signal sent by Juno as it passes through different regions of the torus to measure how much stuff is there and how its density changes over time.
The technique is called a radio occultation. Radio waves are a form of light just like white light. And like white light, they get bent or refracted when passing through a medium like air (or plasma in the case of Io). Blue light is slowed more and experiences the most bending; red light is slowed less and refracted least, the reason red fringes a rainbow’s outer edge and blue its inner. In radio occultations, refraction results in changes in frequency caused by variations in the density of plasma in Io’s torus.
The best spacecraft for the attempt is one with a polar orbit around Jupiter, where it cuts a clean cross-section through different parts of the torus during each orbit. Guess what? With its polar orbit, Juno’s the probe for the job! Its main mission is to map Jupiter’s gravitational and magnetic fields, so an occultation experiment jives well with mission goals. Previous missions have netted just two radio occultations of the torus, but Juno could potentially slam dunk 24.
New Horizons took this photo of Io in infrared light. The Tvastar volcano is bright spot at top. At least 10 other volcanic hot spots dot the moon’s night side. Credit: NASA/JHUPL/SRI
Because the paper was intended to show that the method is a feasible one, it remains to be seen whether NASA will consider adding a little extra credit work to Juno’s homework. It seems a worthy and practical goal, one that will further enlighten our understanding of how volcanoes create aurorae in the bizarre electric and magnetic environment of the largest planet.
Science fiction has told us again and again, we belong out there, among the stars. But before we can build that vast galactic empire, we’ve got to learn how to just survive in space. Fortunately, we happen to live in a Solar System with many worlds, large and small that we can use to become a spacefaring civilization.
This is half of an epic two-part article that I’m doing with Isaac Arthur, who runs an amazing YouTube channel all about futurism, often about the exploration and colonization of space. Make sure you subscribe to his channel.
This article is about colonizing the inner Solar System, from tiny Mercury, the smallest planet, out to Mars, the focus of so much attention by Elon Musk and SpaceX. In the other article, Isaac will talk about what it’ll take to colonize the outer Solar System, and harness its icy riches. You can read these articles in either order, just read them both.
At the time I’m writing this, humanity’s colonization efforts of the Solar System are purely on Earth. We’ve exploited every part of the planet, from the South Pole to the North, from huge continents to the smallest islands. There are few places we haven’t fully colonized yet, and we’ll get to that.
But when it comes to space, we’ve only taken the shortest, most tentative steps. There have been a few temporarily inhabited space stations, like Mir, Skylab and the Chinese Tiangong Stations.
Our first and only true colonization of space is the International Space Station, built in collaboration with NASA, ESA, the Russian Space Agency and other countries. It has been permanently inhabited since November 2nd, 2000. Needless to say, we’ve got our work cut out for us.
NASA astronaut Tracy Caldwell Dyson, an Expedition 24 flight engineer in 2010, took a moment during her space station mission to enjoy an unmatched view of home through a window in the Cupola of the International Space Station, the brilliant blue and white part of Earth glowing against the blackness of space. Credits: NASA
Before we talk about the places and ways humans could colonize the rest of the Solar System, it’s important to talk about what it takes to get from place to place.
Just to get from the surface of Earth into orbit around our planet, you need to be going about 10 km/s sideways. This is orbit, and the only way we can do it today is with rockets. Once you’ve gotten into Low Earth Orbit, or LEO, you can use more propellant to get to other worlds.
If you want to travel to Mars, you’ll need an additional 3.6 km/s in velocity to escape Earth gravity and travel to the Red Planet. If you want to go to Mercury, you’ll need another 5.5 km/s.
And if you wanted to escape the Solar System entirely, you’d need another 8.8 km/s. We’re always going to want a bigger rocket.
The most efficient way to transfer from world to world is via the Hohmann Transfer. This is where you raise your orbit and drift out until you cross paths with your destination. Then you need to slow down, somehow, to go into orbit.
One of our primary goals of exploring and colonizing the Solar System will be to gather together the resources that will make future colonization and travel easier. We need water for drinking, and to split it apart for oxygen to breathe. We can also turn this water into rocket fuel. Unfortunately, in the inner Solar System, water is a tough resource to get and will be highly valued.
We need solid ground. To build our bases, to mine our resources, to grow our food, and to protect us from the dangers of space radiation. The more gravity we can get the better, since low gravity softens our bones, weakens our muscles, and harms us in ways we don’t fully understand.
Each world and place we colonize will have advantages and disadvantages. Let’s be honest, Earth is the best place in the Solar System, it’s got everything we could ever want and need. Everywhere else is going to be brutally difficult to colonize and make self-sustaining.
We do have one huge advantage, though. Earth is still here, we can return whenever we like. The discoveries made on our home planet will continue to be useful to humanity in space through communications, and even 3D printing. Once manufacturing is sophisticated enough, a discovery made on one world could be mass produced half a solar system away with the right raw ingredients.
We will learn how to make what we need, wherever we are, and how to transport it from place to place, just like we’ve always done.
Mercury, as imaged by the MESSENGER spacecraft, revealing parts of the never seen by human eyes. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Mercury is the closest planet from the Sun, and one of the most difficult places that we might attempt the colonize. Because it’s so close to the Sun, it receives an enormous amount of energy. During the day, temperatures can reach 427 C, but without an atmosphere to trap the heat, night time temperatures dip down to -173 C. There’s essentially no atmosphere, 38% the gravity of Earth, and a single solar day on Mercury lasts 176 Earth days.
Mercury does have some advantages, though. It has an average density almost as high as Earth, but because of its smaller size, it actually means it has a higher percentage of metal than Earth. Mercury will be incredibly rich in metals and minerals that future colonists will need across the Solar System.
With the lower gravity and no atmosphere, it’ll be far easier to get that material up into orbit and into transfer trajectories to other worlds.
But with the punishing conditions on the planet, how can we live there? Although the surface of Mercury is either scorching or freezing, NASA’s MESSENGER spacecraft turned up regions of the planet which are in eternal shadow near the poles. In fact, these areas seem to have water ice, which is amazing for anywhere this close to the Sun.
Images of Mercury’s northern polar region, provided by MESSENGER. Credit: NASA/JPL
You could imagine future habitats huddled into those craters, pulling in solar power from just over the crater rim, using the reservoirs of water ice for air, fuel and water.
High powered solar robots could scour the surface of Mercury, gathering rare metals and other minerals to be sent off world. Because it’s bathed in the solar winds, Mercury will have large deposits of Helium-3, useful for future fusion reactors.
Over time, more and more of the raw materials of Mercury will find their way to the resource hungry colonies spread across the Solar System.
It also appears there are lava tubes scattered across Mercury, hollows carved out by lava flows millions of years ago. With work, these could be turned into safe, underground habitats, protected from the radiation, high temperatures and hard vacuum on the surface.
With enough engineering ability, future colonists will be able to create habitats on the surface, wherever they like, using a mushroom-shaped heat shield to protect a colony built on stilts to keep it off the sun-baked surface.
Mercury is smaller than Mars, but is a good deal denser, so it has about the same gravity, 38% of Earth’s. Now that might turn out to be just fine, but if we need more, we have the option of using centrifugal force to increase it. Space Stations can generate artificial gravity by spinning, but you can combine normal gravity with spin-gravity to create a stronger field than either would have.
So our mushroom habitat’s stalk could have an interior spinning section with higher gravity for those living inside it. You get a big mirror over it, shielding you from solar radiation and heat, you have stilts holding it off the ground, like roots, that minimize heat transfer from the warmer areas of ground outside the shield, and if you need it you have got a spinning section inside the stalk. A mushroom habitat.
Venus as photographed by the Pioneer spacecraft in 1978. Credit: NASA/JPL/Caltech
Venus is the second planet in the Solar System, and it’s the evil twin of Earth. Even though it has roughly the same size, mass and surface gravity of our planet, it’s way too close to the Sun. The thick atmosphere acts like a blanket, trapping the intense heat, pushing temperatures at the surface to 462 C.
Everywhere on the planet is 462 C, so there’s no place to go that’s cooler. The pure carbon dioxide atmosphere is 90 times thicker than Earth, which is equivalent to being a kilometer beneath the ocean on Earth.
In the beginning, colonizing the surface of Venus defies our ability. How do you survive and stay cool in a thick poisonous atmosphere, hot enough to melt lead? You get above it.
One of the most amazing qualities of Venus is that if you get into the high atmosphere, about 52.5 kilometers up, the air pressure and temperature are similar to Earth. Assuming you can get above the poisonous clouds of sulphuric acid, you could walk outside a floating colony in regular clothes, without a pressure suit. You’d need a source of breathable air, though.
Even better, breathable air is a lifting gas in the cloud tops of Venus. You could imagine a future colony, filled with breathable air, floating around Venus. Because the gravity on Venus is roughly the same as Earth, humans wouldn’t suffer any of the side effects of microgravity. In fact, it might be the only place in the entire Solar System other than Earth where we don’t need to account for low gravity.
Artist’s concept of a Venus cloud city — a possible future outcome of the High Altitude Venus Operational Concept (HAVOC) plan. Credit: Advanced Concepts Lab at NASA Langley Research Center
Now the day on Venus is incredibly long, 243 earth days, so if you stay over the same place the whole time it would be light for four months then dark for four months. Not ideal for solar power on a first glance, but Venus turns so slowly that even at the equator you could stay ahead of the sunset at a fast walk.
So if you have floating colonies it would take very little effort to stay constantly on the light side or dark side or near the twilight zone of the terminator. You are essentially living inside a blimp, so it may as well be mobile. And on the day side it would only take a few solar panels and some propellers to stay ahead. And since it is so close to the Sun, there’s plenty of solar power. What could you do with it?
The atmosphere itself would probably serve as a source of raw materials. Carbon is the basis for all life on Earth. We’ll need it for food and building materials in space. Floating factories could process the thick atmosphere of Venus, to extract carbon, oxygen, and other elements.
Heat resistant robots could be lowered down to the surface to gather minerals and then retrieved before they’re cooked to death.
Venus does have a high gravity, so launching rockets up into space back out of Venus’ gravity well will be expensive.
Over longer periods of time, future colonists might construct large solar shades to shield themselves from the scorching heat, and eventually, even start cooling the planet itself.
Earth as seen on July 6, 2015 from a distance of one million miles by a NASA scientific camera aboard the Deep Space Climate Observatory spacecraft. Credits: NASA
The next planet from the Sun is Earth, the best planet in the Solar System. One of the biggest advantages of our colonization efforts will be to get heavy industry off our planet and into space. Why pollute our atmosphere and rivers when there’s so much more space… in space.
Over time, more and more of the resource gathering will happen off world, with orbital power generation, asteroid mining, and zero gravity manufacturing. Earth’s huge gravity well means that it’s best to bring materials down to Earth, not carry them up to space.
However, the normal gravity, atmosphere and established industry of Earth will allow us to manufacture the lighter high tech goods that the rest of the Solar System will need for their own colonization efforts.
But we haven’t completely colonized Earth itself. Although we’ve spread across the land, we know very little about the deep ocean. Future colonies under the oceans will help us learn more about self-sufficient colonies, in extreme environments. The oceans on Earth will be similar to the oceans on Europa or Enceladus, and the lessons we learn here will teach us to live out there.
As we return to space, we’ll colonize the region around our planet. We’ll construct bigger orbital colonies in Low Earth Orbit, building on our lessons from the International Space Station.
One of the biggest steps we need to take, is understanding how to overcome the debilitating effects of microgravity: the softened bones, weakened muscles and more. We need to perfect techniques for generating artificial gravity where there is none.
A 1969 station concept. The station was to rotate on its central axis to produce artificial gravity. The majority of early space station concepts created artificial gravity one way or another in order to simulate a more natural or familiar environment for the health of the astronauts. Credit: NASA
The best technique we have is rotating spacecraft to generate artificial gravity. Just like we saw in 2001, and The Martian, by rotating all or a portion of a spacecraft, you can generated an outward centrifugal force that mimics the acceleration of gravity. The larger the radius of the space station, the more comfortable and natural the rotation feels.
Low Earth Orbit also keeps a space station within the Earth’s protective magnetosphere, limiting the amount of harmful radiation that future space colonists will experience.
Other orbits are useful too, including geostationary orbit, which is about 36,000 kilometers above the surface of the Earth. Here spacecraft orbit the Earth at exactly the same rate as the rotation of Earth, which means that stations appear in fixed positions above our planet, useful for communication.
Geostationary orbit is higher up in Earth’s gravity well, which means these stations will serve a low-velocity jumping off points to reach other places in the Solar System. They’re also outside the Earth’s atmospheric drag, and don’t require any orbital boosting to keep them in place.
By perfecting orbital colonies around Earth, we’ll develop technologies for surviving in deep space, anywhere in the Solar System. The same general technology will work anywhere, whether we’re in orbit around the Moon, or out past Pluto.
When the technology is advanced enough, we might learn to build space elevators to carry material and up down from Earth’s gravity well. We could also build launch loops, electromagnetic railguns that launch material into space. These launch systems would also be able to loft supplies into transfer trajectories from world to world throughout the Solar System.
Earth orbit, close to the homeworld gives us the perfect place to develop and perfect the technologies we need to become a true spacefaring civilization. Not only that, but we’ve got the Moon.
Sample collection on the surface of the Moon. Apollo 16 astronaut Charles M. Duke Jr. is shown collecting samples with the Lunar Roving Vehicle in the left background. Image: NASA
The Moon, of course, is the Earth’s only natural satellite, which orbits us at an average distance of about 400,000 kilometers. Almost ten times further than geostationary orbit.
The Moon takes a surprising amount of velocity to reach from Low Earth Orbit. It’s close, but expensive to reach, thrust speaking.
But that fact that it’s close makes the Moon an ideal place to colonize. It’s close to Earth, but it’s not Earth. It’s airless, bathed in harmful radiation and has very low gravity. It’s the place that humanity will learn to survive in the harsh environment of space.
But it still does have some resources we can exploit. The lunar regolith, the pulverized rocky surface of the Moon, can be used as concrete to make structures. Spacecraft have identified large deposits of water at the Moon’s poles, in its permanently shadowed craters. As with Mercury, these would make ideal locations for colonies.
Here, a surface exploration crew begins its investigation of a typical, small lava tunnel, to determine if it could serve as a natural shelter for the habitation modules of a Lunar Base. Credit: NASA’s Johnson Space Center
Our spacecraft have also captured images of openings to underground lava tubes on the surface of the Moon. Some of these could be gigantic, even kilometers high. You could fit massive cities inside some of these lava tubes, with room to spare.
Helium-3 from the Sun rains down on the surface of the Moon, deposited by the Sun’s solar wind, which could be mined from the surface and provide a source of fuel for lunar fusion reactors. This abundance of helium could be exported to other places in the Solar System.
The far side of the Moon is permanently shadowed from Earth-based radio signals, and would make an ideal location for a giant radio observatory. Telescopes of massive size could be built in the much lower lunar gravity.
We talked briefly about an Earth-based space elevator, but an elevator on the Moon makes even more sense. With the lower gravity, you can lift material off the surface and into lunar orbit using cables made of materials we can manufacture today, such as Zylon or Kevlar.
One of the greatest threats on the Moon is the dusty regolith itself. Without any kind of weathering on the surface, these dust particles are razor sharp, and they get into everything. Lunar colonists will need very strict protocols to keep the lunar dust out of their machinery, and especially out of their lungs and eyes, otherwise it could cause permanent damage.
Artist’s impression of a Near-Earth Asteroid passing by Earth. Credit: ESA
Although the vast majority of asteroids in the Solar System are located in the main asteroid belt, there are still many asteroids orbiting closer to Earth. These are known as the Near Earth Asteroids, and they’ve been the cause of many of Earth’s great extinction events.
These asteroids are dangerous to our planet, but they’re also an incredible resource, located close to our homeworld.
The amount of velocity it takes to get to some of these asteroids is very low, which means travel to and from these asteroids takes little energy. Their low gravity means that extracting resources from their surface won’t take a tremendous amount of energy.
And once the orbits of these asteroids are fully understood, future colonists will be able to change the orbits using thrusters. In fact, the same system they use to launch minerals off the surface would also push the asteroids into safer orbits.
These asteroids could be hollowed out, and set rotating to provide artificial gravity. Then they could be slowly moved into safe, useful orbits, to act as space stations, resupply points, and permanent colonies.
There are also gravitationally stable points at the Sun-Earth L4 and L5 Lagrange Points. These asteroid colonies could be parked there, giving us more locations to live in the Solar System.
Mosaic of the Valles Marineris hemisphere of Mars, similar to what one would see from orbital distance of 2500 km. Credit: NASA/JPL-Caltech
The future of humanity will include the colonization of Mars, the fourth planet from the Sun. On the surface, Mars has a lot going for it. A day on Mars is only a little longer than a day on Earth. It receives sunlight, unfiltered through the thin Martian atmosphere. There are deposits of water ice at the poles, and under the surface across the planet.
Martian ice will be precious, harvested from the planet and used for breathable air, rocket fuel and water for the colonists to drink and grow their food. The Martian regolith can be used to grow food. It does have have toxic perchlorates in it, but that can just be washed out.
The lower gravity on Mars makes it another ideal place for a space elevator, ferrying goods up and down from the surface of the planet.
The area depicted is Noctis Labyrinthus in the Valles Marineris system of enormous canyons. The scene is just after sunrise, and on the canyon floor four miles below, early morning clouds can be seen. The frost on the surface will melt very quickly as the Sun climbs higher in the Martian sky. Credit: NASA
Unlike the Moon, Mars has a weathered surface. Although the planet’s red dust will get everywhere, it won’t be toxic and dangerous as it is on the Moon.
Like the Moon, Mars has lava tubes, and these could be used as pre-dug colony sites, where human Martians can live underground, protected from the hostile environment.
Mars has two big problems that must be overcome. First, the gravity on Mars is only a third that of Earth’s, and we don’t know the long term impact of this on the human body. It might be that humans just can’t mature properly in the womb in low gravity.
Researchers have proposed that Mars colonists might need to spend large parts of their day on rotating centrifuges, to simulate Earth gravity. Or maybe humans will only be allowed to spend a few years on the surface of Mars before they have to return to a high gravity environment.
The second big challenge is the radiation from the Sun and interstellar cosmic rays. Without a protective magnetosphere, Martian colonists will be vulnerable to a much higher dose of radiation. But then, this is the same challenge that colonists will face anywhere in the entire Solar System.
That radiation will cause an increased risk of cancer, and could cause mental health issues, with dementia-like symptoms. The best solution for dealing with radiation is to block it with rock, soil or water. And Martian colonists, like all Solar System colonists will need to spend much of their lives underground or in tunnels carved out of rock.
Two astronauts explore the rugged surface of Phobos. Mars, as it would appear to the human eye from Phobos, looms on the horizon. The mother ship, powered by solar energy, orbits Mars while two crew members inside remotely operate rovers on the Martian surface. Credit: NASA/Pat Rawlings (SAIC)
In addition to Mars itself, the Red Planet has two small moons, Phobos and Deimos. These will serve as ideal places for small colonies. They’ll have the same low gravity as asteroid colonies, but they’ll be just above the gravity well of Mars. Ferries will travel to and from the Martian moons, delivering fresh supplies and sending Martian goods out to the rest of the Solar System.
We’re not certain yet, but there are good indicators these moons might have ice inside them, if so that is an excellent source of fuel and could make initial trips to Mars much easier by allowing us to send a first expedition to those moons, who then begin producing fuel to be used to land on Mars and to leave Mars and return home.
According to Elon Musk, if a Martian colony can reach a million inhabitants, it’ll be self-sufficient from Earth or any other world. At that point, we would have a true, Solar System civilization.
Now, continue on to the other half of this article, written by Isaac Arthur, where he talks about what it will take to colonize the outer Solar System. Where water ice is plentiful but solar power is feeble. Where travel times and energy require new technologies and techniques to survive and thrive.
The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. Credit: ESA/ATG medialab
Everyone knows just how fun magnets can be. As a child, who among us didn’t love to see if we could make our silverware stick together? And how about those little magnetic rocks that we could arrange to form just about any shape because they stuck together? Well, magnetism is not just an endless source of fun or good for scientific experiments; it’s also one of basic physical laws upon which the universe is based.
The attraction known as magnetism occurs when a magnetic field is present, which is a field of force produced by a magnetic object or particle. It can also be produced by a changing electric field and is detected by the force it exerts on other magnetic materials. Hence why the area of study dealing with magnets is known as electromagnetism.
Definition:
Magnetic fields can be defined in a number of ways, depending on the context. However, in general terms, it is an invisible field that exerts magnetic force on substances which are sensitive to magnetism. Magnets also exert forces and torques on each other through the magnetic fields they create.
Visualization of the solar wind encountering Earth’s magnetosphere. Like a dipole magnet, it has field lines and a northern and southern pole. Credit: JPL
They can be generated within the vicinity of a magnet, by an electric current, or a changing electrical field. They are dipolar in nature, which means that they have both a north and south magnetic pole. The Standard International (SI) unit used to measure magnetic fields is the Tesla, while smaller magnetic fields are measured in terms of Gauss (1 Tesla = 10,000 Guass).
Mathematically, a magnetic field is defined in terms of the amount of force it exerted on a moving charge. The measurement of this force is consistent with the Lorentz Force Law, which can be expressed as F= qvB, where F is the magnetic force, q is the charge, v is the velocity, and the magnetic field is B. This relationship is a vector product, where F is perpendicular (->) to all other values.
Field Lines:
Magnetic fields may be represented by continuous lines of force (or magnetic flux) that emerge from north-seeking magnetic poles and enter south-seeking poles. The density of the lines indicate the magnitude of the field, being more concentrated at the poles (where the field is strong) and fanning out and weakening the farther they get from the poles.
A uniform magnetic field is represented by equally-spaced, parallel straight lines. These lines are continuous, forming closed loops that run from north to south, and looping around again. The direction of the magnetic field at any point is parallel to the direction of nearby field lines, and the local density of field lines can be made proportional to its strength.
Magnetic field lines resemble a fluid flow, in that they are streamlined and continuous, and more (or fewer lines) appear depending on how closely a field is observed. Field lines are useful as a representation of magnetic fields, allowing for many laws of magnetism (and electromagnetism) to be simplified and expressed in mathematical terms.
A simple way to observe a magnetic field is to place iron filings around an iron magnet. The arrangements of these filings will then correspond to the field lines, forming streaks that connect at the poles. They also appear during polar auroras, in which visible streaks of light line up with the local direction of the Earth’s magnetic field.
History of Study:
The study of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field of a spherical magnet using iron needles. The places where these lines crossed he named “poles” (in reference to Earth’s poles), which he would go on to claim that all magnets possessed.
During the 16th century, English physicist and natural philosopher William Gilbert of Colchester replicated Peregrinus’ experiment. In 1600, he published his findings in a treaties (De Magnete) in which he stated that the Earth is a magnet. His work was intrinsic to establishing magnetism as a science.
View of the eastern sky during the peak of this morning’s aurora. Credit: Bob King
In 1750, English clergyman and philosopher John Michell stated that magnetic poles attract and repel each other. The force with which they do this, he observed, is inversely proportional to the square of the distance, otherwise known as the inverse square law.
In 1785, French physicist Charles-Augustin de Coulomb experimentally verified Earths’ magnetic field. This was followed by 19th century French mathematician and geometer Simeon Denis Poisson created the first model of the magnetic field, which he presented in 1824.
By the 19th century, further revelations refined and challenged previously-held notions. For example, in 1819, Danish physicist and chemist Hans Christian Orsted discovered that an electric current creates a magnetic field around it. In 1825, André-Marie Ampère proposed a model of magnetism where this force was due to perpetually flowing loops of current, instead of the dipoles of magnetic charge.
In 1831, English scientist Michael Faraday showed that a changing magnetic field generates an encircling electric field. In effect, he discovered electromagnetic induction, which was characterized by Faraday’s law of induction (aka. Faraday’s Law).
A Faraday cage in power plant in Heimbach, Germany. Credit: Wikipedia Commons/Frank Vincentz
Between 1861 and 1865, Scottish scientist James Clerk Maxwell published his theories on electricity and magnetism – known as the Maxwell’s Equations. These equations not only pointed to the interrelationship between electricity and magnetism, but showed how light itself is an electromagnetic wave.
The field of electrodynamics was extended further during the late 19th and 20th centuries. For instance, Albert Einstein (who proposed the Law of Special Relativity in 1905), showed that electric and magnetic fields are part of the same phenomena viewed from different reference frames. The emergence of quantum mechanics also led to the development of quantum electrodynamics (QED).
Examples:
A classic example of a magnetic field is the field created by an iron magnet. As previously mentioned, the magnetic field can be illustrated by surrounding it with iron filings, which will be attracted to its field lines and form in a looping formation around the poles.
Larger examples of magnetic fields include the Earth’s magnetic field, which resembles the field produced by a simple bar magnet. This field is believed to be the result of movement in the Earth’s core, which is divided between a solid inner core and molten outer core which rotates in the opposite direction of Earth. This creates a dynamo effect, which is believed to power Earth’s magnetic field (aka. magnetosphere).
Computer simulation of the Earth’s field in a period of normal polarity between reversals.[1] The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. Credit: NASASuch a field is called a dipole field because it has two poles – north and south, located at either end of the magnet – where the strength of the field is at its maximum. At the midpoint between the poles the strength is half of its polar value, and extends tens of thousands of kilometers into space, forming the Earth’s magnetosphere.
Other celestial bodies have been shown to have magnetic fields of their own. This includes the gas and ice giants of the Solar System – Jupiter, Saturn, Uranus and Neptune. Jupiter’s magnetic field is 14 times as powerful as that of Earth, making it the strongest magnetic field of any planetary body. Jupiter’s moon Ganymede also has a magnetic field, and is the only moon in the Solar System known to have one.
Mars is believed to have once had a magnetic field similar to Earth’s, which was also the result of a dynamo effect in its interior. However, due to either a massive collision, or rapid cooling in its interior, Mars lost its magnetic field billions of years ago. It is because of this that Mars is believed to have lost most of its atmosphere, and the ability to maintain liquid water on its surface.
When it comes down to it, electromagnetism is a fundamental part of our Universe, right up there with nuclear forces and gravity. Understanding how it works, and where magnetic fields occur, is not only key to understanding how the Universe came to be, but may also help us to find life beyond Earth someday.
Aurora borealis in Fairbanks, AK. on Monday night March 16. Credit: John Chumack
The Northern Lights have fascinated human beings for millennia. In fact, their existence has informed the mythology of many cultures, including the Inuit, Northern Cree, and ancient Norse. They were also a source of intense fascination for the ancient Greeks and Romans, and were seen as a sign from God by medieval Europeans.
Thanks to the birth of modern astronomy, we now know what causes both the Aurora Borealis and its southern sibling – Aurora Australis. Nevertheless, they remain the subject of intense fascination, scientific research, and are a major tourist draw. For those who live north of 60° latitude, this fantastic light show is also a regular occurrence.
Causes:
Aurora Borealis (and Australis) is caused by interactions between energetic particles from the Sun and the Earth’s magnetic field. The invisible field lines of Earth’s magnetoshere travel from the Earth’s northern magnetic pole to its southern magnetic pole. When charged particles reach the magnetic field, they are deflected, creating a “bow shock” (so-named because of its apparent shape) around Earth.
However, Earth’s magnetic field is weaker at the poles, and some particles are therefore able to enter the Earth’s atmosphere and collide with gas particles in these regions. These collisions emit light that we perceive as wavy and dancing, and are generally a pale, yellowish-green in color.
The variations in color are due to the type of gas particles that are colliding. The common yellowish-green is produced by oxygen molecules located about 100 km (60 miles) above the Earth, whereas high-altitude oxygen – at heights of up to 320 km (200 miles) – produce all-red auroras. Meanwhile, interactions between charged particles and nitrogen will produces blue or purplish-red auroras.
Variability:
The visibility of the northern (and southern) lights depends on a lot of factors, much like any other type of meteorological activity. Though they are generally visible in the far northern and southern regions of the globe, there have been instances in the past where the lights were visible as close to the equator as Mexico.
In places like Alaska, Norther Canada, Norway and Siberia, the northern lights are often seen every night of the week in the winter. Though they occur year-round, they are only visible when it is rather dark out. Hence why they are more discernible during the months where the nights are longer.
The magnetic field and electric currents in and around Earth generate complex forces, and also lead to the phenomena known as aurorae. Credit: ESA/ATG medialab
Because they depend on the solar wind, auroras are more plentiful during peak periods of activity in the Solar Cycle. This cycle takes places every 11 years, and is marked by the increase and decrease of sunspots on the sun’s surface. The greatest number of sunspots in any given solar cycle is designated as a “Solar Maximum“, whereas the lowest number is a “Solar Minimum.”
A Solar Maximum also accords with bright regions appearing in the Sun’s corona, which are rooted in the lower sunspots. Scientists track these active regions since they are often the origin of eruptions on the Sun, such as solar flares or coronal mass ejections.
The most recent solar minimum occurred in 2008. As of January 2010, the Sun’s surface began to increase in activity, which began with the release of a lower-intensity M-class flare. The Sun continued to get more active, culminating in a Solar Maximum by the summer of 2013.
Locations for Viewing:
The ideal places to view the Northern Lights are naturally located in geographical regions north of 60° latitude. These include northern Canada, Greenland, Iceland, Scandinavia, Alaska, and Northern Russia. Many organizations maintain websites dedicated to tracking optimal viewing conditions.
An image captured of the northern lights, which appear pale purple and red, though the primary color visible to the eye was green. Credit: Bob Kin
For instance, the Geophysical Institute of the University of Alaska Fairbanks maintains the Aurora Forecast. This site is regularly updated to let residents know when auroral activity is high, and how far south it will extend. Typically, residents who live in central or northern Alaska (from Fairbanks to Barrow) have a better chance than those living in the south (Anchorage to Juneau).
In Northern Canada, auroras are often spotted from the Yukon, the Northwest Territories, Nunavut, and Northern Quebec. However, they are sometimes seen from locations like Dawson Creek, BC; Fort McMurry, Alberta; northern Saskatchewan and the town of Moose Factory by James Bay, Ontario. For information, check out Canadian Geographic Magazine’s “Northern Lights Across Canada“.
The National Oceanic and Atmospheric Agency also provides 30 minute forecasts on auroras through their Space Weather Prediction Center. And then there’s Aurora Alert, an Android App that allows you to get regular updates on when and where an aurora will be visible in your region.
Understanding the scientific cause of auroras has not made them any less awe-inspiring or wondrous. Every year, countless people venture to locations where they can be seen. And for those serving aboard the ISS, they got the best seat in the house!
Speaking of which, be sure to check out this stunning NASA video which shows the Northern Lights being viewed from the ISS:
For more information, visit the THEMIS website – a NASA mission that is currently studying space weather in great detail. The Space Weather Center has information on the solar wind and how it causes aurorae.
Earth’s atmosphere seen from space. The top layer of the stratosphere is the ozone layer, which protects us from harmful solar UV. Scientists are tracking the ozone hole over the Antarctic. Credit: NASA
We here at Earth are fortunate that we have a viable atmosphere, one that is protected by Earth’s magnetosphere. Without this protective envelope, life on the surface would be bombarded by harmful radiation emanating from the Sun. However, Earth’s upper atmosphere is still slowly leaking, with about 90 tonnes of material a day escaping from the upper atmosphere and streaming into space.
And although astronomers have been investigating this leakage for some time, there are still many unanswered questions. For example, how much material is being lost to space, what kinds, and how does this interact with solar wind to influence our magnetic environment? Such has been the purpose of the European Space Agency’s Cluster project, a series of four identical spacecraft that have been measuring Earth’s magnetic environment for the past 15 years.
Understanding our atmosphere’s interaction with solar wind first requires that we understand how Earth’s magnetic field works. For starters, it extends from the interior of our planet (and is believed to be the result of a dynamo effect in the core), and reaches all the way out into space. This region of space, which our magnetic field exerts influence over, is known as the magnetosphere.
The four Cluster spacecraft crossing the northern cusp of Earth’s magnetosphere. Credit: ESA/AOES Medialab
The inner portion of this magnetosphere is called the plasmasphere, a donut-shaped region which extends to a distance of about 20,000 km from the Earth and co-rotates with it. The magnetosphere is also flooded with charged particles and ions that get trapped inside, and then are sent bouncing back and forth along the region’s field lines.
At its forward, Sun-facing edge, the magnetosphere meets the solar wind – a stream of charged particles flowing from the Sun into space. The spot where they make contact is known as the “Bow Shock”, which is so-named because its magnetic field lines force solar wind to take on the shape of a bow as they pass over and around us.
As the solar wind passes over Earth’s magnetosphere, it comes together again behind our planet to form a magnetotail – an elongated tube which contains trapped sheets of plasma and interacting field lines. Without this protective envelope, Earth’s atmosphere would have been slowly stripped away billions of years ago, a fate that is now believed to have befallen Mars.
That being said, Earth’s magnetic field is not exactly hermetically sealed. For example, at our planet’s poles, the field lines are open, which allows solar particles to enter and fill our magnetosphere with energetic particles. This process is what is responsible for Aurora Borealis and Aurora Australis (aka. the Northern and Southern Lights).
An illustration showing the natural barrier Earth gives us against solar radiation. Credit: NASA.
At the same time, particles from Earth’s upper atmosphere (the ionosphere) can escape the same way, traveling up through the poles and being lost to space. Despite learning much about Earth’s magnetic fields and how plasma is formed through its interaction with various particles, much about the whole process has been unclear until quite recently.
As Arnaud Masson, ESA’s Deputy Project Scientist for the Cluster mission stated in an ESA press release:
“The question of plasma transport and atmospheric loss is relevant for both planets and stars, and is an incredibly fascinating and important topic. Understanding how atmospheric matter escapes is crucial to understanding how life can develop on a planet. The interaction between incoming and outgoing material in Earth’s magnetosphere is a hot topic at the moment; where exactly is this stuff coming from? How did it enter our patch of space?“
Given that our atmosphere contains 5 quadrillion tons of matter (that’s 5 x 1015, or 5,000,000 billion tons), a loss of 90 tons a day doesn’t amount to much. However, this number does not include the mass of “cold ions” that are regularly being added. This term is typically used to described the hydrogen ions that we now know are being lost to the magnetosphere on a regular basis (along with oxygen and helium ions).
Since hydrogen requires less energy to escape our atmosphere, the ions that are created once this hydrogen becomes part of the plasmasphere also have low energy. As a result, they have been very difficult to detect in the past. What’s more, scientists have only known about this flow of oxygen, hydrogen and helium ions – which come from the Earth’s polar regions and replenish plasma in the magnetosphere – for a few decades.
Illustration of ions flowing out from the polar cap towards the magnetotail. Credit: ESA – C. Carreau
Prior to this, scientists believed that solar particles alone were responsible for plasma in Earth’s magnetosphere. But in more recent years, they have come to understand that two other sources contribute to the plasmasphere. The first are sporadic “plumes” of plasma that grow within the plasmasphere and travel outwards towards the edge of the magnetosphere, where they interact with solar wind plasma coming the other way.
The other source? The aforementioned atmospheric leakage. Whereas this consists of abundant oxygen, helium and hydrogen ions, the cold hydrogen ions appear to play the most important role. Not only do they constitute a significant amount of matter lost to space, and may play a key role in shaping our magnetic environment. What’s more, most of the satellites currently orbiting Earth are unable to detect the cold ions being added to the mix, something which Cluster is able to do.
In 2009 and in 2013, the Cluster probes were able to characterize their strength, as well as that of other sources of plasma being added to the Earth’s magnetosphere. When only the cold ions are considered, the amount of atmosphere being lost o space amounts to several thousand tons per year. In short, its like losing socks. Not a big deal, but you’d like to know where they are going, right?
This has been another area of focus for the Cluster mission, which for the last decade and a half has been attempting to explore how these ions are lost, where they come from, and the like. As Philippe Escoubet, ESA’s Project Scientist for the Cluster mission, put it:
“In essence, we need to figure out how cold plasma ends up at the magnetopause. There are a few different aspects to this; we need to know the processes involved in transporting it there, how these processes depend on the dynamic solar wind and the conditions of the magnetosphere, and where plasma is coming from in the first place – does it originate in the ionosphere, the plasmasphere, or somewhere else?“
Color illustration showing the scale of planets in our solar system, focusing on Jupiter and Saturn. Credit: NASA
The reasons for understanding this are clear. High energy particles, usually in the form of solar flares, can pose a threat to space-based technology. In addition, understanding how our atmosphere interacts with solar wind is also useful when it comes to space exploration in general. Consider our current efforts to locate life beyond our own planet in the Solar System. If there is one thing that decades of missions to nearby planets has taught us, it is that a planet’s atmosphere and magnetic environment are crucial in determining habitability.
Within close proximity to Earth, there are two examples of this: Mars, which has a thin atmosphere and is too cold; and Venus, who’s atmosphere is too dense and far too hot. In the outer Solar System, Saturn’s moon Titan continues to intrigue us, mainly because of the unusual atmosphere. As the only body with a nitrogen-rich atmosphere besides Earth, it is also the only known planet where liquid transfer takes place between the surface and the atmosphere – albeit with petrochemicals instead of water.
Moreover, NASA’s Juno mission will spend the next two years exploring Jupiter’s own magnetic field and atmosphere. This information will tell us much about the Solar System’s largest planet, but it is also hoped to shed some light on the history planetary formation in the Solar System.
In the past fifteen years, Cluster has been able to tell astronomers a great deal about how Earth’s atmosphere interacts with solar wind, and has helped to explore magnetic field phenomena that we have only begun to understand. And while there is much more to be learned, scientists agree that what has been uncovered so far would have been impossible without a mission like Cluster.
![Computer simulation of the Earth's field in a period of normal polarity between reversals.[1] The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of the Earth is centered and vertical. The dense clusters of lines are within the Earth's core](https://www.universetoday.com/wp-content/uploads/2010/03/Geodynamo_Between_Reversals-e1449100829326.gif)
