Van Allen Belts Protect Earth from Solar Wind
Geophysicists are still puzzling over how the earth’s magnetic field and Van Allen radiation belts protect the surface from deadly particles in the solar wind.
The Van Allen belts are lobes of high-energy particles above the atmosphere, formed as a consequence of the geomagnetic field. First discovered in 1958 by Dr James Van Allen of the University of Iowa, using instruments aboard the Explorer satellites designed by JPL spacecraft pioneer Dr. Henry Richter, these belts have long puzzled scientists. A pair of spacecraft called the Van Allen Probes have been gathering data about the belts since 2012. NASA’s Magnetospheric Multiscale Mission (MMS) also gathered data since 2015. Elizabeth Howell provides this overview of the Van Allen Belts on Space.com. She says,
On the 60th anniversary of Explorer 1, NASA said that studies of the Van Allen belts are even more important today. “Our current technology is ever more susceptible to these accelerated particles because even a single hit from a particle can upset our ever smaller instruments and electronics,” said David Sibeck, Van Allen Probes mission scientist at NASA’s Goddard Space Flight Center in Maryland, in a 2018 statement. “As technology advances, it’s actually becoming even more pressing to understand and predict our space environment.“
Here are additional news items about what these structures do for us.
Shock at the Bow
How Solar Wind Drops from Gale to Gentle Breeze as It Hits Earth’s Magnetic Field (University of Maryland). Animations of the solar wind often show particles streaming out from the sun directly at the earth, but our planet actually plows through the field along its orbital path, increasing the speed at which the particles impinge on our home were it not for planetary protection provided by the magnetic field. The press release explains,
As Earth orbits the sun at supersonic speed, it cuts a path through the solar wind. This fast stream of charged particles, or plasma, launched from the sun’s outer layers would bombard Earth’s atmosphere if not for the protection of Earth’s magnetic field.
Just as the nose of a motorboat creates a bow-shaped wave as it pushes through the water, Earth creates a similar effect—called a bow shock—as it pushes through the solar wind. A new University of Maryland-led study describes the first observations of the process of electron heating that happens in Earth’s bow shock.
The paper is published in Physical Review Letters. They found bad news before they understood the good news:
The researchers found that when the electrons in the solar wind encounter the bow shock, they momentarily accelerate to such a high speed that the electron stream becomes unstable and breaks down. This breakdown process robs the electrons of their high speed and converts the energy to heat….
“If you were to stand on a mountaintop, you might get knocked over by a fast wind,” explained Li-Jen Chen, lead author of the study and an associate research scientist in the UMD department of astronomy. “Fortunately, as the solar wind crashes into Earth’s magnetic field, the bow shock protects us by slowing down this wind and changing it to a nice, warm breeze. We now have a better idea how this happens.”
It’s not friction, therefore, that slows down the killer electrons; it’s breakdown of the electron stream due to instability. This is a new discovery from spacecraft measurements. “The study of electron heating is important not just for understanding how the bow shock protects Earth, but potentially for satellites, space travel and maybe exploring other planets in the future,” says Li-Jen Chen of the University of Maryland, lead author of the study. Her comment raises the question whether exoplanets could be habitable without such mechanisms. Richter’s book Spacecraft Earth raises the question whether a protective magnetic field could survive for millions of years.
Earth’s Magnetic Field is A Ruthless, Solar-Wind-Shredding Machine (Space.com). Brandon Specktor notes that the breakdown of the electron stream occurs in just 90 milliseconds – nine one-hundredths of a second. If it weren’t for this newly-discovered process, he says, earth would be fried:
Earth is constantly being bombarded by a hot, soupy plasma of protons, electrons and ions loosed by the sun in the form of solar wind. These winds blow all day and in all directions, blasting out of our nearest star at speeds of up to 500 miles per second (800 kilometers per second) and temperatures of up to 2.9 million degrees Fahrenheit (1.6 million degrees Celsius), according to NASA. You’d think that would be more than enough to bake our planet into a giant, orbiting lump of ash, but Earth and its atmosphere remain largely unscathed thanks to the planet’s strong magnetic field.
Scientists are still trying to understand these processes, the article ends. “But for now, enjoy the gentle winds of summer — and know, somewhere out there, that Earth’s magnetic field is violently ripping billions of solar electrons to bits on your behalf.”
Chirping Birds and Swing Pushers
What Causes Radiation Belt Enhancements: A Survey of the Van Allen Probes Era (Geophysical Research Letters). With an animation of electrons under the influence of the magnetic field, a press release from NASA-Goddard explains how electrons become excited within the belts.
Encircling Earth are two enormous rings — called the Van Allen radiation belts — of highly energized ions and electrons. Various processes can accelerate these particles to relativistic speeds, which endanger spacecraft unlucky enough to enter these giant bands of damaging radiation. Scientists had previously identified certain factors that might cause particles in the belts to become highly energized, but they had not known which cause dominates.
Now, with new research from NASA’s Van Allen Probes and Time History of Events and Macroscale Interactions during Substorms — THEMIS — missions, published in Geophysical Research Letters, the verdict is in. The main culprit is a process known as local acceleration, caused by electromagnetic waves called chorus waves. Named after their characteristic rising tones, reminiscent of chirping birds, chorus waves speed up the particles pushing them along like a steady hand repeatedly pushing a swing. This process wasn’t a widely accepted theory before the Van Allen Probes mission.
Radial Transport of Higher‐Energy Oxygen Ions Into the Deep Inner Magnetosphere Observed by Van Allen Probes (Geophysical Research Letters). “We suggest that the higher‐energy oxygen ions are transported to the inner magnetosphere selectively by the combination of two resonances: drift resonance and drift‐bounce resonance.”
Explaining the apparent impenetrable barrier to ultra-relativistic electrons in the outer Van Allen belt (Nature Communications).
Recent observations have shown the existence of an apparent impenetrable barrier at the inner edge of the ultra-relativistic outer electron radiation belt. This apparent impenetrable barrier has not been explained…. Contrary to earlier claims, sharp boundaries in fast loss processes at the barrier are not needed. Moreover, we show that penetration to the barrier can occur on the timescale of days rather than years as previously reported, with the Earthward extent of the belt being limited by the finite duration of strong solar wind driving, which can encompass only a single geomagnetic storm.
Update 6/12/18: Astrobiology Magazine reports that European Space Agency (ESA) scientists are seeking to understand how the solar wind impacts rocks on the moon and Mercury. Most solar wind particles consist of hydrogen ions (protons) and helium ions, but some heavier atoms are in the mix, too. These particles can impact surface rocks at speeds of 400 to 800 km per second, shattering the rock and dislodging atoms in a process called sputtering. The erosional damage does not affect Earth:
The planets and moons of our solar system are continuously being bombarded by particles hurled away from the sun. On Earth this has hardly any effect, apart from the fascinating northern lights, because the dense atmosphere and the magnetic field of the Earth protect us from these solar wind particles. But on the Moon or on Mercury things are different: There, the uppermost layer of rock is gradually eroded by the impact of sun particles.
Constant bombardment and liberation of particles by sputtering creates a thin “exosphere” around the moon and Mercury that scientists can study remotely for clues about surface composition. “The effects of solar wind bombardment are in some cases much more drastic than previously thought,” the article explains, because heavier elements not only have more mass but can carry multiple levels of charge (i.e., they lack several electrons). Their impact on a surface can atomize rocks in a flash of kinetic and electrical energy.
The article notes that “the uppermost layer of rock is gradually eroded by the impact of sun particles,” but did not mention what effects could be expected over millions or billions of years. The ESA’s first mission to Mercury, called BepiColombo is scheduled for launch in October 2018.
We need to keep in mind these physical mechanisms as we “enjoy the gentle winds of summer,” realizing that multiple laws of physics and chemistry appear to have ‘conspired’ to work together for our benefit. Secular scientists would have us believe that there are so many stars and planets, life must be commonplace. They have a very permissive view of what chance can accomplish, both biologically and physically. In Spacecraft Earth, Dr. Richter identifies some 15 factors that work together to make our planet habitable. Using reasonable estimates of probability, he estimates that less than one planet in the universe would have all 15 factors! Of course, we know there is at least one. But is it reasonable to assume that habitable planets are a dime a dozen?
Think how uncanny it is that physical processes that have nothing to do with life, like bow shocks and chorus waves, would play a role in protecting life far below, on the surface of a planet out of the range of their operations. The same argument could be made for physical processes under the earth’s surface, such as mineral transport and plate tectonics, and for physical processes within the biosphere, such as ocean currents and atmospheric circulation patterns. Additionally, there are astronomical considerations that make earth habitable, such as having the right kind of star, being the right distance from it, and having an axial tilt that gives rise to seassons. This doesn’t look like a haphazard arrangement of independent mindless processes. It supports what the Lord revealed in Isaiah 45:18
For thus says the Lord, who created the heavens (he is God!), who formed the earth and made it (he established it; he did not create it empty, he formed it to be inhabited!): “I am the Lord, and there is no other.”