Anthropogenic effects on the space environment started in the late 19th century and reached their peak in the 1960s when high-altitude nuclear explosions were carried out by several countries. These explosions created artificial radiation belts near Earth that resulted in major damages to satellites. Another, unexpected impact of the high-altitude nuclear tests was the electromagnetic pulse.
Other anthropogenic impacts on the space environment include chemical release experiments, high-frequency wave heating of the ionosphere and the interaction of VLF (very low frequency) waves with the radiation belts.
In a paper recently published in the journal Space Science Reviews, researchers reviewed the fundamental physical process behind these phenomena and discussed the observations of their impacts.
Space Weather Events Linked to High-Altitude Nuclear Explosions
From 1958 to 1962, the U.S. and the Soviet Union ran high-altitude tests with exotic code names like Starfish, Argus and Teak. The tests have long since ended, and the goals at the time were military. Today, however, they can provide crucial information on how humans can affect space.
“The tests were a human-generated and extreme example of some of the space weather effects frequently caused by the Sun,” said co-author Dr. Phil Erickson, assistant director at the MIT Haystack Observatory.
“If we understand what happened in the somewhat controlled and extreme event that was caused by one of these man-made events, we can more easily understand the natural variation in the near-space environment.”
Space weather is typically driven by external factors. The Sun sends out millions of high-energy particles, the solar wind, which races out across the Solar System before encountering Earth and its magnetosphere, a protective magnetic field surrounding the planet.
Most of the charged particles are deflected, but some make their way into near-Earth space and can impact our satellites by damaging onboard electronics and disrupting communications or navigation signals.
These particles, along with electromagnetic energy that accompanies them, can also cause auroras, while changes in the magnetic field can induce currents that damage power grids.
The Cold War tests, which detonated explosives at heights from 16 to 250 miles above the surface, mimicked some of these natural effects. Upon detonation, a first blast wave expelled an expanding fireball of plasma, a hot gas of electrically charged particles. This created a geomagnetic disturbance, which distorted Earth’s magnetic field lines and induced an electric field on the surface.
Some of the tests even created artificial radiation belts, akin to the natural Van Allen radiation belts, a layer of charged particles held in place by Earth’s magnetic fields.
Other tests mimicked other natural phenomena we see in space. The Teak test, which took place on Aug. 1, 1958, was notable for the artificial aurora that resulted. The test was conducted over Johnston Island in the Pacific Ocean.
On the same day, the Apia Observatory in Western Samoa observed a highly unusual aurora, which are typically only observed in at the poles. The energetic particles released by the test likely followed Earth’s magnetic field lines to the Polynesian island nation, inducing the aurora. Observing how the tests caused aurora, can provide insight into what the natural auroral mechanisms are too.
Later that same year, when the Argus tests were conducted, effects were seen around the world.
These tests were conducted at higher altitudes than previous tests, allowing the particles to travel farther around Earth.
Sudden geomagnetic storms were observed from Sweden to Arizona and scientists used the observed time of the events to determine the speed at which the particles from the explosion traveled.
They observed two high-speed waves: the first traveled at 1,860 miles per second and the second, less than a fourth that speed. Unlike the artificial radiation belts, these geomagnetic effects were short-lived, lasting only seconds.
Such atmospheric nuclear testing has long since stopped, and the present space environment remains dominated by natural phenomena.
However, considering such historical events allows scientists and engineers to understand the effects of space weather on our infrastructure and technical systems.
NASA’s Van Allen Probes Find Anthropogenic Bubble Shrouding Earth
VLF radio communications have been found to interact with particles in space, affecting how and where they move. At times, these interactions can create a barrier around Earth against natural high energy particle radiation in space, according to Dr. Erickson and co-authors.
VLF signals are transmitted from ground stations at huge powers to communicate with submarines deep in the ocean.
While these waves are intended for communications below the surface, they also extend out beyond our atmosphere, shrouding Earth in a VLF bubble.
This bubble is even seen by spacecraft high above Earth’s surface, such as NASA’s Van Allen Probes.
The probes have noticed an interesting coincidence — the outward extent of the VLF bubble corresponds almost exactly to the inner edge of the Van Allen radiation belts, a layer of charged particles held in place by Earth’s magnetic fields.
Professor Dan Baker, co-author of the paper and director of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, coined this lower limit the ‘impenetrable barrier’ and speculates that if there were no human VLF transmissions, the boundary would likely stretch closer to Earth.
Indeed, comparisons of the modern extent of the radiation belts from Van Allen Probe data show the inner boundary to be much farther away than its recorded position in satellite data from the 1960s, when VLF transmissions were more limited.
With further study, VLF transmissions may serve as a way to remove excess radiation from the near-Earth environment.
“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,” Dr. Erickson said.
T.I. Gombosi et al. Anthropogenic Space Weather. Space Sci Rev, published online April 13, 2017; doi: 10.1007/s11214-017-0357-5
This article is based on text provided by the National Aeronautics and Space Administration.