Solar wind interactions

Scientists are able to study solar winds as they reach Earth's orbit, but to know how those winds interact with planets and other objects in the solar system requires scientists to understand the objects themselves and the nature of solar wind. The study of solar winds is important in terms of understanding the manner by which the sun's heat is carried to Earth, especially in an era of increasing reliance on telecommunications, satellite, and other technologies.

Basic Principles

Solar wind is the emission of superheated particles from the sun's corona (outer atmosphere). Although scientists have not conclusively determined the cause of this emission, what is known is that these particles (mainly electrons and protons) become so charged that the sun's gravity can no longer contain them. In some cases, this emission is known as a coronal mass ejection (CME), a sudden and violent release of the charged particles. Once released through coronal holes (dark regions within the corona that have an open magnetic field and low density), the winds travel as plasma away from the sun at varying speeds, sometimes as fast as 900 kilometers (560 miles) per second and with a temperature of 1.8 million degrees Fahrenheit.

Solar winds carry with them magnetic fields that, when interacting with Earth, can become trapped within Earth's magnetic field, causing a collision of these charged particles. These particles are visible as a natural light show known as the aurora. In some cases, solar winds cause geomagnetic storms, disturbances in Earth's magnetosphere (the field consisting of magnetically charged particles from both the sun and Earth) surrounding Earth. These storms can be severe enough to cause power outages and disruptions to cellular and satellite systems.

Background and History

In the early seventeenth century, the renowned German astronomer and mathematician Johannes Kepler noticed that the visible tails of comets, which consisted of dust, always seemed to point away from the sun regardless of their position. Kepler speculated that the pressure of sunlight that radiated outward caused such phenomena. Comets also have ion trails, visible in other light spectra (not just sunlight). These trails also point away from the sun, but with varying appearances. Some appear bent or appear to track in a different direction, suggesting that a force other than sunlight is at work.

In the 1940's, Germans astronomers Cuno Hoffmeister and Ludwig Biermann theorized that this force was solar corpuscular radiation, which worked at varying speeds and flow velocities. The Hoffmeister and Biermann theories worked to explain what this radiation was but failed to explain what caused it.

In 1958, solar astrophysicist Eugene Parker offered a different take on this phenomenon. He speculated that the sun, like Earth, had an atmosphere (the corona), but that the corona operated much more differently than that of Earth. As the intense heat generated by the sun reached the corona, Parker's theory posited, the outermost layers of the corona would be pushed away into space. The speed of this radiation would be determined by the temperature and by the distance traveled. Parker's model for solar wind was an ambitious approach but relied on a number of assumptions. In particular, the model determined that the corona's equilibrium (balance) was not in flux. Later theories asserted that Parker's model did not account for the variable speeds and intensities of solar winds.

Solar Wind and the Magnetosphere

Studying how solar winds form and interact with the magnetic fields of planets is a developing science. Solar winds are an even mix of highly charged protons and electrons that are emitted through coronal holes. These holes are found primarily at the sun's poles; on X-ray images of the sun's corona, they appear as dark, loose structures. These holes have low-level magnetic fields, which allow the hot gas to escape at high speed and radiate throughout the solar system in the form of solar wind. The area impacted by solar winds within the solar system is known as the heliosphere.

As they travel through space, solar winds (which possess magnetic fields) come into contact with the magnetic fields of other celestial bodies, including that of Earth. These winds ultimately affect Earth's magnetosphere (a broad area surrounding Earth's magnetic field that blocks highly charged particles from directly impacting the planet). Studies show that solar winds contribute to the shape of the magnetosphere, exerting pressure on it and reacting to the outward pressure it exerts as well. In 2005, three separate solar wind monitors in orbit captured a solar wind impact on the magnetosphere, demonstrating such an encounter. The event also was highlighted by a brief increase in strength of the ground-based magnetic field when the magnetosphere was pushed inward. When the magnetosphere stabilized, the ground-level magnetic field returned to normal levels.

Scientists also believe that solar winds that approach Earth's magnetosphere on a northward or southward track can cause a drag effect, tugging the magnetosphere away as particles within the wind connect with particles within the magnetosphere (a process known as reconnection). Experts continue to seek to understand the nature of reconnection and whether this process, as it occurs between solar winds and the magnetosphere, is a large-scale event or a patchier, small-scale phenomenon.

Solar Weather

The interaction between solar winds and objects within the heliosphere varies based on the strength of the magnetosphere, the speed and distance of the wind, and other factors. Earth has one of the strongest magnetospheres among the terrestrial (rocky) planets. Mars, however, does not have as strong a magnetosphere and, as a result, is subject to occasional geomagnetic storms (short-term solar weather disturbances in the magnetosphere) that are caused by solar winds. Data from the Mars Global Surveyor showed a number of such storms (periods of significant changes in the magnetic field at the surface level) taking place, some of which lasted nearly two full days and were severe in nature.

Earth's magnetosphere is one of the most durable regions in the solar system, but the planet is not immune to magnetic storms caused by the solar winds. Indeed, when the activity of sunspots (dark, cooler areas on the sun's surface that facilitate intense magnetic fields) is at a peak, solar winds are more intense. Magnetic storms with such severity can charge the particles within the magnetosphere, particularly within the two radiation belts (one of which is called the Van Allen belt, named for its discoverer, James Van Allen, in 1958). The protons and electrons that are trapped in these belts, energized by the solar winds, interact with the oxygen and nitrogen in Earth's atmosphere, causing a bright, multicolored hue in the polar regions (and sometimes regions closer to the equator) called the aurora. In more severe cases, however, solar storms have been known to cause electrical surges, blackouts, and major disruptions to telecommunications, satellite, and navigational systems. Adding to the risks is the fact that Earth's magnetic field flips every few hundred thousand years. It is unclear how solar winds will affect Earth should such a major shift occur.

Satellites

One of the most useful approaches to studying the solar winds and how they interact with the rest of the solar system is satellite technology. Such orbiting probes can be positioned outside the magnetospheres of their target of study and, as a result, provide data that are not susceptible to radio and magnetic interference. Some satellites are placed in a wide orbit of the sun, gathering data that have never before been seen. For example, in 2006, National Aeronautics and Space Administration (NASA) launched the Solar Terrestrial Relations Observatory (Stereo) probes. These two probes were placed in a wide orbit of the sun, one ahead of Earth's orbit and one behind. From this vantage point, Stereo has provided views of the far side of the sun, creating a three-dimensional image of the sun for the first time. The Stereo satellites have also been useful in studying CMEs and for recording the different speeds at which solar winds travel. Such research can lead to an early warning system for Earth, should a particular wind move with the intensity needed to create a geomagnetic storm.

Satellite technologies also are invaluable in observing the interactions between solar winds and Earth's magnetic field. In 2009, scientists used the German small satellite mission, Challenging Minisatellite Payload, to monitor the magnetic field above Earth's northern polar region from the lower atmosphere. This study created a new and previously unseen illustration of how the solar winds can influence Earth's upper atmosphere.

Telescopes

In addition to employing space-based systems and technologies, astronomers and astrophysicists frequently employ the use of ground-based telescopes (such as radio telescopes) to monitor coronal activity and to track solar winds. For example, scientists anticipate using the Advanced Technology Solar Telescope in Hawaii (Maui) and the Frequency-Agile Solar Radiotelescope in California to monitor magnetic activity on the sun and its transit through solar winds to Earth. Experts expect to use the two systems to create models of global magnetic fields as these fields interact with the solar winds.

Ground-based telescopes also are used in the observation of how solar winds interact with the magnetospheres of other planets. For example, astronomers have long shown interest in studying the causes of radio emissions of the planets in the solar system. Their hope is that by understanding the emissions of planets such as Jupiter, they may find a way to detect new planets. However, a 2007 radio-telescope study of the emissions of Jupiter and its moons revealed that many of their most pronounced radio emissions came not from within the magnetic fields of Jupiter and its moons but rather from intense solar winds and their effects on those objects. Therefore, tracking solar winds in the solar system and in other systems could also help scientists locate new planets.

Computer Models

In the study of solar winds, it is useful to study more than just the phenomena they foster (such as geomagnetic storms and aurora). Scientists recognize the need to also place these characteristics and occurrences into a broader and more intensive framework. It is in this capacity that computer models are deemed essential. For example, in 2011, scientists analyzed eight years (1998-2006) of solar wind occurrences, including CMEs and solar winds of varying intensity and velocity. Using a statistical program to compile data from these events (which included wind speed and similar characteristics), the resulting models can accurately predict the severity and scope of incoming solar winds.

The study of the interaction between solar winds and the planets and other objects of the solar system is not limited to just magnetic fields. Solar winds are believed to have played a major role in how much of the solar system appears today. Using advanced supercomputer models, NASA scientists recently completed a simulation of how dust particles carried on solar winds outward into the heliosphere formed the Kuiper belt (a large area near Neptune that contains millions of icy rocks and debris, including what was formerly considered a planet, Pluto). This simulation demonstrates how these particles were carried on solar winds to their current location and then collided with one another, forming larger, detectable objects.

Computer modeling systems, used in this arena, can help scientists consider how the solar system formed. Such models also can help scientists discover the existence of other objects within and beyond the solar system. Observing how the Kuiper belt was formed and how Neptune appeared during this period, astronomers can use these models to locate similar planetary systems.

Relevant Networks and Organizations

The study of the interaction between solar winds and objects in the solar system is critical to a wide range of public and private organizations and entities. For many in the scientific arena, an understanding of solar winds provides clues about how the solar system was formed, how it currently works, and how it will continue to develop. Others outside the scientific world look upon this field as useful in avoiding disruptions of the technologies on which twenty-first century civilization depends. Among the different groups that have a stake in understanding solar winds are governments, universities, and the global positioning systems industry.

Governments remain among the largest stakeholders in space exploration and astronomy. NASA, the European Space Agency, and other organizations are heavily reliant on the budget dollars that come from their respective national governments. From deep space probes to satellites to the ground-based Very Large Array radio-astronomy observatory (comprising twenty-seven massive radio antennae in New Mexico), government agencies such as NASA and the National Science Foundation are among the organizations exploring solar winds and their relationships with Earth and other planets.

Universities play an integral role not just in the study of existing data surrounding solar winds but also in providing the tools useful for such analyses. At the University of California, San Diego, for example, scientists have developed a three-dimensional modeling program that reconstructs the effects of solar winds on Earth's magnetic fields. This Solar Mass Ejection Imager creates a clear and comprehensive illustration of the behavior of charged particles that occurs when solar winds and the magnetosphere come into contact with one another. Such university-based technologies and, more important, the theories that arise from analyses of the data they produce, are essential to understanding solar winds.

Satellite-based global positioning devices have greatly benefited modern technology, but widespread reliance on this type of navigation means that a larger percentage of the population is at a loss when this worldwide network fails. A number of geomagnetic storms have cast a light on the vulnerability of the global positioning system (GPS). A 2006 storm, for example, affected receivers across half of the world. Such events have fostered a call within the GPS industry to locate ways to safeguard against large-scale outages. Few options exist, however, that are both proven and cost-effective. These ideas include altering the satellite antennae to filter solar signals or simply replacing all GPS satellites with ships with more broadcasting power.

Some experts are examining whether a lower orbit may provide answers. That is, by moving GPS satellites from the fringes of the magnetosphere, it may be possible to avoid significant disruptions caused by solar winds and some geomagnetic storms. However, research in this arena is ongoing, particularly as scientists examine the differences between orbits and how those differences affect service.

Implications and Future Prospects

The study of solar winds and how they interact with Earth and other planets continues to develop, particularly in light of the advances in astronomical technology, which have unveiled new information about these phenomena. In less than one-half century, humans have developed the ability to monitor solar activity, chart CMEs, and predict the arrival of the solar winds that travel through the heliosphere to their destination. Scientists have sent a number of probes throughout the solar system to monitor solar winds and their interactions with Mercury, Jupiter, Saturn, Earth's moon, and other celestial objects and planets.

The potentially destructive effects of solar winds on the technologies on which humanity is so dependent are also a driving force behind this field of study. Scientists are continually seeking ways to safeguard Earth's satellite systems and power grids from the geomagnetic storms that solar winds produce. As more and more segments of the economy become reliant on GPS, advanced telecommunications, satellite, and other technologies, the demand for an understanding of how space weather occurs and ways to avoid widespread disruptions and damage will likely continue.

Principal Terms

aurora: phenomenon in which highly charged particles in Earth's magnetic field generate a multicolored light show in the skies above the planet's polar regions (and sometimes farther south)

corona: the sun's outer atmosphere

geomagnetic storm: short-term disturbance in a planet's magnetosphere, frequently causing disruptions within the magnetic field

heliosphere: area within a solar system affected by the radiation emitted by the sun

magnetosphere: field consisting of magnetically charged particles from both the sun and Earth

radio telescope: instruments used to detect and track radio waves emanating from other planets and celestial bodies

solar wind: the emission of superheated particles from the sun's corona

Van Allen belt: one of Earth's two radiation belts located outside of Earth's atmosphere

Bibliography

Burch, James L. “The Fury of Solar Storms.” Scientific American 14, no. 4 (2004): 42-49. This article discusses how solar winds affect satellites and human space missions. The author cites a major solar flare and its effect on satellites in orbit of Earth.

Den Hond, Bas. “Scientists Predict GPS Failures.” Astronomy 34, no. 4 (2006). In this article, the author discusses the effects of solar storms on GPS satellites. Also outlines how charged particles in the ionosphere can disrupt the systems on which pilots and drivers alike rely for navigation.

Hanslmeier, Arnold. The Sun and Space Weather. 2d ed. New York: Springer, 2010. This book provides a review of the various forms of space weather, including magnetic storms and solar winds. The author also offers a synopsis of efforts to study such phenomena, including satellite and deep space missions and projects.

Miralles, Mari Paz, and Jorge Sanchez Almeida, eds. The Sun, the Solar Wind, and the Heliosphere. New York: Springer, 2011. This book features the findings of the International Association of Geomagnetism and Aeronomy's solar wind and interplanetary division. The volume discusses the sun's interior, the processes that exist throughout the heliosphere, the corona, and other aspects of the relationship between Earth and the sun.

Velli, Marco, Roberto Bruno, and Francesco Malara, eds. Solar Wind Ten: Proceedings of the 10th International Solar Wind Conference. College Park, Md.: American Institute of Physics, 2003. This conference discussed topics such as the physics of the sun's corona, the solar winds, and how the sun's emissions affect the objects of the heliosphere. Among areas examined were the sun's magnetic field, CMEs, and the geomagnetic effects of solar activity on planets and other celestial bodies.

Yakolev, O. I., J. Wickert, and V. A. Anufrief. “Effect of the Solar-Wind Shock Wave on the Polar Ionosphere According to the Radio Occultation Data on Satellite-to-Satellite Paths.” Doklady Physics 54, no. 8 (2009): 363-366. This article analyzes the effects of solar winds and solar storms have on the satellite systems in Earth's ionosphere.

Zubinaite, Vilma, and George Preiss. “Investigation of the Effects of Specific Solar Storming Events on GNSS Navigation Systems.” Aviation 15, no. 2 (2011): 44-48. Using Norway as a point of reference, the authors discuss the disruptive influences of solar winds on telecommunications and satellite systems in that region. The article also describes the reliance in this area on such twenty-first century technologies.