University of Iowa Logo
COLLEGE OF LIBERAL ARTS & SCIENCES
Department of Physics and Astronomy


iowa planeterrella
 



Home
People
Teaching
Research
Join Us
Publications
Support
Directions
Iowa Planeterrella

Demonstrations

planeterrella

A planeterrella is a contraption used to simulate space physics phenomena involving plasma and celestial bodies. The device consists of a bell jar inside which the air pressure can be pumped to approximately one ten-thousandth atmospheric pressure. Two metallic spheres containing permanent magnets are inside the bell jar and a power source is used to create an electric field between the spheres, or between either sphere and any of 4 metallic needles in the device.  This electric field causes electrons emitted from the surface of the metal to be energized to high enough energy to strip electrons off (ionize) of some of the neutral atoms present in the residual air, creating a plasma. This plasma interacts with the magnetic field from the magnets inside the spheres, in a similar manner to how plasma emitted from the sun (called the solar wind) interacts with Earth's magnetic field. Through modifying the arrangements of the magnets and the course of the electrons, we are able to reproduce such occurrences as the Aurora Borealis or Aurora Australis, the Van Allen radiation belts, stellar jets, coronal holes, and stellar ring currents.

The planeterrella at the University of Iowa is based off of a design conceived by Dr. Jean Lilensten of the Planetary and Astrophysical Institute of Grenoble in France: Planeterrella web page. In the Iowa Planeterrella, three modifications were made so that it could be incorporated into the Hawkeye's in Space museum exhibit. The first is an electronics switchboard that allows users to switch between different configurations by turning a knob (currently these are the radiation belt, aurora and ring current demonstrations). The second is an automated pressure control that maintains the pressure inside the device between a set range of values. Third, a clear Plexiglas box covers the bell jar so users cannot disturb it during use.  These modifications have enabled the device to be used by anyone without supervision.

The University of Iowa has long played a pioneering role in the exploration of space. It was here that James Van Allen worked to discover Earth’s radiation belts. Frontier research exploring space continues to be carried out by University of Iowa scientists using instruments built at the University of Iowa. To learn more about this ongoing research, please visit the Department of Physics and Astronomy faculty web pages.

The Iowa Planeterrella was constructed entirely by students. Master’s student Mr. Richard Bleckley and PhD student Mr. Ryan Hood constructed the base device in 2015. Undergraduate student Mr. Zachary Luppen made the modifications described above, to adapt it to the needs of the museum exhibit, in 2016. Construction was aided by the Department of Physics and Astronomy Electronics and Machine Shops.

Links:
Facebook page
All Planeterrellas

Aurora

aurora
(left) The aurora Borealis in a photograph taken from the international space station. Image credit: NASA. (right) Photograph of the aurora demonstration in the Iowa Planeterrella.

Aurora are created when the solar wind (a stream of charged particles coming from the Sun) becomes trapped by the Earth's magnetic field and can be deflected into the Earth's upper atmosphere toward the magnetic poles. The Earth is constantly in the flow of the solar wind, but when it’s stronger than usual, due to a solar storm or a solar flare, then the wind can be more powerful and cause the aurora to extend to lower latitudes.

The most powerful auroral event in modern times took place on August 28 - September 2, 1859 and was called the Carrington Event. If a similar event occurred today, it would cause widespread damage to modern technologies including satellites, power systems, and telecommunications. This threat has generated an increased interest in space weather forecasting.

Aurora are also present on other planets with magnetic fields and atmospheres. For example, they have been observed on Jupiter and Saturn.

Van Allen Radiation Belts

radiation belt
(left) Photo of the Van Allen radiation belts taken in the ultraviolet spectrum by the IMAGE satellite. Courtesy of NASA. (right) The Van Allen radiation belt demonstration using the Iowa Planeterrella.

The Van Allen radiation belts are layers of energetic charged particles held in place by the Earth’s magnetic field. These particles are thought to come from the solar wind and cosmic rays (very high-energy particles that come from outside the solar system). In 1958, the US launched Explorer 1; it’s first man-made satellite. This spacecraft carried the Iowa Cosmic Ray instrument, which was designed by University of Iowa Physics and Astronomy Professor James Van Allen. This instrument was the first to detect the radiation belts, which are now named in his honor.

Stellar Ring Current

ring current(left) Supernova Remnant 1987a (an exploded star), which displays the stellar ring current phenomenon. Image courtesy of NASA. (right) A demonstration of stellar ring currents using the Iowa Planeterrella.

A stellar ring current takes place when a star sends electrons all around itself and the magnetic field turns the electrons towards the equator, perpendicular to the magnetic axis of the star. While these do not take place at our Sun, this interesting phenomenon does occur near other classes of stars.

History

birkeland
Kristian Birkeland operating the first terrella experiment. Image in the public domain, from wikipedia.

A century ago, Norwegian scientist Kristian Birkeland (1867-1917) hypothesized that the aurora on Earth are caused by plasma streaming out from the Sun that gets trapped in the Earth’s magnetic field, causing currents in the polar regions of the upper atmosphere. To test this hypothesis, Birkeland led the “Norwegian Polar Expedition” from 1899 to 1900, which provided the first evidence (using ground based magnetic field measurements) of the current patterns in the polar region. Today, these are knows as the Birkeland currents. The existence of Birkeland currents was debated scientifically until a direct measurement was made in 1963 from the Navy satellite 1963-38C.

Upon returning from his expedition, Birkeland designed the “Terrella” experiment to study the interaction of plasma and magnetic fields in and effort to better understand the physics associated with the Earth-Sun interaction. Birkeland also made several other major contributions to science and technology. He invented the coil gun, and was the first to develop an industrial-scale method for nitrogen fixation from air (the Birkeland-Eyde process). Nitrogen fixation is the essential process needed to produce ammonia for farm fertilizer. Birkeland was nominated for a Nobel prize seven times. Learn more about Kristian Birkeland here.

Events

hawkeye's in space
The Iowa Planeterrella is currently on display at the: Hawkeye's In Space exhibit in the Old Capitol building on the University of Iowa campus.

Acknowledgments

nsf logo
Construction of the Iowa Planeterrella was supported by the US National Science Foundation under grant No. PHY-1453736. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the view of the National Science Foundation.