A plasma wave instrument (PWI), also known as a plasma wave receiver, is a device capable of detecting vibrations in outer space

plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...

and transforming them into audible sound waves or air vibrations that can be heard by the human ear. This instrument was pioneered by then-

University of Iowa The University of Iowa (UI, U of I, UIowa, or simply Iowa) is a public university, public research university in Iowa City, Iowa, United States. Founded in 1847, it is the oldest and largest university in the state. The University of Iowa is org ...

physics professor, Donald Gurnett. Plasma wave instruments are commonly employed on space probes such as

GEOTAIL Geotail was a satellite that observed the Earth's magnetosphere. It was developed by Japan's ISAS in association with the United States' NASA, and was launched by a Delta II rocket on 24 July 1992 from Cape Canaveral Air Force Station. The prim ...

Polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates * Polar climate, the c ...

, Voyager I and II (see

Plasma Wave Subsystem Plasma Wave Subsystem (sometimes called Plasma Wave System), abbreviated PWS, is an instrument that is on board the ''Voyager 1'' and ''Voyager 2'' unmanned probes of the Voyager program. The device is 16 channel step frequency receiver and a l ...

), and

Cassini–Huygens ''Cassini–Huygens'' ( ), commonly called ''Cassini'', was a space research, space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, i ...

Operating principle

Vibrations in the audible frequency range are perceived by humans when air vibrates against their

eardrum In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear The outer ear, external ear, or auris externa is the extern ...

. Air, or some other vibrating medium such as water, is essential for sound perception by the human ear. Without a medium to transmit it, the sound produced by a source will not be heard by a human. There is no air in outer space, nor is there any other type of medium capable of transmitting vibrations from a source to a human ear. However, there are sources in outer space that vibrate at frequencies audible to humans if only there were some transmitting medium to carry those vibrations from the source to a human eardrum. One such source capable of vibrating at audible frequencies (ranging from 45 to 20,000 vibrations per second) is plasma. Plasma is a collection of charged particles, such as free

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

s or

ionized Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...

gas atoms. Examples of plasma include

solar flare A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phe ...

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...

neon sign In the signage industry, neon signs are electric signs lighted by long luminous gas-discharge tubes that contain rarefied neon or other gases. They are the most common use for neon lighting, which was first demonstrated in a modern form in Decem ...

s, and

fluorescent lamp A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet lig ...

s. Plasma interacts with electrical and magnetic fields in ways that can result in vibrations across various frequencies, including the audible range.

Other applications

The recordings of interplanetary and outer space plasma vibrations, captured by plasma wave instruments, were provided by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

to composer

Terry Riley Terrence Mitchell "Terry" Riley (born June 24, 1935) is an American composer and performing musician best known as a pioneer of the minimalist school of composition. Influenced by jazz and Indian classical music, his music became notable for it ...

and Kronos quartet founder David Harrington as inspiration for the composition of "'' Sun Rings''", a 85-minute multimedia piece for a

string quartet The term string quartet can refer to either a type of musical composition or a group of four people who play them. Many composers from the mid-18th century onwards wrote string quartets. The associated musical ensemble consists of two violinists ...

and choir. "''Sun Rings''" was performed November 3, 2006, at the Veteran's Auditorium, in

Providence, Rhode Island Providence is the capital and most populous city of the U.S. state of Rhode Island. One of the oldest cities in New England, it was founded in 1636 by Roger Williams, a Reformed Baptist theologian and religious exile from the Massachusetts Bay ...

References

{{Reflist Plasma diagnostics Remote sensing Spacecraft instruments