Ninety-nine percent of the observable universe is in the plasma state, which is often referred to as the “fourth state of matter.” Plasmas are collections of electrically charged particles, ions and electrons, whose behavior is controlled by electric and magnetic fields and which can generate and carry powerful electrical currents. All solar system bodies—the planets, their moons, asteroids, comets—are immersed in a magnetized plasma, either the solar wind or the plasma confined within a planetary magnetosphere (the region of space dominated by a planet’s magnetic field). Heliophysics seeks to characterize and understand the physical processes operating in these various plasma environments.
Our research involves:
- Measuring the space plasma environment throughout the solar system
- Inventing, designing, building, and testing the next generation of space instrumentation (space plasma and energetic particle instruments, energetic neutral atom cameras, mass spectrometers, ultraviolet imagers)
- Conducting experiments in state of the art laboratories
- Analyzing past and current mission data to uncover the fundamental processes controlling the space environment
Our science topics include:
- The structure and dynamics of the solar wind and the interstellar boundary
- Magnetic reconnection and solar-wind-magnetosphere interactions
- Magnetospheric and plasma physics at Earth, Mercury, Jupiter, Saturn, and Pluto
- Plasma-atmosphere interactions at Mars, Venus, Titan, comet Churyumov-Gerasimenko, and Enceladus
- Fundamental plasma physics research throughout the heliosphere and beyond.
- Statistical mechanics of space charged particle systems out of thermal equilibrium
Since the beginning of our space research program in 1977, SwRI scientists have been actively involved in the international space science community’s efforts to characterize and understand Earth’s magnetospheric environment. SwRI led NASA’s Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission, the first mission to obtain global images of the major plasma regions of Earth’s magnetosphere. The Institute currently leads the science investigation for NASA’s Magnetospheric Multiscale (MMS) mission, a four-spacecraft mission to probe the microphysics of magnetic reconnection. This fundamental process converts the energy stored in magnetic fields into the kinetic energy of charged particles and heat. Through the merging of the Sun’s magnetic field (carried by the solar wind) with the terrestrial magnetic field, reconnection “powers” Earth’s magnetosphere, driving the flow of plasma and producing occasional space weather “storms.” Such space weather disturbances manifest themselves benignly in the northern and southern lights; when severe, however, magnetospheric storms can shut down electrical power grids and disrupt satellite-based communication and navigation systems.
Other Solar System Plasma Environments
SwRI’s heliophysics research program encompasses more than terrestrial magnetospheric physics and includes studies of the magnetospheres of Jupiter and Saturn as well as investigations of the solar wind and its interactions both with unmagnetized or weakly magnetized solar system bodies.
- The SwRI-led Juno mission arrived at Jupiter in July 2016 and is now in a polar orbit around the gas giant. One of the scientific objectives of the Juno mission is to investigate Jupiter’s aurora and to compare the processes that power it with those responsible for the northern and southern lights here on Earth. To help achieve this objective, Juno’s scientific payload includes three SwRI-built instruments: an ultraviolet spectrograph to image and characterize the jovian aurora and two plasma instruments to measure the precipitating magnetospheric electrons and ions that excite the auroral emissions.
- The Cassini Saturn Orbiter’s 13-year exploration of the Saturn system will end in the fall of 2017, when the probe makes a controlled dive into the gas giant’s atmosphere and burns up. During much of the mission, the SwRI-developed Cassini Plasma Spectrometer or CAPS instrument provided a wealth of data on the sources, properties, and circulation of plasma within Saturn’s magnetosphere and on the interaction of Saturn’s magnetospheric plasma with the dense atmosphere of the planet’s largest moon Titan as well as with the tenuous atmospheres and surfaces of the smaller icy moons.
- SwRI-built instruments have also been employed to study the interaction of a magnetized plasma with unmagnetized or weakly magnetized solar system bodies other than Saturn’s moons. As part of the five-instrument Rosetta Plasma Consortium, SwRI’s Ion and Electron Sensor (IES) gathered data on the solar wind interaction with the nucleus and coma of comet 67P/Churyumov-Gerasimenko as it traveled from beyond the orbit of Mars toward perihelion. During the historic Pluto flyby in 2015, the New Horizon’s Solar Wind Analyzer for Pluto (SWAP) experiment made the first-ever observations of the solar wind’s interaction with Pluto’s atmosphere, revealing a “tail” formed by ions escaping from Pluto’s atmosphere and extending more than one hundred thousand kilometers beyond the planet. The solar wind/atmosphere interaction at Mars and Venus has been investigated with the help of SwRI-provided sensors as part of the ASPERA instrument package on ESA’s ongoing Mars Express mission as well as on the recently ended Venus Express mission. This interaction affects upper atmospheric composition, chemistry, structure, and energetics and leads to the loss of atmospheric material, which can be substantial over the lifetime of a planet whose atmosphere is not protected by a strong magnetic field.
Solar and Heliospheric Physics
As its name implies, a central theme of heliophysics concerns the Sun and its influence throughout the solar system. This influence is exercised through both the Sun’s radiative output and the solar wind—the supersonic outflow of plasma from the Sun’s upper atmosphere or corona. The solar wind flows throughout the solar system and inflates a giant bubble within the Local Interstellar Medium (LISM) known as the heliosphere. Especially during times of increased solar activity, the quasi-steady flow of the solar wind is disturbed by magnetic reconnection-driven eruptive events—solar flares and coronal mass ejections. These solar storms produce highly energetic particles and can trigger severe magnetospheric disturbances. Understanding and characterizing such events is critically important to forecasting space weather and mitigating its effects.
- Scientists have still not determined why the corona is thousands of times hotter than the visible surface of the Sun and how the solar wind is accelerated. The Institute is a key participant in two missions designed to answer both of these fundamental questions: NASA’s Solar Probe Plus (SPP+)and ESA’s Solar Orbiter, both scheduled for launch in 2018. SwRI scientists are involved in the development of an investigation on SPP+ to study the production of highly energetic charged particles. Our staff is also building one of the instruments in the Solar Wind Analyzer suite for the Solar Orbiter mission.
- SwRI researchers are engaged in the analysis of in-situ solar and heliospheric data from a variety of sources, characterizing, for example, long-term trends in the properties of the solar wind, investigating the acceleration of solar energetic particles by CME-driven shocks, and examining the production of energetic particles at co-rotating interaction regions in the solar wind.
- Heliospheric imaging is another focus area in SwRI’s space science research program. Innovative imaging processing and analysis techniques developed at the Institute in collaboration with colleagues are enabling researchers to explore the transition region between the corona and the solar wind and to trace the evolution of structures in the solar wind as they propagate from their origin in the corona through the inner heliosphere.
- Using energetic neutral atom (ENA) imaging techniques similar to those employed on the IMAGE and TWINS missions, the SwRI-led Interstellar Boundary Explorer (IBEX) mission obtained the first-ever global images of the region where the solar wind encounters and interacts with the local interstellar medium. The IBEX images revealed a totally unexpected feature—a “ribbon” of bright ENA emissions draped along the nose of the heliopause, the boundary that separates the heliosphere from the LISM. Subsequent data analysis and modeling efforts have focused on assessing the various theories proposed to explain this mysterious structure. IBEX data have allowed researchers to determine the tail-like structure of the heliosphere in the downwind direction, establish the magnitude and direction of the interstellar magnetic field, and derive the direction and temperature of the interstellar wind as it flows through the heliosphere.