AUTHOR: Russ Nelson
Newswise — Solar flares and coronal mass ejections (CMEs) are two of the most energetic processes in the solar system, showering Earth’s magnetic field with billions of tons of high-energy plasma gas, potentially disrupting power grids, satellites and communications networks. Understanding the fundamental particle acceleration process involved in large solar energetic particle (SEP) events such as these is one of the central problems in heliophysics research.
Dr. Gang Li, a professor in the Department of Space Sciences at the University of Alabama at Huntsville (UAH), is the first author of a paper in The Astrophysical Journal titled “Modeling solar energetic neutral atoms from CME-driven solar flares and shocks that demonstrates—for the first time—how energetic neutral atoms, or ENAs, can be used as a new tool to study the acceleration process in large SEP events, as well as distinguish between the two sites of acceleration: large chains in solar flares and aftershocks , induced by CMEs.
“This work is likely to excite [heliophysics] community to think more about the generation and propagation of solar ENA particles,” says Dr Li. “The paper demonstrates for the first time that ENAs can be used to distinguish between CME/Flare SEP acceleration, laying the necessary theoretical foundation for a possible future measurement of solar ENAs.”
The researcher’s work at UAH, part of the University of Alabama system, is supported by two NASA Living With Stars grants, as well as a grant from the National Science Foundation.
“Dr. Li’s work provides a revolutionary new approach to remotely study the physics of particle acceleration in the Sun’s atmosphere,” said Dr. Gary Zank, director of UAH’s Space Plasma and Aeronautical Research Center and chairman of Aerojet Rocketdyne to Department of Space Science.” This expands the already significant efforts at the Department of Space Sciences to use ENAs to study remote regions of the heliosphere, where we use ENAs created at the far boundaries of the heliosphere and the neighboring interstellar medium to study the plasma physics of these regions.”
“The ultimate goal of using ENAs is to obtain different physical parameters of the acceleration sites,” notes Dr. Li. “Scientists know that particles can be accelerated in two possible places: either solar flares or a CME-driven shock. But which location is more efficient at accelerating particles? Which place can accelerate particles to higher energies? These are often debated questions and we don’t know the answer.
The main barrier to resolving these mysteries through experimental observation is the Sun itself, as a basic understanding of the near-solar conditions and physical processes involved in the production of SEP events is hampered by the inability to make direct measurements near the acceleration sites.
ENAs represent a potential new method for providing answers because they are neutral particles (hydrogen atoms) that form from protons from exchange-change reactions. Being neutral, they are not affected by magnetic fields.
“This is very important because these neutral particles are not affected by the MHD of the solar wind [magnetohydrodynamic] turbulence as they propagate from the Sun to the observers,” explains Dr Li. “By comparison, protons, ions and electrons, because they are charged, their propagation from the Sun to Earth is distorted by the magnetic field of the solar wind. Therefore, ENAs carry all the information about the physics of the acceleration site. So observing them offers an entirely new opportunity to constrain the fundamental process of particle acceleration.
Also, energetic atoms can reveal their secrets at a distance of 1 AU or about 150 million kilometers from the Sun, where the ENA flux is at a level that can still be measured by a dedicated ENA detector. The quest to mine this data could eventually lead to a new NASA solar mission to better understand these particles and how large SEP events arise to affect Earth’s magnetosphere.
“Our simulation forms a theoretical basis for interpreting future ENA observations,” notes Dr. Li. “Similar observations are likely on NASA’s radar as a future mission, such as NASA’s SMEX mission, to be dedicated to solar ENA research. A special ENA mission that filters out the more numerous charged SEPs and goes directly after these ENA measurements could provide new information on SEP acceleration near the Sun and help resolve long-standing questions that have baffled the community.
In fact, a new NASA mission in which Dr. Zanck is a co-investigator called IMAP (Interstellar Mapping and Acceleration Probe) will actually have ENA instruments at 1 AU capable of measuring ENAs created both at the far reaches of heliosphere and also originating from the Sun.