New Method for Studying Solar Flares and Coronal Mass Ejections

This schematic diagram illustrates the two acceleration sites of ions in large solar energetic particle (SEP) events: flares and CME-driven shocks. Once produced, energetic ions can propagate along open interplanetary magnetic field (IMF) lines and be detected in-situ at 1 astronomical unit, or 150 million kilometers. The density of solar atmosphere near the acceleration sites is high enough so that energetic ions can lead to the production of solar ENAs. Credit: Gang Li/University of Alabama in Huntsville

Solar flares and coronal mass ejections (CME) have long been known as highly energetic phenomena in the solar system, with the potential to disrupt various technological systems on Earth. The study of these events and the underlying particle acceleration processes involved has been a significant challenge for researchers in the field of heliophysics. However, a groundbreaking paper titled "Modeling Solar Energetic Neutral Atoms from Solar Flares and CME-driven Shocks," authored by Dr. Gang Li from The University of Alabama in Huntsville (UAH), introduces a promising new approach. The research demonstrates how energetic neutral atoms (ENAs) can be utilized to study the acceleration process in solar energetic particle (SEP) events, distinguishing between the acceleration sites of solar flares and CME-driven shocks.

A Breakthrough in Heliophysics Research

Dr. Li's research represents a significant breakthrough in heliophysics, providing a new method to remotely explore particle acceleration in the sun's atmosphere. By using ENAs, which are neutral hydrogen atoms formed from protons through charge exchange reactions, researchers can bypass the limitations posed by the sun's near conditions and directly measure the acceleration sites. Unlike charged particles such as protons, ions, and electrons, ENAs are not affected by magnetic fields. This characteristic allows them to carry valuable information about the acceleration process from the sun to Earth without distortion from solar wind magnetic fields.

Dr. Gary Zank, the director of UAH's Center for Space Plasma and Aeronomic Research, acknowledges the significance of Dr. Li's work, stating that it opens up new avenues for studying remote regions of the heliosphere. While ENAs have been previously employed to explore the plasma physics of distant boundaries within the heliosphere, Dr. Li's research expands the application of ENAs to study solar acceleration sites.

Unraveling the Mysteries of Particle Acceleration

One of the key objectives of using ENAs is to obtain critical physics parameters at the acceleration sites, which will shed light on the efficiency and energy levels achieved by particle acceleration in solar flares and CME-driven shocks. The scientific community has been engaged in a longstanding debate regarding which site is more efficient in accelerating particles and capable of reaching higher energies. These questions have remained unanswered due to the lack of direct measurements near the acceleration sites. However, with the theoretical groundwork established by Dr. Li's research, the possibility of future ENA measurements offers a pathway to solve these mysteries.

The Role of ENA Observations

ENA observations hold tremendous potential in providing crucial insights into solar particle acceleration. As neutral particles, ENAs are not influenced by solar wind magnetohydrodynamic turbulence during their propagation from the sun to observers. This unique characteristic allows ENAs to carry comprehensive physics information about the acceleration sites, making them invaluable for studying solar flares and CME-driven shocks. The data retrieved through ENA observations can contribute to the development of a new NASA solar mission focused on understanding these particles and their impact on Earth's magnetosphere.

Future ENA Missions and NASA's Involvement

Dr. Li emphasizes that their research forms a theoretical basis for interpreting future ENA observations. It is highly likely that NASA will prioritize such observations as part of a future mission, such as the NASA SMEX mission, specifically dedicated to solar ENA studies. A dedicated ENA mission equipped with advanced detectors capable of filtering out charged SEPs and focusing solely on ENA measurements would provide unprecedented information about SEP acceleration near the sun. This mission could potentially address longstanding questions that have perplexed the scientific community.

In fact, NASA's upcoming mission, the Interstellar Mapping and Acceleration Probe (IMAP), in which Dr. Gary Zank, a co-investigator, is involved, will feature ENA instruments at 1 astronomical unit capable of measuring ENAs created in the distant reaches of the heliosphere and originating from the sun. This mission, known as IMAP, represents NASA's commitment to advancing the understanding of solar particle acceleration and interstellar mapping.

Journal Information: Gang Li et al, Modeling Solar Energetic Neutral Atoms from Solar Flares and CME-driven Shocks, The Astrophysical Journal (2023). DOI: 10.3847/1538-4357/acb494