Data from the solar active region NOAA 11861 has provided invaluable insights, contributing to a significant advancement in understanding H2 behavior in the Sun's lower atmosphere. Led by Dr. Sarah Jaeggli of the NSF National Solar Observatory (NSO), researchers identified 37 new H2 emission lines through FUV observations captured by IRIS. This discovery provides a richer understanding of the lower atmospheric structure during solar flare events.

Emission lines are created when atoms or molecules absorb energy and subsequently emit light as they revert to a lower energy state. These lines help identify and study different materials present in the Sun's atmosphere. The fluorescence of H2, which is similar to the effect of a black light on neon colors, becomes visible when solar radiation excites the molecule.

Dr. Jaeggli, collaborating with NASA Goddard Space Flight Center's Dr. Adrian Daw, confirmed the newly observed H2 lines by cross-referencing with synthetic spectra of H2 fluorescence. This method ensured accurate identification, avoiding errors and aligning findings with prior atomic line data.

Highlights from Spatially Resolved H2 Emissions
Key discoveries from the spatially resolved analysis of H2 emissions include:

Optically Thick Formation: Unlike previous conclusions, the spatially resolved data indicated that H2 emission lines are likely formed in optically thick regions, where photons undergo multiple reabsorptions and emissions before escaping. This points to denser atmospheric origins for these lines.

Probing Intermediate Atmospheric Depths: Comparisons between H2 Doppler velocities and those of other elements revealed that H2 emissions investigate an intermediate depth between the photosphere and chromosphere, matching atmospheric model predictions. This depth is essential for understanding vertical atmospheric structures during flare events.

Temperature-Sensitive Fluorescence: The relative intensity of H2 emission lines depends on local atmospheric temperatures, showing that H2 fluorescence can act as a diagnostic tool for assessing thermal variations during flares.

Remote Excitation Phenomenon: A surprising outcome was the discovery that H2 fluorescence could be stimulated by radiation from sources located several megameters away on the solar surface. This finding suggests that H2 emissions respond not only to local but also to wider solar dynamics.

Research Implications for Solar Studies
These insights have a considerable impact on our understanding of the Sun's lower atmosphere. Identifying new H2 lines and understanding their formation offers a clearer view of the intermediate atmospheric layers affected during solar flares. The presence of molecules in significant numbers could alter fundamental solar plasma processes, highlighting the need for their inclusion in solar models.

Dr. Jaeggli emphasized, "for the most part, molecules are ignored in the physics of the Sun, included in simulations, but they might be important in very cool regions, in which case, we are modeling the Sun wrong by excluding them."

As observational technology progresses, analyzing H2 emissions will remain a key method for dissecting the Sun's atmospheric complexities. These findings not only deepen knowledge in solar physics but also enhance the ability to forecast and interpret solar activity, impacting space weather predictions and broader astrophysics research.

Research Report:Molecular Hydrogen Line Identifications in Solar Flares Observed by IRIS: Lower Atmospheric Structure from Radiometric Analysis

Related Links
National Solar Observatory
Solar Science News at SpaceDaily