Tracing a Multi-Temperature Quiescent Prominence's Thermodynamic Evolution from Sun to Earth

Solar prominences are cool, dense stable structures routinely observed in the corona. Prominences are often ejected from the Sun via coronal mass ejections (CMEs). However, they are rarely detected in a cool, low-ionized state within CMEs measured in situ, making their evolution hard to study. We examine the thermodynamic evolution of one of these rare cases where a quiescent prominence eruption clearly preserves its low-ionized charge state as evidenced by in situ detection. We use multi-viewpoint Extreme Ultraviolet (EUV) observations to track and estimate the density, temperature and speed of the prominence as it erupts. We observe that part of the prominence remains in absorption well beyond initial liftoff, indicating the bulk of the prominence experiences minimal ionization and suggesting any strong heating is balanced by radiative losses, expansion, or conduction. From its subsequent in situ passage near 1au, charge states reveal that the prominence is composed of both cool, low-ionized ions as well as hotter plasma reflected by the presence of highly ionized iron, Fe$^{16+}$. Simulated non-equilibrium ionization and recombination results using observationally derived initial conditions match the in situ multi-thermal state for a prominence composed of 70% cool plasma with a 1.8MK peak temperature, and 30% hot plasma with a 4.3MK peak temperature. This suggests that the prominence may not be heated uniformly or that parts of it cools more rapidly. The complex, multi-thermal nature of this erupting prominence emphasizes the need for more comprehensive spectral observations of the global corona.

💡 Research Summary

Solar prominences are dense, relatively cool structures embedded within the hot solar corona. These structures are frequently ejected from the Sun as part of Coronal Mass Ejections (CMEs). A significant challenge in solar physics is the difficulty of tracking the thermodynamic evolution of these prominences; during their transit from the Sun to Earth, the low-ionized, cool state characteristic of prominences is typically lost due to ionization processes, making in-situ detection of their original state extremely rare.

This study presents a detailed analysis of a rare event where a quiescent prominence preserved its low-ionized charge state throughout its journey to 1 au. By utilizing multi-viewpoint Extreme Ultraviolet (EUV) observations, the researchers were able to track the physical evolution of the prominence during its initial eruption phase, estimating critical parameters such as density, temperature, and velocity. A key observation from the EUV data was that portions of the prominence remained in an absorption state well after the initial liftoff. This suggests a delicate thermodynamic balance where any heating—whether from conduction or radiation—was effectively offset by radiative losses or expansion-driven cooling, preventing rapid ionization.

The study further bridged the gap between solar-surface observations and in-situ measurements near Earth. The in-situ data revealed a complex, multi-thermal plasma composition, characterized by the simultaneous presence of low-ionized ions and highly ionized species, specifically Fe$^{16+}$. To interpret this coexistence, the researchers employed simulations of non-equilibrium ionization and recombination using the initial conditions derived from the EUV observations. The results of these simulations closely matched the in-situ multi-thermal state, revealing that the prominence was composed of approximately 70% cool plasma (with a peak temperature of 1.8 MK) and 30% hot plasma (with a peak temperature of 4.3 MK).

The findings indicate that the thermodynamic evolution of an erupting prominence is not a uniform process. The existence of such a multi-thermal structure suggests that heating and cooling mechanisms act heterogeneously across the prominence, or that certain regions undergo much more rapid cooling than others. This research underscores the complexity of the solar corona’s thermal landscape and highlights the urgent need for more comprehensive and high-resolution spectral observations to fully understand the global dynamics of the solar corona and the evolution of eruptive structures.