On the Ubiquity and Physical Nature of Fe ix 17.1 nm Moss
- 1Naval Research Laboratory
Abstract
The spongy Fe ix 17.1 nm fine structure known as “moss” was first detected inside active region (AR) plages and has been widely interpreted as representing the transition region of the overlying hot coronal loops. However, 17.1 nm images show that similar reticulated structure is present at lower intensity levels everywhere on the Sun outside of coronal holes, although its presence in weak-field and internetwork regions is often masked by the overlying fibrils. In the quiet Sun, the moss tends to be clustered around the bases of Fe xii 19.3 nm loops, with continual jet-like ejections being observed along their stalks. Depending in part on the viewing angle, the curved structures surrounding the “holes” in the moss often resemble small, highly dynamic loops with sizes of ∼2–5 Mm. We discuss two different physical interpretations of the moss. First, in line with the traditional view, it may represent the transition region of coronal loops both inside and outside ARs, with heat being conducted downward into the moss from greater heights and the dark holes representing the spaces between the heated footpoints. An alternative interpretation is that the moss consists mainly of small loops that continually undergo magnetic reconnection with the overlying coronal field, with the associated heating rate depending on the local field strength. This scenario is supported by the tendency for the moss to spill over into weak internetwork regions and by the continual jetting activity observed from network flux concentrations.
Related
- A critical evaluation of the physical nature of the little red dots
- Physical assumptions versus nature: the shape of the heliosphere
- The Ubiquity of White-Light Flares on the Sun
- MOSS III: MeerKATs view on the galaxy populations in two massive galaxy clusters
- Something green beneath the surface: The dynamical nature of fossil structures in IllustrisTNG-100
BibTeX
@article{wang2026ubiquity,
title = {{On the Ubiquity and Physical Nature of Fe ix 17.1 nm Moss}},
author = {Y.-M. Wang and I. Ugarte-Urra and H. P. Warren},
journal = {The Astrophysical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-4357/aea0ce},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea0ce},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - On the Ubiquity and Physical Nature of Fe ix 17.1 nm Moss
AU - Y.-M. Wang
AU - I. Ugarte-Urra
AU - H. P. Warren
PY - 2026
DA - 2026/10/15
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aea0ce
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aea0ce
AB - The spongy Fe ix 17.1 nm fine structure known as “moss” was first detected inside active region (AR) plages and has been widely interpreted as representing the transition region of the overlying hot coronal loops. However, 17.1 nm images show that similar reticulated structure is present at lower intensity levels everywhere on the Sun outside of coronal holes, although its presence in weak-field and internetwork regions is often masked by the overlying fibrils. In the quiet Sun, the moss tends to be clustered around the bases of Fe xii 19.3 nm loops, with continual jet-like ejections being observed along their stalks. Depending in part on the viewing angle, the curved structures surrounding the “holes” in the moss often resemble small, highly dynamic loops with sizes of ∼2–5 Mm. We discuss two different physical interpretations of the moss. First, in line with the traditional view, it may represent the transition region of coronal loops both inside and outside ARs, with heat being conducted downward into the moss from greater heights and the dark holes representing the spaces between the heated footpoints. An alternative interpretation is that the moss consists mainly of small loops that continually undergo magnetic reconnection with the overlying coronal field, with the associated heating rate depending on the local field strength. This scenario is supported by the tendency for the moss to spill over into weak internetwork regions and by the continual jetting activity observed from network flux concentrations.
SN - 0004-637X
SN - 1538-4357
ER -