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We will use new data from the High-resolution Coronal Imager (Hi-C) withunprecedented spatial resolution of the solar corona to investigate thestructure of coronal loops down to 0.2 arcsec. During a rocket flight Hi-Cprovided images of the solar corona in a wavelength band around 193 A that isdominated by emission from Fe XII showing plasma at temperatures around 1.5 MK.We analyze part of the Hi-C field-of-view to study the smallest coronal loopsobserved so far and search for the a possible sub-structuring of larger loops.We find tiny 1.5 MK loop-like structures that we interpret as miniature coronalloops. These have length of the coronal segment above the chromosphere of onlyabout 1 Mm and a thickness of less than 200 km. They could be interpreted asthe coronal signature of small flux tubes breaking through the photosphere witha footpoint distance corresponding to the diameter of a cell of granulation. Wefind loops that are longer than 50 Mm to have a diameter of about 2 arcsec or1.5 Mm, consistent with previous observations. However, Hi-C really resolvesthese loops with some 20 pixels across the loop. Even at this greatly improvedspatial resolution the large loops seem to have no visible sub-structure.Instead they show a smooth variation in cross-section. The fact that the largecoronal loops do not show a sub-structure at the spatial scale of 0.1 arcsecper pixel implies that either the densities and temperatures are smoothlyvarying across these loops or poses an upper limit on the diameter of strandsthe loops might be composed of. We estimate that strands that compose the 2arcsec thick loop would have to be thinner than 15 km. The miniature loops wefind for the first time pose a challenge to be properly understood in terms ofmodeling.

Structure of solar coronal loops: from miniature to large-scale