TRACE produced the pictures that changed how people imagine the Sun. Its small ultraviolet telescope resolved coronal loops — the arcs of hot plasma suspended along magnetic field lines — in detail nothing had achieved before, revealing them as thin, braided, constantly shifting strands rather than smooth arches.
Those images made the corona's structure visceral. It became obvious that the solar atmosphere is organised entirely by magnetism, that the loops are heated unevenly along their length, and that the coronal heating problem is a question about small scales rather than large ones.
The mission was deliberately narrow — one instrument, one waveband range, one purpose — and it was launched cheaply as a Small Explorer. Its Sun-synchronous polar orbit gave it months of continuous sunlight without eclipses.
It observed transition-region and coronal structures at the same time as SOHO watched the larger picture, and the two missions were frequently used together — one for context, the other for detail.
It operated from 1998 to 2010 and was superseded by SDO, whose imagers cover the same wavelengths with a larger field and higher cadence. TRACE established the visual vocabulary that SDO inherited, and its images still appear in textbooks.
