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TRACE mission graphic

Transition Region and Coronal Explorer

Phase: Past

Launch Date: April 01, 1998

Mission Project Home Page -

Program(s):Explorers, Heliophysics Explorers, Heliophysics Research

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The objective of the Transition Region and Coronal Explorer (TRACE) satellite was to explore the three-dimensional magnetic structures which emerge through the visible surface of the Sun -- the Photosphere -- and define both the geometry and dynamics of the upper solar atmosphere - the Transition Region and Corona. The magnetic field geometry can be seen in images of solar plasma taken in wavelengths emitted or absorbed by atoms and ions formed in different temperature ranges. The transition from the 6000 degree K Photosphere, where magnetic fields and plasma are in rough equipartition (low beta), to the multi-million degree Corona, where the magnetic fields dominate (high beta), is extremely difficult to model. Many of the physical process that occur here -- plasma confinement, reconnection, wave propagation, plasma heating -- arise throughout space physics and astrophysics. And to date, no images have ever been collected that show the required temperature range nearly simultaneously with both high spatial and temporal resolution.

This colorized picture is a mosaic of ultraviolet images from the orbiting TRACE satellite sensitive to light emitted by highly charged iron atoms. Growing in number, the intricate structures visible are the Sun's hot active regions with temperatures over a million degrees Fahrenheit and their associated magnetic loops.

Image credit: TRACE Team, NASA

The TRACE data provided quantitative observational constraints on the models and thus stimulate real advances in our understanding of the transition from low to high beta plasma. The solar atmosphere is constantly evolving because the magnetic fields which dominate the Corona are continuously being displaced by the convective motions in the outer layers of the Sun just below the Photosphere.

A major objective of the TRACE investigation was to explore the relation between diffusion of the surface magnetic fields and the changes in heating and structure throughout the Transition Region and Corona. The simultaneous movies of the 6000 to 10,000,000 degree K volume of the solar atmosphere allowed us to determine the rate of change of the magnetic topology and the nature of the local restructuring and reconnection processes.

Occasionally new magnetic flux emerges through the solar surface and organizes into local concentrations the largest of which are sunspots. The emergence of new flux has profound effects on the overlying atmosphere and often triggers a variety of phenomena which release significant amounts of energy and which can result in major restructuring of the Corona, the interplanetary medium, and the Earth's magnetosphere. Therefore, TRACE observed continuously for an extended period to study not only the "quiet" solar atmosphere but also the more episodic active Sun.