A team led by Southwest Research Institute (SwRI) will use airborne telescopes aboard a NASA research aircraft to study the solar corona and Mercury's surface during this summer's total solar eclipse. Total solar eclipses are unique opportunities for scientists to study the hot atmosphere above the sun's visible surface. The faint light from the corona is usually overpowered by intense emissions from the sun itself. During a total eclipse, however, the moon blocks the glare from the bright solar disk and darkens the sky, allowing the weaker coronal emissions to be observed. The August 21 observations will provide the clearest images to date of the sun's outer atmosphere and the team will attempt the first-ever thermal images of surface temperature variations on Mercury. "By looking for high-speed motion in the solar corona, we hope to understand what makes it so hot,” said Amir Caspi, principal investigator of the project and a senior research scientist at SwRI's Boulder facility. “It's millions of degrees Celsius, hundreds of times hotter than the visible surface below. In addition, the corona is one of the major sources of electromagnetic storms here at Earth. These phenomena damage satellites, cause power grid blackouts and disrupt communication and GPS signals, so it's important to better understand them." The team will use high-speed, high-definition video of the corona to look for fast, coherent motions. The project may also shed light on another question: why the magnetic structures in the corona are relatively smooth and stable. "The magnetic field forms well-organized loops and arcades in the lower corona, as well as large, fan-shaped structures extending out to many solar radii," said Craig DeForest, a co-investigator at SwRI's Boulder office. "These structures are constantly being churned and tangled by the motion of the solar surface itself. So why does the corona always appear well organized, like a recently coiffed head of hair, and not snarled or matted?" From two of NASA's WB-57 research aircraft, the team will observe the corona during the eclipse using stabilized telescopes with sensitive, high-speed, visible-light and IR cameras at 50,000 ft. This high altitude provides distinct advantages over ground-based observations. Eclipse observations also give the team a unique opportunity to study Mercury, the planet closest to the sun. Mercury is difficult to observe because it is usually washed out by the bright daytime sky, or distorted by the atmosphere near the horizon at twilight. "We plan to measure Mercury in the infrared, in near darkness and through very little atmosphere," said Constantine Tsang, SwRI co-investigator. “Scientists hope to use infrared measurements to calculate surface temperatures over the planet's entire night side. How the temperature changes across the surface gives us information about the thermophysical properties of Mercury's soil, down to depths of about a few centimeters, something that has never been measured before." The SwRI-led team includes scientists from the University of Colorado, the National Center for Atmospheric Research, the High Altitude Observatory and the Smithsonian Astrophysical Observatory, as well as international colleagues at Trinity College Dublin and the Royal Observatory of Belgium.