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NASA to Chase Eclipse with a Pair of WB-57s at 50,000 Feet
Posted by Guy Pirro on 8/11/2017 4:39 PM

This is a composite photo of a pair of NASA WB-57 aircraft during the 2015 total solar eclipse at the Faroe Islands. For the upcoming total solar eclipse in the USA, a team led by Southwest Research Institute will observe the solar corona using stabilized telescopes aboard two of these WB-57 research aircraft. This vantage point will provide distinct advantages over ground based observations. Images of the Sun will primarily be captured at visible light wavelengths, specifically the green light given off by highly ionized iron as it is super-heated by the Corona. This light is best for showing the fine structures in the Sun's outer atmosphere. The images will complement those taken by space based telescopes, like NASA's Solar Dynamics Observatory, which creates images primarily in ultraviolet light. (Image Credit: NASA, Faroe Islands, Southwest Research Institute - SwRI)


A team led by Southwest Research Institute (SwRI) will use airborne telescopes aboard NASA research aircraft to study the solar corona and Mercury's surface during next week's total solar eclipse. The August 21 observations will provide the clearest images to date of the Sun's outer atmosphere and attempt the first-ever thermal images of surface temperature variations on Mercury.

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 corona is heated to millions of degrees, yet the lower atmospheric layers like the photosphere -- the visible surface of the Sun -- are only heated to a few thousand degrees. Scientists aren't sure how this inversion happens. One theory proposes that magnetic waves called Alfven waves steadily convey energy into the Sun's outer atmosphere, where it is then dissipated as heat. Alternatively, micro explosions, termed nano-flares -- too small and frequent to detect individually, but with a large collective effect -- might release heat into the corona.

"By looking for high-speed motion in the solar corona, we hope to understand what makes it so hot. It's millions of degrees Celsius, hundreds of times hotter than the visible surface below," said Dr. Amir Caspi, principal investigator of the project and a senior research scientist in SwRI's Boulder, Colorado, office. "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."

Why is the Sun's outer atmosphere so much hotter than its surface? Perhaps the Sun's magnetic field carries energy into the corona and converts it into heat. Or perhaps nano-flares or nano-jets -- explosions or eruptions too small and numerous to see individually-- are constantly releasing small amounts of energy that combine to heat the entire corona.

Due to technological limitations, no one has yet directly seen nano-flares, but the high resolution and high speed images to be taken from the WB-57 jets might reveal their effects on the corona. The high definition pictures, captured 30 times per second, will be analyzed for wave motion in the corona to see if waves move towards or away from the surface of the Sun, and with what strengths and sizes.

"We see the evidence of nano-flare heating, but we don't know where they occur," Caspi said. "If they occur higher up in the corona, we might expect to see waves moving downwards, as the little explosions occur and collectively reconfigure the magnetic fields."

In this way, nano-flares may also be the missing link responsible for untangling the chaotic mess of magnetic field lines on the surface of the Sun, explaining why the corona has neat loops and smooth fans of magnetic fields. The direction and nature of the waves observed will also help distinguish between competing models of coronal heating.

For most viewers, the August 21, 2017 total solar eclipse will last less than two and half minutes. But for one team of NASA funded scientists, the eclipse will last over seven minutes. Their secret? Following the shadow of the Moon in two retrofitted WB-57 jet planes. Amir Caspi of the Southwest Research Institute in Boulder, Colorado, and his team will use two of NASA's WB-57 research jets to chase the darkness across America on August 21st. Taking observations from twin telescopes mounted on the noses of the planes, Caspi will capture the clearest images of the Sun's outer atmosphere (the Corona) and the first ever thermal images of Mercury, revealing how temperature varies across the planet's surface. (Video Credit: NASA's Goddard Space Flight Center)

The team will use high speed, high definition video of the corona to look for fast, coherent motions that could help solve this puzzle. 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 Dr. Craig DeForest, a co-investigator also from 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 infrared cameras at 50,000 feet. This high altitude provides distinct advantages over ground based observations.

"Being above the weather guarantees perfect observing conditions, while being above more than 90 percent of Earth's atmosphere gives us much better image quality than on the ground," said another SwRI co-investigator, Dr. Constantine Tsang. "This mobile platform also allows us to chase the eclipse shadow, giving us over 7 minutes of totality between the two planes, compared to just 2 minutes and 40 seconds for a stationary observer on the ground."

The two planes, launching from Ellington Field near NASA's Johnson Space Center in Houston will observe the total eclipse for about three and a half minutes each as they fly over Missouri, Illinois and Tennessee. By flying high in the stratosphere, observations taken with onboard telescopes will avoid looking through the majority of Earth's atmosphere, greatly improving image quality. At the planes' cruising altitude of 50,000 feet, the sky is 20 to 30 times darker than as seen from the ground, and there is much less atmospheric turbulence, allowing fine structures and motions in the Sun's corona to be visible.

Images of the Sun will primarily be captured at visible light wavelengths, specifically the green light given off by highly ionized iron, superheated by the corona. This light is best for showing the fine structures in the Sun's outer atmosphere. These images are complementary to space based telescopes, like NASA's Solar Dynamics Observatory, which takes images primarily in ultraviolet light and does not have the capacity for the high speed imagery that can be captured aboard the WB-57F.

These are the first astronomical observations for the WB-57s. Southern Research, which is located in Birmingham, Alabama, built the Airborne Imaging and Recording Systems onboard and is working with the scientific team to upgrade its DyNAMITE telescopes on both planes with solar filters and improved data recorders.

"This airborne platform also provides us with higher quality, higher speed images than are achievable from current or previous space borne instruments," said Caspi. "It highlights the potential of the WB-57 platform for future astronomical 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.

Observations of Mercury will be taken a half hour before and after totality, when the sky is still relatively dark. These images, taken in the infrared, will be the first attempt to map the variation of temperature across the surface of the planet.

Mercury rotates much slower than Earth -- one Mercurial day is approximately 59 Earth days -- so the night side cools to a few hundred degrees below zero while the dayside bakes at 800 degrees Farenheit. The images will show how quickly the surface cools, allowing scientists to know what the soil is made of and how dense it is. These results will give scientists insight into how Mercury and other rocky planets may have formed.

"We plan to measure Mercury in the infrared, in near darkness, and through very little atmosphere," Tsang said. 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 images of the corona will also allow the team to search for a hypothesized family of asteroids called Vulcanoids. Its thought these objects orbit between the Sun and Mercury, and are leftover from the formation of the solar system. If discovered, Vulcanoids could change what scientists understand about planet formation.

The SwRI led team includes scientists from the University of Colorado, the National Center for Atmospheric Research High Altitude Observatory, and the Smithsonian Astrophysical Observatory, as well as international colleagues at Trinity College Dublin in Ireland and the Royal Observatory of Belgium. The team will make its data available to the public after the event. The team's work will also be featured in two documentaries to air on eclipse day and in the fall of 2017.

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