Solar Eclipse-Chasing Jets Aim to Solve Mystery of Sun's Corona

The researchers will use cameras installed on two of NASA's WB-57 research jets to make high-resolution moving observations of the sun's corona — the ethereal streamers of glowing gas in the sun's outermost atmosphere that only become visible during a solar eclipse.

While observers on the ground will experience up to two-and-a-half minutes of totality (when the moon completely obscures the sun), the NASA-funded team led by Amir Caspi, a solar astrophysicist at the Southwest Research Institute in Boulder, Colorado, will use the jets to stretch the period of totality to more than 7 minutes, allowing unprecedented observations of the solar corona. [In Photos: Eclipse-Chasing Jets Aim to Get Best-Ever View of Sun's Corona]

Even being a passenger on the NASA jets requires special training, so the astrophysicists won't get to fly with the instruments. But, they'll keep track of their experiment through a live satellite feed of the images as the jets chase the moon's shadow over Missouri, Illinois and Tennessee at the height of the total solar eclipse. The live feed will also be made available to the public online.

The moon's shadow moves too fast for even the jets to keep up, so the pilots will fly in a carefully calculated formation that will maximize the time of totality, with the second jet picking up the chase just a few seconds before totality for the first jet comes to an end, according to the researchers.

"Even though they're 100 kilometers [62 miles] apart and flying at about 750 kilometers an hour [470 miles per hour], they will have to time their flight well enough to be within about 10 seconds of the position they need to be," Caspi told Live Science.

Hotter than the sun

The high-resolution images captured by the jets during the eclipse will give the researchers a unique moving view of the sun's corona. They hope it will shed light on the main mystery of the corona: Why is it so much hotter than the surface of the sun itself?

"The solar corona is at a temperature of millions of degrees, and the visible surface of the sun — the photosphere — is only a few thousand degrees," Caspi said. "This kind of temperature inversion is unusual. If thermodynamics worked in the classical sense that we are used to, then you wouldn't get this kind of inversion, and the temperature would fall off as you go higher."

Caspi and his colleagues hope their observations will reveal very fine dynamic features in the solar corona, perhaps in the form of ripples or waves, that could reveal processes in the sun's magnetic field that are thought to keep the thin corona so much hotter than the solar surface.

A second major aim is to search for an explanation for the large visible structures in the corona, Caspi said.

"When you look at the corona, you see these very well-structured loops, arcades, fans and streamers," he said. "The thing is, that they are very smooth and well-organized, and it looks like a freshly combed head of hair."

But the magnetic fields that shape the corona originate in the very chaotic surface of the sun, which would be expected to twist the smooth structures of the corona into a tangled mat, Caspi said.

But, "all these structures stay stable and very well organized, and so the corona is constantly releasing little bits of complexity in order to stay that well organized," he said, "and we don’t understand how that process happens, either."

High-altitude view

Caspi explained that observing a solar eclipse from an altitude of 50,000 feet (15,200 m) has many advantages over observations from the ground. [2017 Total Solar Eclipse: Everything You Need to Know]

The NASA jets will fly well above any clouds and most of the atmosphere that envelops the earth, guaranteeing perfect weather at a time of year when eclipse watchers on the ground can expect around 50 percent cloud cover, he said.

The thin atmosphere and the position of the sun and moon almost directly overhead will reduce distortion to a minimum, which will allow the telescopes and cameras aboard the aircraft to record very fine details in the structure of the sun's corona, he said.

"We basically get better sensitivity in every respect," Caspi said. "We get better image quality, we get longer observing time, we get less scattered light — so we have higher sensitivity to all the things that we're trying to look at in so many different ways."

NASA's WB-57 research jets started out in the 1960s as B-57 Canberra bombers. The planes were then adapted by the U.S. Air Force for weather monitoring and were used to collect high-atmosphere air samples after suspected nuclear tests, according to NASA.

The jets have since been rebuilt and retrofitted with a suite of sophisticated instruments and sensors, including stabilized high-resolution cameras in the nose of the aircraft that can record visible light andinfrared light at 30 frames per second.

Caspi said the camera system was developed by NASA to monitor the space shuttles during re-entry to the atmosphere, as a precaution in the wake on the space shuttle Colombia disaster in 1986.

The Aug. 21 total solar eclipse will be the first time that the NASA jets and its cameras have been used for astronomy, Caspi said.

"So, apart from just being a really amazing piece of science, we hope that this experiment will showcase the performance and potential of this platform for future astronomical observations," he added.

Closest star

Caspi said the upcoming observations have the potential to shed light on some of the lingering mysteries about our closest star, and give astrophysicists a better understanding of how our solar system formed. The research could even offer scientists a glimpse of how other systems of planets form around distant stars.

"Solar system evolution is partly driven by these winds that come out of the star, and they blow a lot of the dust away from the inner solar system, and so that's one of the reasons why rocky planets form close in and gas giants tend to form farther away," Caspi said.

The eclipse flights will also provide a rare opportunity for researchers to observe the planet Mercury with the telescopes and cameras on the jets, Caspi said. They will also have the opportunity to look for the elusive Vulcanoid asteroids that are theorized to exist between Mercury and the sun.

Caspi explained that the jet cameras would be aimed to observe our solar system's innermost planet, which will become visible in the darkened sky during the eclipse, for about half an hour before and half an hour after totality.

High-resolution images of Mercury taken under infrared light would let planetary scientists study the surface of the planet around the dawn terminator, where Mercury's freezing-cold night gives way to its scorching-hot day, to learn more about the material that makes up the surface.

"The day side of Mercury is roasting-hot at 750 degrees F (400 degrees C), and the night side is freezing-cold at minus 250 degrees F (minus 156 degrees C), but what we don’t know is how long it takes to go from hot to cold."

By using infrared light, the scientists will be able to measure the properties of the planet's soil, not just at the surface, but even a few centimeters below the surface, which could help researchers figure out what it is made of and how dense it is, he added.

"These observations are the first of their kind that we know of, to try to make an infrared heat map of Mercury," Caspi said.

Original article on Live Science.