Great American Eclipse: Why NASA is Chasing the Total Solar Eclipse with Jet Planes

total solar eclipse
A total solar eclipse over Japan in 2009. National Astronomical Observatory of Japan via Getty Images

NASA is preparing to study the total solar eclipse on Monday by chasing the path of totality with jet planes. By doing so, the space agency should be able to capture the clearest ever image of the sun's outer atmosphere—its corona.

The corona is like a fiery shell of plasma that surrounds the sun, reaching temperatures of over 1 million degrees Celsius. It is the place where solar winds and coronal mass ejections come from, both of which have the potential to affect Earth. A large CME, for example, could knock out communications satellites and power grids, with one U.S. government report indicating it could cause up to $2 trillion worth of damage.

However, our understanding of the sun's corona is limited. Compared with the sun, it is very dim, so when scientists try to look at it, it is obscured by the brightness of the sun's surface. During a solar eclipse, however, this all changes. With the sun's light blocked out, researches can look at the corona in far more detail.

Total solar eclipse corona
This National Solar Observatory image shows a model of the sun's corona during the August 21 total solar eclipse, based on measurements taken one solar rotation (or 27.2753 Earth days) before the event. National Solar Observatory

To take advantage of the forthcoming eclipse, which will pass across the entire U.S., from the Pacific to the Atlantic, NASA plans to follow the event with superfast planes flying high in the stratosphere and cruising at an altitude of 50,000 feet.

The two WB-57F research jets have been modified so that telescopes are mounted on their noses. These telescopes will be used to take high-definition pictures of the corona 30 times per second. Because of the high altitude, the sky will be 20 to 30 times darker than it is on the ground. There will also be less atmospheric turbulence. Combined, this should provide scientists with the clearest-ever view of the corona taken to date.

Each plane will track the eclipse for three and a half minutes, giving a total observation time of seven minutes. From a static point on the surface of Earth, the maximum observation time is just two and a half minutes.

"These could well turn out to be the best-ever observations of high-frequency phenomena in the corona," Dan Seaton, co-investigator of the project and a researcher at the University of Colorado, said in a statement. "Extending the observing time and going to a very high altitude might allow us to see a few events or track waves that would be essentially invisible in just two minutes of observations from the ground."

One of the mysteries of the sun's corona scientists hope to solve is why it is so much hotter than the sun's surface, which is just a few thousand degrees Celsius. One suggestion is that magnetic waves move energy from the surface to the outer atmosphere, where it is released as heat. Another theory is that tiny explosions, or nanoflares, are constantly taking place on the sun's surface and releasing heat into the corona.

An eruption of solar material from the sun, also known as a coronal mass ejection. NASA

"We see the evidence of nanoflare heating, but we don't know where they occur," says Amir Caspi, whose team from the Southwest Research Institute in Boulder, Colorado, will be flying in the jets. "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."

As well as looking at the corona, the jets will be used to observe Mercury, taking the first-ever thermal images of the planet to see how temperature varies across its surface. Because Mercury spins far slower than Earth, the side facing the sun ends up reaching around 420 degrees Celsius, while temperatures on the dark side plummet far below zero. Understanding how fast the surface cools down at night will help researchers work out what the soil is made from and how dense it is—potentially shedding light on how it and the other rocky planets formed.

The path of totality will pass through 10 states: Oregon, Idaho, Wyoming, Nebraska, Missouri, Illinois, Kentucky, Tennessee, North Carolina and South Carolina. Read our guide on when to watch the total solar eclipse in each state here.