Scientists prepare to study solar eclipse with high-altitude aircraft and solar orbiting probes

For the millions of people across North America who will experience a total solar eclipse on April 8, it will be a spectacular spectacle – a chance to see the moon completely obscuring the face of the sun.

But for scientists, it’s a rare opportunity to study Earth, the moon and the sun “in completely different ways than we normally do,” said NASA deputy administrator Pam Melroy.

One of the agency’s main priorities will be to look at the sun’s outer atmosphere, or corona, which is not normally visible because the star is too bright. During a total solar eclipse, the corona appears faintly swirling around a bright star when the moon blocks light from the sun’s surface.

“There are things happening with the corona that we don’t fully understand, and the eclipse gives us a unique opportunity to collect data that could provide insights into the future of our star,” Melroy said at a briefing last week.

Scientists are interested in the corona because it plays a central role in transferring heat and energy into the solar wind, the continuous stream of charged particles released from the sun’s outer atmosphere. The solar wind ebbs and flows, occasionally shooting high-powered solar flares into space. These can hit the Earth with electromagnetic radiation, which can cause radio blackouts and knock out power grids.

Amir Caspi, a solar astrophysicist at the Southwest Research Institute in Boulder, Colorado, has installed an instrument in the nose of the WB-57 aircraft that will study the sun’s atmosphere as the plane chases the eclipse.

It’s a golden opportunity, he said, since even the special telescopes that can block out starlight, called coronagraphs, have limitations.

“A total solar eclipse is like nature’s perfect coronagraph,” he said. “The moon comes between us and the sun, and it’s just the right size in the sky to block out the sun’s disk but not much more.”

Caspi will focus on trying to understand the origin of the solar wind. It also hopes to gather clues about a long-standing mystery: why the corona is millions of degrees hotter than the surface of the sun.

He pioneered this method of imaging the sun’s corona in 2017, during the last total solar eclipse to cross the continental US

“We didn’t know what we were going to get,” he said. “He was picking a nail for quite some time, and then we got some great data. I could see it coming down from the live satellite feed.”

The WB-57 plane can fly at an altitude of 60,000 feet, well above any clouds and high enough that the Earth’s atmosphere will not affect the observations as much.

Many researchers plan to collect data about the sun’s atmosphere from other vantage points during the eclipse, including from space.

Several spacecraft, including NASA’s Parker Solar Probe, will train their eyes on the sun during the celestial event. The probe was launched in 2018, so it was not available to study the 2017 solar eclipse.

In 2021, the Parker probe became the first spacecraft to fly through the corona, and it has since flown more than a dozen close approaches to the sun. Due to the timing of its orbit, the probe will not be in close proximity on April 8. But it will be close enough to the sun to measure and image the solar wind as the charged particles stream by, according to Parker’s Nour Raouafi. Solar Probe project scientist and astrophysicist at the Johns Hopkins Applied Physics Laboratory.

In addition, a European Space Agency spacecraft, called Solar Orbiter, will be orbiting almost directly above the Parker Solar Probe at the time of the eclipse. Together, the observatories will deploy a team to obtain data about the sun’s atmosphere and solar wind.

“It’s one of the rare occasions that these two spacecraft come so close to each other,” Raouafi said. “So, we’re going to have a lot of synergies between them, between all the observing that we’ll do during the eclipse from Earth, which is completely, completely unprecedented.”

The sun is climbing toward a peak in its roughly 11-year cycle of activity, expected in 2025. That means the Parker Solar Probe will have a front-row seat to any eruption from the sun.

There are no guarantees that such outbursts will occur during the eclipse, but Raouafi said measurements of the solar wind from space will still be critical to understanding the effects of solar activity on Earth.

“These are the drivers of space weather, and the probe is probably the best tool we have out there, the best spacecraft mission we have there, to help us understand that,” he said. “And the way to do it? We hope the sun will put on the biggest show it can produce.”

Even for nonscientists, the temporary hold of darkness on evening skies along the so-called path of totality will be an unusual experience.

“I remember the first time I learned that it’s a very rare thing – that our moon just happens to be the right size and distance to create this effect here on Earth,” said Melroy. “It really is a miracle for our universe.”

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