In this illustration, the two spacecraft of Proba-3 fly in precise formation about about 500 feet apart to form an external coronagraph in space. One spacecraft eclipses the sun to allow the second to study the invisible solar corona.
ESA-P. Carril @ESA/European Space Agency
A pair of spacecraft have been launched on a mission to help scientists get a better understanding of the sun by creating artificial solar eclipses.
Proba-3, which includes two satellites, launched earlier this month from India by the European Space Agency. The mission will attempt a scientific feat by being the first to use a two-spacecraft setup to observe the corona, the sun’s outer atmosphere.
The eclipses created by Proba-3 will not cast shadows that can be seen on Earth, the ESA says. But if successful, the ESA and astronomers hope the mission will answer several questions, including why the corona is hotter than the sun itself. The corona can reach 2 million degrees Fahrenheit, while the surface is 10,000 degrees, according to NASA.
“The ability of this mission to observe the corona so close to the sun for extended periods is an extraordinary opportunity,” Talwinder Singh, assistant professor of physics and astronomy at Georgia State University, tells NPR. “If successful, it will pave the way for similar missions that provide continuous, high-resolution observations of the sun’s corona.”
A better way to examine the sun
It’s not the first time scientists have used artificial eclipses to study the sun, but some astronomers say this mission could achieve something the earlier missions weren’t able to do.
Studying the sun’s corona is extremely difficult because it is hidden by light from the star’s surface, according to NASA. And one of the best ways to study the corona is during a total solar eclipse, when the moon passes between Earth and the sun and blocks the sun. During a total solar eclipse, the corona is visible. But total solar eclipses are rare, with the next one taking place in August 2026.
Several missions have studied the sun and created artificial eclipses, including the ESA and NASA’s Solar Terrestrial Relations Observatory (STEREO) mission that used a coronagraph to block the sun. But because the sun’s surface is so bright, the instruments in those missions only block much of the lower part of the corona to reduce the amount of scattered light, according to Kathy Reeves, senior astrophysicist at the Center for Astrophysics Harvard & Smithsonian.
“What is interesting about the Proba-3 instrument is that the occulter is actually on a different spacecraft, so it can be quite far away, and using this technique, the instrument can block the sun’s disk more precisely,” Reeves says.
The Proba-3 mission, which will fly in an elliptical orbit ranging from 372 miles to 37,000 miles above Earth’s surface, is also groundbreaking because it uses two separate spacecraft — one carrying the occulter disk and the other the imaging camera, when previous missions have only used one spacecraft, according to Talwinder Singh, assistant professor of physics & astronomy at Georgia State University.
The moon covers the sun as it creates a total eclipse on Aug. 21, 2017, in Cerulean, Ky. The corona, the outer atmosphere of the sun, is visible.
Timothy D. Easley/AP
“Similar instruments, called coronagraphs, have been used in the past. However, traditional coronagraphs place the occulter disk on the same spacecraft as the imaging camera. This design has limitations, such as light diffraction, which restricts how close to the sun we can observe,” Singh says.
During the Proba-3 mission, one satellite, the Occulter, will line up with the sun and cast a shadow onto the other spacecraft, the Coronagraph. The corona will be visible, just like during an actual eclipse, and the Coronagraph will take a photo of the inner part of the corona, according to the ESA.
The instruments will be about 500 feet apart, longer than the length of an American football field, which will allow scientists to get a closer view of the corona. It will also allow scientists more time to study the sun, at least six hours in every 20-hour orbit, compared to an actual solar eclipse than is witnessed from Earth.
“Natural eclipses only happen once or twice per year, sometimes they happen in inconvenient places, like over the ocean, and they are only a few minutes long,” Reeves says. “This mission is really neat because it will extend the amount of time that scientists can study the Sun’s middle corona from minutes to hours.”
The mission is not going to directly impact the Earth and the fake solar eclipses will not be cast down on earth, Singh and Reeves say.
The first results from the mission will be available around four months after the spacecraft separate and fly in sync in early 2025, according to the ESA.
