A pair of spacecraft will fly in formation to create artificial solar eclipses

A pair of spacecraft just launched to create hundreds of artificial solar eclipses in orbit.

The European Space Agency’s mission, called Proba-3, will allow scientists to “see an eclipse on demand” as one satellite blocks the other’s view of the sun, says mission scientist and solar physicist Andrei Zhukov of Royal Observatory of Belgium in Brussels. .

This, in turn, will allow researchers to easily study the middle part of the corona, the uppermost region of the sun’s atmosphere. Scientists suspect that many of the sun’s most enduring mysteries, from how the solar wind accelerates to why the corona is so much hotter than the sun’s surface, may have solutions in this elusive region. “It’s really a game changer,” says Zhukov.

The mission — launched from India on Dec. 5 at 5:34 a.m. EST — consists of two satellites that will fly together in locked steps as if they were a single rigid structure in space. While in formation, the satellites will stand 144 meters apart to an accuracy of one millimeter.

One satellite, when pointed, will block the sun from another’s view, mimicking a total solar eclipse. The observing spacecraft will then send back high-resolution images of the innermost part of the sun’s diaphanous atmosphere.

Normally, scientists can use satellites to observe the corona right on the sun’s surface in extreme ultraviolet wavelengths of light. Scientists can also construct an artificial eclipse in a telescope by placing a disk called a coronagraph in front of the lens. But light waves bend around the sharp-edged disk in a process called diffraction, distorting the image. So the coronagraph must block a significant area around the sun, limiting how close such observations can get to the star itself.

The region in between, at distances from the surface of about one to three times the Sun’s radius of about 700,000 kilometers, can only be observed during a total solar eclipse. (SN: 4/8/24). “But they are very rare,” says Zhukov. The alignment of the sun, moon, and earth occurs approximately once a year, can only be seen from specific points on the planet, and lasts only a few minutes.

Proba-3 will create eclipses on demand that will last six hours. This long duration will allow scientists to see how the corona moves and changes over time.

And the large distance between the two spacecraft means that diffraction is less of an issue. The further away the occulter is, the more scattered light can spread before reaching the observer. It’s essentially casting a sharper shadow, says physicist Amir Caspi of the Southwest Research Institute in Boulder, Colo.

“The most interesting thing about Proba-3 is that they will place the occulter much farther than you could reasonably do with a single spacecraft,” says Caspi. “That means you can make the occulter exactly the right size and you can see closer to the solar surface.”

Staying in the eclipse formation all the time would use a lot of fuel, so the satellites will spend most of their time flying freely. But scientists still expect more than 1,000 eclipses during the full two-year mission.

Flying satellites of precise formation will also be useful for future missions. Such a system, for example, could link several telescopes together to act as one, effectively creating a telescope far wider than anything that could be launched from Earth.

Caspi thinks the observations from Proba-3, in combination with other spacecraft, will set the stage for the next decade of solar science.

“It’s a very creative use of formations flying in space to achieve something that would be almost impossible, if not actually impossible, to do with a single spacecraft,” says Caspi. “It opens up this new discovery space of observations that have been inaccessible until now.”