Artificial solar eclipse created by 'driverless' spacecraft in world first

Two "driverless" spacecraft have flown in perfect formation to create a small artificial solar eclipse and "achieve what no other mission has before", the European Space Agency (ESA) has said.

The synchronised flight orbiting Earth allowed one of the satellites to cast an 8cm-wide shadow onto its sister craft, flying 150 metres away, by blocking its view from space of the sun's surface.

The technique helped the space agency to capture detailed images of the sun's fiery outer atmosphere, called the corona.

Scientists increasingly need to study the corona, but find it hard to do so without an eclipse because the sun's surface is one million times brighter.

Image: A combined picture of the outer corona (in red), the inner corona (in green) and the sun's disc (in yellow). Pic: ESA/NASA

Solar wind, the flow of matter from the sun to outer space, and coronal mass ejections, the eruptions of plasma from the sun, can both interfere with modern technology like satellites – as well as cause displays of the Northern and Southern Lights.

It is hoped that studying the corona more closely will help scientists better understand solar weather, as well as answer questions about the sun itself.

Image: A loop is seen on the left side of the corona, which generally appears after a solar flare. Pic: ESA/NASA

The images from the Proba-3 mission were taken in March but have only been released by the space agency this week.

"We can create our eclipse once every 19.6-hour orbit, while total solar eclipses only occur naturally around once, very rarely twice a year," said Andrei Zhukov from the Royal Observatory of Belgium.

"On top of that, natural total eclipses only last a few minutes, while Proba-3 can hold its artificial eclipse for up to six hours."

Image: An illustration demonstrating the two satellites lining up. Pic: ESA-P. Carril

The two satellites are able to align with the sun so that the 1.4-metre disc carried by one of the spacecraft, the Occulter, covers the bright disc of the sun and casts a shadow.

The other spacecraft, the Coronagraph, then takes a series of photographs with different exposure times.

Image: The solar corona is seen similarly to how a human eye would see it during an eclipse through a green filter. Pic: ESA/NASA

The satellites flew within 150 metres of each other, with a precision "equal to the thickness of the average fingernail", according to the ESA.

Rather than relying on human drivers, who would have an "uncomfortable" delay of a fifth of a second while steering, the spacecraft autonomously lined themselves up with the sun in a manner "akin to driverless cars", the space agency said.

When the spacecraft blasted off in December last year, they had enough fuel to keep going for around two years.

After five years, it is expected they will burn up in the Earth's atmosphere.