The sun’s ghostly corona – an aura of plasma in its outer atmosphere a million times fainter than the sun itself – is normally hidden from view. But every so often, astronomers are treated to a solar eclipse, which blocks the sun’s light and brings its corona to life.
The problem is that solar eclipses take place every 18 months or so and are only viewable at certain points on Earth. So the European Space Agency has planned a mission to induce eclipses on demand.
The Proba-3 mission comprises two satellites: an “occulter” satellite which will fly 150 metres ahead of a second “coronagraph” satellite. The occulter satellite will cast a precise shadow onto the coronagraph, like the moon does during a solar eclipse.
“The coronagraph idea was conceived by astronomer Bernard Lyot in the 1930s – and since then has been developed and has been incorporated into both Earth-based and space telescopes,” explains Proba-3 payload manager Damien Galano.
“But because of the wave nature of light, even within the cone of shadow cast by the occulter, some light still spills around the occulter edges, a phenomenon called ‘diffraction’.
“To minimise this unwanted light, the coronagraph can be positioned closer to the occulter – and therefore deeper into the shadow cone.”
The satellite pair will whiz around Earth in an elliptical orbit, coming as close as 600 kilometres and zooming out as far as 60,000 kilometres, or a seventh the distance to the moon.
It’s planned to launch in 2019.