ESA’s Proba-3 satellite will create its own solar eclipses in 2019

22 Aug 2016

A new European Space Agency (ESA) satellite being readied for launch in 2019 intends to create its own solar eclipses, albeit on a much smaller scale than the real thing, to help us understand more about the sun’s corona.

While astronomers and the public alike are fascinated by the appearance of solar eclipses in our skies every 18 months or so, ESA scientists are now looking to study them in greater detail with the help of its new double-satellite, Proba-3.

The two separate craft will combine to create solar eclipses that last for hours on end, allowing ESA researchers to analyse the sun’s outer atmosphere, known as its corona, in unprecedented detail.

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In order for astronomers to measure the corona, the sun needs to be entirely blocked out – just like during a solar eclipse – as the corona is around 1m-times fainter than the sun itself.

With plans to launch the craft in 2019, Proba-3 will become the first precision formation-flying astronomical mission ever conducted.

In explaining how such a pairing of satellites will work, the first craft – known as the ‘occulter’ satellite – will fly 150m in front of the second ‘coronograph’ satellite, or ASPIICS, to give it its scientific name.

This latter satellite will then cast a precise shadow on the occulter satellite, revealing the solar corona down to a precise measurement of 1.2 solar radii.

Coronograph satellites

Proba-3 flying in formation creating a solar eclipse. Image via ESA–D. Galeno

Could be used to monitor exoplanets

The ASPIICS instrument will also contain a smaller, secondary occulter disk, to cut down on diffracted light that could spill around the main occulter’s edges.

This coronagraph concept was first conceived by astronomer Bernard Lyot in the 1930s and has since gone on to be used in Earth-based telescopes, but a space-based telescope would offer greater insight into the phenomenon.

“Precision is all,” said Damien Galano, Proba-3’s payload manager.

“The aperture of the ASPIICS instrument measures 50mm in diameter, and for corona observation performance it should remain as much as possible in the centre of the shadow, which is about 70mm across at 150 metres.”

Galano went on to say that this same approach to measuring objects in space could be used to examine distant exoplanets.

“It’s a similar challenge, the main difference being that the star in question is a point source of light rather than the extended source that our sun is,” he said.

“So it could be that formation-flown external occulters become versatile scientific tools, opening many new vistas in astronomy.”

Colm Gorey was a senior journalist with Silicon Republic