European Space Agency picks Plato planet-hunting mission

A telescope to find rocky worlds around other stars has been selected for launch by the European Space Agency's (Esa) Science Policy Committee.

Known as Plato, the mission should launch on a Soyuz rocket in 2024.

The observatory concept was chosen following several years of assessment in competition with other ideas.

It is expected to cost Esa just over 600 million euros, although hardware contributions from member states will take this closer to a billion (£800m).

Astronomers have so far found over 1,000 planets beyond our Solar System, but none as yet has been shown to be truly Earth-like in terms of its size and distance from a Sun similar to our own.

The PLAnetary Transits and Oscillations of stars mission will look to change that.

It will be tuned specifically to seek out rocky worlds orbiting in the "habitable zone" - the region around a star where water can keep a liquid state.

"Plato will be our first attempt to find nearby habitable planets around Sun-like stars that we can actually examine in sufficient detail to look for life," said Dr Don Pollacco, the University of Warwick researcher who leads the Plato Science Consortium.

"Nearly all the small transiting planets discovered so far have been beyond our technology to characterise. Plato will be a game-changer, allowing many Earth-like planets to be detected and confirmed and their atmospheres examined for signs of life.

"Plato planets will allow us to develop and test theories of planet evolution, understanding the type of small planets in the Universe and the real frequency of Earth-like planets," he told BBC News.

Plato is not really one telescope but rather a suite of 34 telescopes mounted on a single satellite.

The intention is for this array to sweep about half the sky, to investigate some of its brightest and nearest stars.

The observatory will monitor these stars for the tell-tale tiny dips in light that occur when planets move across their faces.

An important part of this investigation will be to perform an intricate study of the host stars themselves, using their pulsations to probe their structure and properties.

Such observations, referred to as asteroseismology, would provide key, complementary information for the proper characterisation of the rocky worlds.

The mission will be led by Dr Heike Rauer at DLR, the German space agency.

The key British hardware contribution will be the camera system that sits behind the telescope suite.

This will incorporate 136 charge-coupled devices (CCDs) produced by the e2v company in Chelmsford, Essex. Just under a metre square and having 2.5 billion pixels, the CCD system will be the biggest ever flown in space.

It seems certain also that the British arm of Airbus Defence and Space (formerly Astrium) will endeavour to lead the construction of the satellite.

Plato should prove to be a good fit with other next-generation astronomical facilities.

These will include the ground-based European Extremely Large Telescope (E-ELT), which will have a primary mirror some 39m in diameter. To be built in Chile, this giant should be operating by 2024, and will have the power to investigate the atmospheres of the Plato's newly discovered planets.

Plato is the third medium-class launch opportunity to be offered under Esa's so-called Cosmic Vision programme, which defines the organisation's space science priorities.

The first two to be selected were Solar Orbiter, a space telescope to study the Sun, to launch in 2017; and Euclid, a telescope to investigate "dark energy", to fly in 2020.

Esa will now refine the final design of Plato and select the industrial prime contractor.

In addition, the agency's national member states must also agree any contributions they wish to make over and above their mandatory commitments.

Once all this is done, the mission will be formally "adopted" - legal-speak for "final go-ahead". This should happen within the next two years.

The unanimous selection of Plato by the SPC on Wednesday will be immensely pleasing to the team behind the Eddington space telescope - an Esa mission to find distant planets and do asteroseismology that was cancelled due to budget woes in the early 2000s.

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