UK will lead European exoplanet mission

A telescope to study the atmospheres of planets beyond our Solar System will be launched by the European Space Agency in the late 2020s.

The mission, to be known as Ariel, was selected by the organisation's Science Programme Committee on Tuesday.

The venture will be led scientifically from the UK by University College London astrophysicist Giovanna Tinetti.

"In the next decade we will see many, many planets being discovered - thousands, actually," she said.

"All this is amazing, but we want to go beyond that and start to understand the nature of those planets, how they formed, how they evolved, and ultimately to put our Solar System in the bigger picture," the principal investigator told BBC News.

Ariel will use a metre-sized mirror and instrumentation designed to analyse, in visible and infrared light, the chemical make-up of the gases that shroud distant worlds, or exoplanets as they are known.

This information should provide insights on how certain types of planets come to form around particular stars.

Prof Tinetti explained: "We want to sample lots of planets - some that are small like the Earth or very big like Jupiter; and at different temperatures - extremely hot, warm or temperate - around very different types of stars.

"We want to sample all the extremes and the more normal cases, because what we want to try to understand is the 'standard model' for planets, if such a model even exists."

Ariel (Atmospheric Remote-Sensing Infrared Exoplanet Large-survey)

Artwork: The mission will cost on the order of half a billion euros

Ariel is the latest selection in Esa's Medium Class portfolio. To win the launch opportunity in 2028, the proposal had to beat competition from an X-ray telescope (Xipe) and a mission to study energetic particles around the Earth (Thor).

A detailed technical assessment will now be conducted before the Ariel project is formally "adopted" - Esa legal-speak for "final go-ahead". This sign-off, which should happen in the next two years, paves the way for manufacture of the flight hardware.

Ariel is the third exoplanet venture chosen by Esa in recent years.

Prof Tinetti has already been working on the concept for the better part of 10 years

Already coming down the line is a small telescope called Cheops that should go up next year to better measure the size of these far-off worlds; and this will be followed in 2026 by Plato, a telescope that aims to find "true Earths" - planets the same size as our home world that orbit at the same distance from Sun-like stars.

And the Americans, too, have their dedicated planet-hunters, with the newest, the Transiting Exoplanet Survey Satellite (Tess), launching in the next few weeks.

But at some point, the science of exoplanets has to move beyond simply finding and counting objects; their chemical compositions and physical conditions have to be determined.

The telescope that will start to make big inroads into this problem is the James Webb observatory, the successor to Hubble.

Due in orbit next year, it will study planetary atmospheres in exquisite detail with its 6.5m-diameter mirror. But the US space agency-led mission will probably only get to look at perhaps 150-200 exoplanets in its first five years of operation because of all the other demands on its time from astronomers.

Ariel, on the other hand, will have the single quest and that should see it characterising in the region of 500-1,000 planets during its primary years in orbit.

Steady platform

And one aspect that would work in Ariel's favour is the absence of any moving parts in its build, commented Plato team-member Dr Don Pollaco from Warwick University, UK.

"The issue with all of these planet experiments is that the signals you are looking for are so incredibly small that any systematics in the instrument itself will dominate the signal," he explained.

"And the systematics are often associated with bits that move. So the great thing about Ariel is that it is fixed-format - nothing changes," he told BBC News.

Ariel is likely to cost Esa about €460m (£405m) for the spacecraft chassis, the launch vehicle and operations. As is customary for science missions like this, the agency's individual member states pick up the cost of the scientific payload.

The UK will have the technical lead on the project and the instrumentation therefore will be assembled at the Rutherford Appleton Laboratory at Harwell in Oxfordshire.

Dr Graham Turnock, the chief executive of the UK Space Agency, said: "It is thanks to the world-leading skills of our innovative space community that a UK-led consortium has been chosen to take forward the next ESA science mission. This demonstrates what a vital role we continue to play in European collaboration on research in space.

"The Ariel mission is a prime example of the scientific innovation underpinning the wider economy. It relies on the UK's science and engineering expertise, which are at the forefront of the government's Industrial Strategy."

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