A new space-based telescope that aims to study planets outside the solar system has been launched by the European Space Agency (ESA).
Cheops (which stands for CHaracterising ExOPlanet Satellite) will initially work through a list of between 400 and 500 planets over the next three and a half years.
Around 4,500 planets have been discovered since the late 1990s, but most have simply been located and identified.
Cheops intends to go much further, by determining some of the important characteristics of its target planets.
2019 Physics Nobel laureate Professor Didier Queloz said that in astronomy, it was common to use a smaller telescope ‘to identify’ and a more powerful one ‘to understand’.
Cheops will attempt to understand the planets it is looking at using a powerful photometer provided by the universities of Bern and Geneva.
This instrument measures the tiny changes in light when the planet passes in front of the star it orbits, allowing them to work out the body’s dimensions.
This can be combined with data on the planet’s mass, obtained through other means, to work out its density.
Cheops’ observations will reveal details of planets’ compositions
ESA project scientist Dr Kate Isaak told BBC News: “From that we can say something about the planet’s composition and internal structure.
‘And by measuring this for many different planets orbiting different types of stars, those close in and far out – we can also say something about the formation and evolution of planets.’
Despite the power of the photometer, collecting and interpreting readings will still present a challenge.
When a planet the approximate size of Jupiter passes in front of a star such as the Sun, the loss in readable light observed by Cheops could be about 1% of the total signal.
For a smaller planet the size of the Earth, the drop will be a hundred times smaller, at 0.01% of the total observable signal.
Professor Willy Benz, the Cheops consortium principal investigator, said: ‘The difficulty was in building an optical system that is capable of measuring these minute light changes.
‘To give you an example, when we wanted to test this in the lab we didn’t find a single light source in the world that was stable to this precision to allow us to test our telescope – so we had to build one.’
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