LONDON-The European Cheops space telescope has launched to study planets outside our Solar System.

The observatory will follow up the discoveries of previous missions, endeavouring to reveal fresh insights on the nature of distant worlds: What are they made of? How did they form? And how have they changed through time?

Cheops (short for CHaracterisingExOPlanet Satellite) is a joint endeavour of 11 member states of the European Space Agency (Esa), with Switzerland in the lead.

What will Cheops do?

The University of Bern, together with the University of Geneva, has provided a powerful photometer for the telescope.

The instrument will measure the tiny changes in light when a world passes in front of its host star.

This event, referred to as a transit, will betray a precise diameter for the planet because the changes in light are proportional to the surface of the world. When that information is combined with data about the mass of the object - obtained through other means - it will be possible for scientists to deduce a density.

“From that we can say something about the planet’s composition and internal structure,” said Esa project scientist Dr Kate Isaak. “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,” she told BBC News.

What’s significant about this mission?

Some 4,500 planets have been discovered since the late 1990s using a variety of techniques. But there is a feeling now that the science has to move beyond just detection; beyond just counting planets. We need to profile the objects in a more sophisticated way. Do they have atmospheres and how thick are they? What kind of clouds? Do they possess oceans on their surface? Do they have rings and moons? Cheops ought to be able to address such questions just from looking for these tiny dips in light during a transit.

The mission has been given a list of 400-500 targets to look at over the next 3.5 years. Most of these worlds will be in the size range between Earth and Neptune, sometimes called “super Earths”. From all the exoplanet surveys conducted to date, this grouping would seem to dominate the statistics.