Paris (AFP)

The Cheops space telescope is due to leave Earth Wednesday, after a delay in launching the previous day, to reach its observation post for exoplanets and try to climb an additional step in understanding the origin of life.

"The Cheops mission represents a step to better understand the astrophysics of all these strange planets that we have discovered and which have no equivalence in the solar system", explains to AFP Didier Queloz, 2019 Nobel Prize in physics .

Nearly 4,000 exoplanets - orbiting a star other than the Sun - have been detected since the astrophysicist and his colleague Michel Mayor found the very first, 51 Pegasi b, 24 years ago.

Today, it is estimated that there are at least as many planets as stars in the galaxy, or about 100 billion. "We want to go beyond statistics and study them in detail," David Ehrenreich, scientific manager of the Cheops mission led by Switzerland and the European Space Agency (ESA), told AFP.

Not all of course. But Cheops will observe about 500 of them and thus compose "a family photo of the exoplanets", says Günther Hasinger, the director of scientific programs at ESA.

How? By observing exoplanets when they pass in front of their star, creating a mini-eclipse.

By comparing the light emitted by the star before, during and after the transit of the planet, astrophysicists will be able to deduce the size and radius of the planet, with unprecedented precision.

This new data, combined with information collected by ground-based telescopes on the ground, will make it possible to measure density, an essential parameter for determining the composition of the planet. A fundamental criterion to define the probability that a planet can harbor life.

- "emotional stage" -

"The mission will also make it possible to measure the amount of light reflected by these planets. By analyzing this light we can have an idea of ​​the structure either of the atmosphere or of the surface," adds Didier Queloz.

"This is not a question that we will resolve with Cheops, but to understand the origin of life, we must understand the geophysics of these planets", explains Didier Queloz. "It's like having a big staircase, you start with the first step."

"It takes a lot of parameters to make life possible," recalls Günther Hasinger.

The Soyuz medium launcher, of which it is the third launch of the year, should take off on Wednesday at 05.54 am Kourou time (08.54 GMT) from the Guiana Space Center.

It will also carry the Earth observation satellite COSMO-SkyMed Second Generation, for the Italian Space Agency (ASI) and the Italian Ministry of Defense. And three auxiliary charges: Angels, the first nanosatellite funded by CNES and produced entirely by French industry; Eyesat, also funded by CNES; and Ops-Sat, on behalf of ESA.

"The launch is an important moment, an emotional stage, but the magic moment for us will be when the data really arrives," admits Didier Queloz.

This should not be long according to ESA, which estimates that "the first results of Cheops should reach us fairly quickly, in a few months".

© 2019 AFP