• The European Space Agency is working on a new mission that will leave in 2026 in search of "a second Earth in the Universe".
  • The Plato telescope will look at the stars hoping to observe the "transits" of habitable exoplanets, that is to say the light variations that occur when an object crosses a field of view "as during an eclipse".
  • "It is thought that there is, on average, one planet per star. And it is estimated that there are at least 100 billion stars per galaxy and perhaps 2,000 billion galaxies. It really leaves a lot of possibilities," says Jean-Luc Petit, former head of the Plato program at Thales Alenia Space, the satellite's manufacturer.

Is there, in the vastness of the cosmos, a twin of the Earth? Another place where life could have developed, in one form or another. For more than thirty years, observations of exoplanets (5,346 recorded to date) and promises to discover an almost incalculable number of them have led scientists to imagine that no, we would not be alone in the Universe.



In Cannes, at satellite manufacturer Thales Alenia Space (TAS), the European Space Agency (ESA) is working on a new mission that will go in search of "a second Earth in the Universe". Or at least other "habitable" environments outside our solar system. 20 Minutes was able to go to the clean rooms where the Plato telescope and its 26 eyes ready to scan the far reaches of our galaxy are being prepared.

What is a "habitable" planet?

As of March 31, 5,346 exoplanets had already been observed and recorded. A drop in the ocean. "It is thought that there is, on average, one planet per star. And it is estimated that there are at least 100 billion stars per galaxy and perhaps 2,000 billion galaxies. It really leaves a lot of possibilities," says Jean-Luc Petit, former head of the Plato program at Thales Alenia Space, where vibration tests of the satellite's solar generators have just been organized.


The @esa #Plato telescope will leave in 2026 in search of new #exoplanetes. It will be assembled in the @Thales_Alenia_S clean room in @villecannes, where initial vibration resistance tests have already been carried out #verslinfinietaudela pic.twitter.com/L0TnymPC4g

— Fabien Binacchi (@fabienbinacchi) April 3, 2023

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And among this figure of 23 zeros of potential candidates, "it is estimated that one in five is in a habitable zone," says the specialist. With Plato, ESA will target the regions surrounding the stars known as "goldilocks". Not too close, not too close, but where "the temperature is ideal for liquid water to exist on the surface of a planet". Which will obviously have to be telluric, that is to say made of rock.

How will the Plato telescope work?

To raise the exoplanet counter, Plato will look at the stars hoping to observe their "transits", when the planet orbits them. The telescope and its 26 cameras, which will make it possible to create mosaics of images of nearly 2 billion pixels, will focus on photometry, that is to say the luminous variations of the celestial bodies observed. With a simple rule: if their brightness decreases at regular intervals, it is because something comes to block the view. "Like during an eclipse," says Jean-Luc Petit. And the magnitude of this decrease will make it possible to specify the size of the object in question. »

The first two missions launched to discover exoplanets, CoRot between 2006 and 2014, and Kepler from 2009 to 2018, used the same process. But Plato will offer unparalleled accuracy with a "unique ability to be able to make stable and very long-lasting observations," boasts Thales Alenia Space. "The accuracy of the scoring will be extremely high," says Catherine Vogel, the new head of the Plato program at TAS. A sine qua non condition for obtaining reliable data, which the satellite will support thanks to asteroseismology. This "study of the sound waves that pass through stars and make them vibrate" makes it possible to determine their mass, age and radius. Essential information to characterize the planets that revolve around them.


The same areas scrutinized for more than two years

The mission is expected to take off aboard Ariane 62 from Kourou, French Guiana, at the end of 2026. Placed in a heliocentric orbit, that is to say around the sun, at the L2 Lagrangian point, 1.5 million kilometers from Earth, the telescope will focus on a field of space (much wider than in previous missions) for two and a half years, before changing. "If we want to find planets with characteristics close to those of the Earth, we must count on orbits of the same duration. It therefore takes at least two years, and the observation of two transits, to confirm their presence around the stars that the satellite will look at, "says Jean-Luc Petit.

As the mission is planned for at least six years, ESA hopes to be able to analyse at least two different areas. "We will target areas in which stars have similarities with the sun, to give ourselves the maximum chance of finding habitable planets. But all this is not yet fixed, adds Catherine Vogel. Specialists are still thinking about the best places to explore. We are a bit like in the time of Christophe Collomb. We're really into exploration."

  • Sciences
  • Nice
  • Alpes-Maritimes
  • PACA
  • Cannes
  • Space
  • Exoplanete
  • Space conquest