The astronomer leading the search for a second planet Earth

A few numbers are enough to express how alone we humans seem to be in the universe. According to conservative calculations, in our galaxy alone, the Milky Way, there are 300 million planets similar to ours, on which there would be liquid water and, therefore, the possibility of life. Since 1995, Earthlings have built increasingly powerful telescopes that have allowed us to discover the overwhelming number of 5,602 exoplanets beyond our solar system. Among all of them, only a few dozen have the right size, mass and rock composition, and even fewer orbit stars like the Sun. The number of planets actually similar or identical to ours identified so far is even more disappointing: zero.

Finding a twin planet of Earth would deal a mortal blow to the narrative of many religions, including Christianity, and would show us that we are not unique or special in the cosmos. But making a discovery like this is a devilish task. In our galaxy there are about 20 billion G-type stars, like our Sun. You would have to look at them all for an entire year to detect the

orbiting

earths

; and at least another year to confirm them. In addition to this insurmountable challenge, the best current telescopes, including the brand new

James Webb

,

are at the limit of their capacity when it comes to seeing these worlds.

“If we analyze the spectacular results of the

Webb

since its launch and look at those that have come from more or less small planets with more or less tenuous signals, most of them, almost 100%, are not conclusive,” he explains by videoconference. Ignasi Ribas (Manresa, 53 years old), director of the Institute of Spatial Studies of Catalonia and researcher at the CSIC. “Researchers see signals that could be the atmosphere of a terrestrial planet or due to stellar activity, but they do not know how to distinguish them. And this is the drama,” he confesses.

Ribas is one of the most veteran exoplanet discoverers in our country, with more than 70 new worlds in his personal account. He has now just won a prestigious grant of 2.5 million euros from the European Research Council to reverse this situation and multiply by 10 the observation capacity of current telescopes.

The problem is not detection technology, which has progressively improved, but stellar activity. Stars like the Sun are changeable. They have spots that move across their entire surface. They also present faculae, or regions that are brighter than the rest of the star. This variability introduces signals that make it difficult or impossible to distinguish the light reflected by a planet from that coming directly from its star. This “noise” makes it difficult to directly observe the planet when it passes in front of its star, known as transit, as well as the study of the small oscillations produced by the gravitational influence of a planet orbiting its star, known as radial velocity. The resolution of both techniques has been stalled for around a decade, explains Ribas.

“I'm putting my little finger on the fact that we have already discovered stars that have

lands

and we are not seeing them because it is tremendously difficult to clean up all the noise in the signal,” he says. “The atmospheres of cold stars are rich in water vapor. If you see these signs, you may not know whether it is water in the planet's atmosphere or in the star itself. What we want with this project is to jump over this barrier that stellar activity imposes on us. Provide the tools to reach an instrumental precision ten times greater than the current one,” he details.

Ribas' project is called Spotless and will last five years. It consists of creating digital simulations of the most interesting stars with all their spots and faculae. The team would observe the star for a few months before, for example, the transit of a possible planet Earth occurs. “As we will have a superfine star model, we will be able to do millions of simulations and tell an artificial intelligence machine learning algorithm: here are the possibilities of variation of a star of this type and here are some observations. Tell me what part of the variations in these observations are attributable to the activity of the star and what others are the presence of a planet,” says Ribas.

The astrophysicist explains that his team has been doing this work for around a decade in a more or less organized way. The new funding will make it possible to hire eight researchers who will join the four who were already involved in this project and to be able to carry it out in a more systematic way. The first step will be to validate a new star model using the Sun as a reference. Afterwards, other models of nearby solar stars will be built. “At first we will stretch the gum a little with planets a little larger or smaller than the Earth in stars that may also be approximately like the Sun, but in the end we will be able to search for worlds very similar or identical to ours,” explains Ribas.

The project will focus on data collected by the Espresso instrument on the Very Large Telescope in Chile, which searches for planets using radial velocity, and infrared light data from the

James Webb

. In 2026, the European Space Agency will launch the

Plato

telescope into space

, specially designed to search for terrestrial planets in hundreds of stars like the Sun, which will add a new data bank to apply the new models.

Ribas believes that the first “exo-Earths” will almost certainly be discovered within about five years. But the danger of staying just at the gates of the greatest discovery imaginable will still be there. “If we are lucky enough that the new planet is in a tremendous star quite close to our planet, it will be easy to use the

James Webb

to characterize its atmosphere and look for water vapor, but if it is a weaker and more distant star, we may not have sufficient resolution.”

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