Ignasi Ribas: the astronomer leading the search for a second planet Earth | The science

A few numbers are enough to express how alone we humans seem in the Universe. According to conservative estimates, in our Milky Way galaxy alone there are 300 million planets similar to ours, which would have liquid water, and therefore the possibility of life. Since 1995, we earthlings have been building telescopes…

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

Finding Earth’s twin planet would be a death blow to the narratives of many religions, including Christianity, and would show us that we are not unique or special in the cosmos. But making such a discovery is a fiendish task. There are about 20 billion G-type stars in our galaxy, similar to our Sun. To discover them, you would have to look at them for a whole year. Earth orbital; and at least another year to confirm them. In addition to this insurmountable task, the best modern telescopes, including brand new ones, James Webb, When it comes to viewing these worlds, they are at their limits.

“If we analyze the impressive results Webb since its launch and we look at those that came from more or less small planets with more or less weak signals, most of them, almost 100%, do not give definitive results,” explains Ignasi Ribas (Manresa, 53 years old) via video conference. from the Institute of Spatial Studies of Catalonia and researcher at CSIC. “Researchers see signals that could be the atmosphere of a terrestrial planet or stellar activity, but don’t know how to distinguish them. And that’s the whole drama,” he admits.

Ribas is one of the most experienced exoplanet discoverers in our country, with more than 70 new worlds to his personal account. Now he has just received a prestigious €2.5 million grant from the European Research Council to change this situation and multiply the observing power of existing telescopes by 10 times.

The problem is not the detection technology, which is gradually improving, but the stellar activity. Stars like the Sun are changeable. They have spots that move all over their surface. They also appear as faculae, or areas that are brighter than the rest of the star. This variability creates signals that make it difficult or impossible to distinguish light reflected by a planet from light coming directly from its star. This “noise” makes it difficult to directly observe a planet as it passes in front of its star (called a transit), as well as to study the small fluctuations produced by the gravitational pull of a planet orbiting its star, known as radial velocity. . The resolution of both methods has stalled for about a decade, Ribas explains.

“I emphasize the fact that we have already discovered stars that Earth and we don’t see them because it’s extremely difficult to remove all the noise from the signal,” he says. “The atmospheres of cool 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. With this project we want to jump over the barrier that stellar activity imposes on us. To provide tools that allow us to achieve instrumental precision ten times higher than today,” he elaborates.

Ribas’ project is called Spotless and will last five years. It consists of creating digital models of the most interesting stars with all their spots and faculae. The team will observe the star for several months before, for example, a possible planet Earth transits. “Because we will have an ultra-fine model of the star, we will be able to run millions of simulations and tell the artificial intelligence machine learning algorithm: here are the possibilities of changing this type of star and some observations. Tell me how much of the variation in these observations is due to the activity of the star and how much is due to the presence of the planet,” says Ribas.

The astrophysicist explains that his team has been doing this work in a more or less organized manner for about ten years. The new funding will allow the recruitment of eight researchers, who will join the four already involved in the project and will be able to carry it out more systematically. The first step will be to test the new star model using the Sun as a reference. After this, other models of nearby solar stars will be built. “We’ll initially stretch the rubber band a bit with planets slightly larger or smaller than Earth in stars that could also be roughly similar to the Sun, but eventually we’ll be able to look for worlds very similar or identical to ours,” Ribas explains.

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 James Webb. The European Space Agency will launch the telescope into space in 2026. Dishspecifically designed to search for terrestrial planets among hundreds of stars such as the Sun, which will add a new data bank for the application of new models.

Ribas believes the first “exo-Earths” will almost certainly be discovered in about five years. But the danger of being left at the gates of the greatest discovery imaginable will still exist. “If we are lucky and the new planet ends up in a huge star quite close to our planet, it will be easy to use James Webb to characterize its atmosphere and look for water vapor, but if it’s a fainter, more distant star, we may not have enough resolution.”

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