In the email you sent us, you will also ask us if the list contains planets discovered by scientists in China. The answer to both of your questions is yes. The only condition for the candidates to be on this list, or lists, because there are several, is that they are confirmed, that is, that an article has been published proving that they are indeed exoplanets. And I mean scientific publications, that is, peer-reviewed articles.
Two lists exoplanets most consulted are this from NASA and which also contains statistics on planets discovered by US Space Agency missions and this European register, generated and maintained mainly by the French scientific community.
We’re calling exoplanets to planets orbiting stars that are not our sun. The first to be discovered around a star like the Sun was in 1995, but it is true that a few years earlier, in 1992, a planet orbiting a pulsar, a highly evolved star, was discovered. Since then, more than four thousand exoplanets have been discovered and confirmed, which are on the lists I talked about at the beginning.
All the planets we found outside our solar system are in our galaxy
It is important to realize that all the planets we have found outside our solar system are in our galaxy, because the technology we have now does not allow us to search for planets in other galaxies. Although they certainly exist, because if they exist in ours, there is nothing to make us think they are not in others.
We use several methods to search for exoplanets, but so far the most effective are transits, which is the one that allowed us to discover more planets. We also call it the eclipse method. It consists in detecting a decrease in the brightness of a star as a planet orbiting it passes in front of it.
From 2009 to 2013, the space telescope was in operation Kepler NASA is observing the same area of the sky. And over the four years, this has made it possible not only to record eclipses produced by exoplanets that have a short orbital period of several days, but also others that have longer, even months. This created a boom thousands were discovered during the discovery of exoplanets. This method of transit allows you to know the radius of the planet and the inclination of the orbit, but does not allow you to know the mass.
Since 2018, a new NASA mission has arrived, TESSwhich, like Kepler, uses the transit method to observe stars near us, that is, they are very clear. This will later allow us to study the atmosphere of the planets orbiting them with other instruments. With the transit method, about 75% of the exoplanets we know have been discovered, another 20% with the radial velocity method, which measures the fluctuations that a star orbits a planet and allows us to know the minimum mass of the planets orbiting it. There are also several methods, such as gravitational microlenses or direct imaging.
Cristina Rodriguez Lopez is a researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC)
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Coordination and writing: Victoria Toro
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