The signal was observed by the European LOFAR radio telescope, a network of 50,000 antennas spread across Europe and operating at very low frequencies, a field of energy still little exploited. The show comes from an already known system, Tau Bootis, located 50 light years away, the “immediate suburb” of our solar system. It contains a double star and a gas giant exoplanet orbiting nearby: a “hot Jupiter”, called Tau Bootis-b.
The mass and orbit of many exoplanets is already known, but until now there was no way to know whether or not they have a magnetic field. We find this shield, protecting from the radiation of stellar winds, around the Earth and “our” Jupiter. However, the radio program captured by LOFAR “is a very precise signature of the magnetic field”, explains to AFP Philippe Zarka, of the Paris Observatory – PSL, one of the main authors of the study published this week in Astronomy & Astrophysics . These waves are very difficult to detect, planetary magnetic fields are generally weak and their source of emission distant.
The international team that carried out the research therefore observed three extrasolar systems (Tau Bootis, 55 Cancri and Ups) containing gas giants which, because they are close to their star, are probably powerful emitters. Taking as a model the radio signal from our Jupiter, attenuated to the maximum, the analysis of a hundred hours of observation pleaded in favor of the expected signature of Tau Bootis.
“There is a 98% chance that the signal will be reliable,” comments Philippe Zarka, adding that there is a slight doubt that the signal emanates not from the planet, but from its star. “To be really sure, it would take a 99.9% chance. We will have to continue the observations, which is within our reach, ”adds the astrophysicist.
If the emission is true, “it would be a first which will validate the radio detection technique, and therefore a step towards the characterization of exoplanets”, underlines the researcher.
Almost 4,000 exoplanets have been detected since the discovery of the first, 51 Pegasi b, 25 years ago.
The existence of a magnetic “bubble” around them is an ingredient favorable to “habitability”, that is to say conducive to the development of a form of life, adds Philippe Zarka. But there are other criteria, such as temperature, and in this case Tau Bootis b. would be too hot to harbor life.