The largest and most sensitive radio telescope ever built will hunt for signals from alien life and search for extrasolar planets - or exoplanets, which have magnetic fields like our planet - within 100 light-years of Earth.

Astronomers from countries including China and France recently published their ambitious observation plan using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) in the academic journal Research in Astronomy and Astrophysics.

Li Di, a researcher at the National Astronomical Observatories of the Chinese Academy of Sciences and chief scientist of FAST, said scientists are more concerned about habitable planets, which should have not only water, a suitable temperature and atmosphere, but also a magnetic field.

"The earth's magnetic field protects life from cosmic rays. There is a scientific occurrence in the sci-fi blockbuster The Wandering Earth, in which the earth stops rotating. If that happens, the magnetic field would disappear. Without the protection of the magnetic field, the earth's atmosphere would be blown off by the solar wind. As a result, humans and most living things would be exposed to the harsh cosmic environment and would be unable to survive," Li said.

There are six planets in our solar system with a planetary-scale magnetic field: Mercury, Earth, Jupiter, Saturn, Uranus and Neptune.

"In our solar system, magnetized planets are strong radio sources," said Philippe Zarka, an astronomer from the Paris Observatory. "Radio detection of exoplanets is aimed at the physical characterization of exoplanets and comparative studies with solar system planets."

The first exoplanet was discovered near a pulsar by means of radio astronomy, but that was a very special case. All the other exoplanets found so far were discovered through optical astronomy or infrared imaging, according to Li.

Those discoveries have led scientists to believe that nearly all the stars in the Milky Way have planets revolving around them, and that there must be plenty of habitable planets.

"In our solar system, the high-energy charged particles in the solar wind and the electrons from some planets' moons would have interaction with the magnetosphere of planets, generating radio radiation," Li said. "All the planets with magnetic fields in our solar system can be found generating such radiation, which can be measured and studied by radio telescopes. But research on the planets' magnetic fields cannot be realized through optical and infrared astronomical observation.

"Do the exoplanets have magnetic fields? If so, they should also generate radio radiation under the influence of the wind of their parent stars," Li added.

Astronomers have been looking for radio signals from exoplanets but haven't discovered any yet.

"We want to try with FAST, which is the world's most sensitive radio telescope. If we can detect the radio radiation of an exoplanet for the first time and confirm its magnetic field, it would be a very important discovery," Li said. "If this observation window is opened, we would be able to study the laws of the magnetic fields of exoplanets and whether they are habitable in another aspect."

Most exoplanets have been discovered by the US Kepler space telescope. Those exoplanets are located more than 500 light-years from Earth.

In 2018, NASA launched a new planet-hunting satellite, the Transiting Exoplanet Survey Satellite (TESS), to target exoplanets closer to Earth.

"If TESS could find a large number of exoplanets, and we also track them, the possibility of discovering exoplanets with magnetic fields will increase," Li said. "We are looking for exoplanets within 100 lightyears from Earth. Once such planets are found, it would be favorable for scientists to conduct a thorough study of them, and there is even a possibility for interstellar migration." (China Daily Global)