YZ Ceti b may be the first planet beyond the solar system with a magnetic field detected through radio waves. It is the innermost of three Earth-mass planets around YZ Ceti, a small red dwarf about 12 light-years away, and orbits the star in about two days.
It was found together with its siblings YZ Ceti c and d in 2017 by a team led by N. Astudillo-Defru using the HARPS spectrograph in Chile. They used the radial velocity method, which detects the slight back-and-forth motion a planet's gravity gives its star. The planets' minimum masses were then among the lowest ever measured that way. Pinning down the orbits was hard, because the timing of the observations allowed more than one period to fit the data, a problem called aliasing. In 2020 a CARMENES team led by S. Stock added 229 new measurements and settled the question: YZ Ceti b orbits every 2.02 days, and its minimum mass is about 0.7 Earth masses.
Its radio story began in 2023. A team led by J. Sebastian Pineda detected bursts of radio waves from the star, two of them at similar points in YZ Ceti b's orbit. A separate team led by Corrado Trigilio, observing at lower frequencies with the Giant Metrewave Radio Telescope, also linked radio bursts to the planet's orbit. The idea is that the planet, orbiting inside the star's magnetic field, disturbs it and triggers the radio emission. Trigilio's team concluded the interaction is confirmed and that the planet must have its own magnetic field, which can help shield an atmosphere. Pineda's team was more cautious: they could not rule out ordinary activity on the star and called it a candidate. A 2025 study mapping the star's magnetic field found that it changes over just a few rotations, which matters for interpreting the signal. At two days from its star, YZ Ceti b is far too hot for liquid water.