Young, Close-in Planets Live Dangerously

First discovery of a planet orbiting its host star so closely that the planet’s magnetic field triggers radiation bursts from the star

To the point

• Close-in planets: Unlike Earth, many exoplanets orbit their star at very close distances. Little is known about their adolescence.
• Dangerous outbursts: The young planets can provoke violent flares from their star, which then backfire on the planets.
• New phenomenon: Ekaterina Ilin, a research group leader at the Max Planck Institute for Solar System Research, discovered the first planet to trigger such outbursts.

At the tender age of 10 to 150 million years, young planets go through a critical phase of development. During this time, their equally young host stars are particularly active, ejecting particles and radiation into space in extremely violent outbursts. This stellar bombardment can gradually erode the young planets’ atmospheres, destroying an important prerequisite for the emergence of life in the process. This rebellious phase of young stars poses a particular danger to planets that orbit very close to their star.

Close-in planets, with orbital periods of less than 10 days, do not exist in our own Solar System, but they account for about half of all exoplanets discovered to date. Very little is known about their early evolution because the barrage of particles and radiation from their star complicates precise observations.

Researcher Ekaterina Ilin of the Max Planck Institute for Solar System Research takes advantage of the planets’ proximity in her work. She is leading the new research group MICS (Magnetic Interactions in Systems with (Sub-)Stellar Companions). The massive eruptions themselves can easily be detected in data from space telescopes. By analysing their temporal distribution, she identified HIP 67522 b as a bizarre representative of young, close-in planets – and discovered a completely new phenomenon: Due to the close proximity, the planetary magnetic field couples into that of the star, thereby triggering the dangerous flares on the planet-facing side. Over millions of years, this effect could greatly accelerate the loss of a planet’s atmosphere.

Solar storms occur repeatedly in our solar system as well. However, since the planets of the solar system orbit at a relatively great distance from the Sun, they are not the cause of these storms; rather, the cause lies in processes occurring within the Sun itself.

Understanding Interactions, Finding Planets

The goal of further research is to understand how the interaction between a planet and a star occurs and how it affects the planet’s subsequent evolution. To uncover the underlying physical processes, the researcher will examine the magnetic interactions of a wide variety of cosmic pairs: ranging from binary stars with equal masses to star-planet pairs. The research group led by Ekaterina Ilin is also constantly improving the methods used to discover these systems. They are systematically searching for such interacting planets in data from current and future space telescopes such as Kepler, TESS, and PLATO.