An impossible planet – Meson Stars

Based on current scientific knowledge of planet formation, TOI-5205b should not exist. Yet there it is. A team of astronomers, led by Shubham Kanodia of the Carnegie Institution of Science in the United States, has discovered an unusual planetary system in which a large gas giant planet (TOI-5205b) orbits a small red dwarf named TOI-5205. The finding challenges long-held ideas about planet formation. Smaller and cooler than our Sun, M dwarfs are the most common stars in our Milky Way galaxy. Due to their small size, these stars tend to be about half as hot as the Sun and much redder. They have very low luminosities, but extremely long lives. Although red dwarf stars host more planets, on average, than other types of more massive stars, their formation histories make them unlikely candidates for surrounding gas giant planets.

NASA’s Transiting Exoplanet Survey Satellite (TESS) identified TOI-5205b as a possible planet for the first time. The Kanodia team, which includes Anjali Piette, Alan Boss, Johanna Teske and John Chambers of the Carnegie Institution of Science, later confirmed its planetary nature and observed it in more detail, using various ground-based instruments and facilities. TOI-5205, the star around which the planet orbits, is barely four times the diameter of Jupiter, yet a Jupiter-sized planet formed around it. This is surprising because it was believed that planets with such a mass could not form around low-mass stars.

A few gas giant planets are known to orbit M dwarf stars. But until now no gas giant planets have been found around an M dwarf as low in mass as TOI-5205.

This smaller than normal mass difference is also reflected in the sizes. When the Jupiter-mass TOI-5205b crosses in front of its star (from Earth’s visual perspective) it blocks about seven percent of its light. It is one of the largest blocked star portions of all cases of planets passing in front of their star. Planets are forged in the spinning disk of gas and dust that surrounds young stars. According to the most accepted theory on the formation of gaseous planets, a mass of this material, about 10 times greater than the mass of the Earth, is required to accumulate and form a massive rocky core, after which the protoplanet quickly sucks up large amounts of gas from neighboring regions of the disk to form a gas giant planet like the ones we see today.

The time frame in which this occurs is crucial. “The existence of TOI-5205b changes what we know about the disks in which these planets are born,” explains Kanodia. “In the beginning, if there isn’t enough rocky material in the disk to form the initial core, then a gas giant planet can’t form. And in the end, if the disk dissipates before the massive core forms, neither can it.” already form a gas giant planet. However, TOI-5205b formed despite these limitations. Based on current knowledge of planet formation, TOI-5205b should not exist; it is a ‘forbidden’ planet.” Either something extraordinary happened in the TOI-5205 system that allowed these restrictions to be overcome, or current scientific knowledge about planet formation will have to be revised.

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