An international team of astronomers has announced the discovery of an unusual exoplanet, designated TOI-6894b. It is capable of challenging modern theories of planet formation.
Gas giant near a tiny star
The discovery was made during an analysis of data collected by the TESS telescope. It detected periodic decreases in the brightness of the red dwarf TOI-689. It is a small, cold star with a mass of only 20% that of the Sun. Every 3.4 days, its brightness decreases by as much as 17%.
During subsequent observations carried out using ESO’s Very Large Telescope, it was confirmed that the changes in brightness of the red dwarf were caused by transits of an exoplanet orbiting it. Its characteristics surprised scientists. It turned out to be a bloated gas giant: an exoplanet that is slightly larger than Saturn in size, but whose mass is about half that of Saturn.
The discovery is important because TOI-6894 is currently the smallest star known to host such a large exoplanet. For comparison, the previous record holder was one and a half times larger.
Challenging the theory
According to the researchers, they do not fully understand how a star with such a low mass could form such a massive planet. The most widely accepted theory of exoplanet formation is called the core accretion theory. According to this theory, a planetary core is formed first, which then attracts the gases that form the atmosphere. When it becomes massive enough, the process of uncontrolled gas accretion begins. As a result, a gas giant is formed.
At the same time, according to modern ideas, protoplanetary disks around low-mass stars do not contain enough material to form a sufficiently massive core to initiate the accretion process.
However, the existence of TOI-6894b suggests that this model cannot be entirely accurate and that alternative explanations are needed. One of them is the model of a gravitationally unstable disk. According to it, in some cases, the protoplanetary disk becomes unstable due to the gravitational force it exerts on itself. It can then fragment, and the gas and dust collapse to form a planet.
However, in the case of TOI-6894b, none of the theories can yet fully explain the formation of the exoplanet based on the available data. Scientists hope to find some clues by analyzing its atmosphere. By measuring the distribution of matter inside the planet, they will be able to determine the size and structure of the planet’s core, which will help determine whether TOI-6894b formed through accretion or through instability in the disk.
The James Webb Telescope can help solve this problem. Given the depth of the transits, TOI-6894b is an ideal candidate for its observations. What makes it even more interesting is that the temperature of the exoplanet’s atmosphere is only 150 °C, which is much lower than that of most other gas giants known to us. All this makes TOI-6894b one of the most promising targets for future study.
Earlier, we discussed whether life could exist in red dwarf systems.According to Phys.org
