The inclination of the planet’s orbitHow this occurs is one of the great mysteries in planetary science. Changes in orbits due to gravitational interactions between planets are one of the most likely mechanisms, but there are still some details that are not clear.
A research team led by Yale University’s Malena Rice has discovered that extrasolar planets areTOI-2202 b“ofAs a result of measuring the inclination of the orbit, it is considerably tilted at approximately 26 degrees.We measured that. TOI-2202 b is predicted to be in a state of orbital resonance, where its orbit is difficult to change. This research result is a very important discovery because it does not agree with the hypothesis that the orbit tilts due to gravitational interaction.
[▲Figure: Conceptual diagram where the orbits of two planets are tilted with respect to the rotation axis of the star (Credit: Malena Rice)]
■There are many mysteries as to why the orbits of planets are tilted.
If we measure the inclinations of the orbits of the planets in our solar system relative to the sun’s equator, all eight planets (excluding Pluto, which was once classified as a planet) fall within 10 degrees. On the other hand, when we similarly examine the inclinations of the orbits of planetary systems other than the solar system, it is known that approximately one-third of them are extremely tilted.
At the site where a star is born, a protoplanetary disk exists around the star, and planets are born within it. The rotation of the protoplanetary disk coincides with the rotation of the central star, so the planet’s orbit should not be tilted much from the star’s equator. Therefore, it is expected that some other mechanism is at work for the creation of planetary systems with extremely tilted orbits.
The mechanisms considered to be promising are as follows. When there are multiple planets, the distances between the planets become closer during repeated revolutions, and their orbits may be disrupted by gravitational interactions. It is thought that this disturbance in the orbit causes an extremely tilted orbit.
However, it is difficult to measure the inclination of the orbits of exoplanets, and so far the orbits of only about 100 planetary systems have been determined. This small number has made it difficult to build detailed models of changes in orbits, and studies of mechanisms have not been successful.
■Discovered the extreme inclination of TOI-2202 b’s orbit!
Rice’s research team has discovered that extrasolar planetsTOI-2202 b” measured the degree of orbital inclination. TOI-2202 b revolves around the star TOI-2202, which is approximately 770 light-years away in the constellation Aquarius as seen from Earth. The research team used the Minerva Austreilis telescope at Mt Kent Observatory (Queensland, Australia) to measure the Rossiter-McLaughlin effect
in which the light from TOI-2202 changes as the planet orbits. Since the changes are small, precise observation is required, but it is possible to investigate the inclination of the orbit.
*…When observing a rotating star from a distance, one hemisphere appears to be approaching the observer and the other hemisphere appears to be moving away from the observer, so the light from the approaching hemisphere is blue-polarized due to the Doppler effect. The light from the hemisphere moving away from you is redshifted. When a planet passes in front of a star, light from either the blueshifted side or the redshifted side is blocked, causing a bias in the wavelength of the star’s light. This difference in the Doppler effect that appears in wavelength is the Rossiter-McLaughlin effect. By observing this effect, it is possible to measure how tilted the planet’s orbit is.Rice et al.The inclination of TOI-2202 b’s orbit is approximately 26 degrees (11 to 38 degrees).
Did. This is an unexpected discovery considering the planetary system of TOI-2202. In addition to TOI-2202 b, which was observed this time, there is another planet, TOI-2202 c, around TOI-2202, and each planet has an orbital resonance relationship of 2:1. It is believed that there is.Orbital resonance is caused by the mechanical stability of the gravitational interactions between planets. On the other hand, in a planetary system where orbital resonance occurs, dynamically unstable situations that drastically change the orbits occur. It is considered not to do so. In other words,TOI-2202’s planetary system has hardly changed since its birth, and the mechanism of “orbit disturbance due to gravitational interaction” proposed to explain the reason for the tilt of the orbit does not apply.
It will be. On the other hand, it is a coincidence that the planetary system of TOI-2202 appears to be in orbital resonance, and it is possible that it is not actually in such a state, so more detailed research is required.
Related article: Six planets that resonate with “HD 110067” discovered, important “fossils” in planetary science (December 10, 2023)
There are many exoplanets whose formation mechanisms are unknown, including “hot Jupiters,” which are Jupiter-like planets with orbits extremely close to their stars. The measurement of the inclination of TOI-2202 b’s orbit is the first measurement of the inclination of the orbit of a planetary system close to orbital resonance, and it can be said that research has just begun. As the inclinations of the orbits of other planetary systems are measured, clues to solving this mystery will likely increase.
Source
Written by Riri Aya
