Of the six planets orbiting the star TOI-178, five are located at the resonance position of 18:9:6:4:3, about 200 light-years apart. This means that one completes 18 tracks, the other completes 9 times, and so on. However, the harmony of its orbital motion does not match the usual density that dancers usually have, which challenges the current theory of planet formation.
For the first time, an international team of astronomers observed YOU-178, Is a star about 200 light-years away in the sculptor’s constellation, and they think they have seen two planets orbiting it. However, when they investigated it more deeply, they found that it has more functions: Six exoplanets, Five of them “jump” up, and there is also a strange rhythm.
“We realize that there are many planets with very special structures”, dice Adrien LeleuScientists from the University of Geneva and the University of Berne (Switzerland) led the new research on this planetary system, which was published this week in the journal Astronomy and Astrophysics.
The authors revealed that five of the six exoplanets (except for the one closest to the star) are prisoners of rhythmic dance because they move in orbits. In other words, they are sympathetic. This means that some patterns will repeat as the planet moves, so that some patterns will line up in a straight line every few revolutions.
In order to visualize and “hear” the rhythmic movement of the planets surrounding the central star, the author expresses it through the harmony of music. Each planet has a musical note, and each planet makes a sound when it completes a full or half orbit. Planets aiming at these points will resonate.
Similar resonances were observed in the orbits of the three planets. The moons of Jupiter: Io, Europa and Ganymede. Io is the three planets closest to Jupiter in Jupiter. Io completes four orbits around Jupiter for each orbit of Ganymede, which is the slowest, while each orbit of Europa completes two. Complete track. However, the five exoplanets of the TOI-178 system follow a much more complex resonance chain, which is the longest one found in the planetary system.
When the three moons of Jupiter resonate at a speed of 4:2:1, the five outer planets of the TOI-178 system follow 18: 9: 6: 4: 3 string. This means that when the star’s second planet (the first in the resonance chain) completes 18 orbits, the third planet (the second in the resonance chain) completes 9 orbits, and so on.
In fact, initially, scientists only found five planets in the system, but according to this resonance rhythm, they calculated where they might look for another planet when there is an observation window.
The resonant planetary dance is not only the curiosity of the orbit, but also provides clues to the past of the system. “The track of the system is in order, which tells us that the system has developed in a smooth manner since its birth. “The co-author explained. Yann Alibert From the University of Bern.
If the system suffered major disturbances in the early stages of its formation, such as a huge impact, then this fragile track structure will not be spared.
The co-authors say that although the orbits are clearly arranged and organized, the density (size and mass) of the planets is “more chaotic.” Nathan Hara A researcher from the University of Geneva (Switzerland) added: “It seems that there is a planet as dense as the Earth, next to a very spongy planet with half the density of Neptune, followed by a planet with a density of Neptune. This is not what we are used to.
For example, in our solar system, the planets are perfectly arranged, the rocky planets are closer to the central star, and the fluffy, low-density gas planets are further away.
Leleu believes that “this contrast between the rhythmic harmony of orbital motion and the disordered density undoubtedly challenges our understanding of the formation and evolution of planetary systems.”
Researchers believe that this system can provide important clues about how planets (including planets in the solar system) formed and evolved.
Observation from the ground and space
In order to study the unconventional architecture of the system, the team used The CHEOPS satellite of the European Space Agency (ESA)With the instrument Strong coffee,installed at The Very Large Telescope (VLT) of the European Southern Observatory (ESO)And telescope NGTS with specification, Are located in the Paranal Observatory in Chile.
Because exoplanets are difficult to detect directly with telescopes, astronomers use other techniques.The two main methods are Image transit (Observe the light emitted by the central star. When viewed from the earth, the star will dim when the exoplanet passes over the central star) Radial velocity (Look at the star’s spectrum for signs of tiny wobbles as the exoplanet moves in its orbit).
In this case, the team used two methods to observe the system: CHEOPS, NGTS and SPECULOOS for transportation, and ESPRESSO for radial velocity.
By combining these two technologies, scientists are able to collect key information about the system and its planets. This information orbits its central star closer and faster than the Earth orbits the sun. The slowest takes about ten times the time.
The size of these six planets is about one to three times the size of the earth, and their mass is 1.5 to 30 times that of the earth. Some exoplanets are rocky but larger than Earth (nicknamed Super Earth). Others are gaseous, just like the outer planets of our solar system, but with a smaller volume (tiny tune).
Although none of the six exoplanets found are in the habitable zone of stars, the researchers, including some of them Institute of Astrophysics of the Canary Islands (IAC), Suggesting that they can find more or very close planets in the area in the future. ESO’s future very large telescope (ELT), which will begin operation this decade, may help with this task.
The Cheops space satellite and other instruments on the ground revealed unique planetary systems. / ESA / Cheops Mission Consortium / A. Leleu, etc.
A. Leleu et al., “The six planets and the Laplacian resonance chain of planets in TOI-178”. Astronomy and Astrophysics, 2021.