Monday , March 8 2021

The mysterious hexagonal system has confused astronomers

Using data from the very large binoculars of the European Southern Observatory (ESO VLT), astronomers have discovered a planetary system orbiting about five of its six planets in a sparse, coordinated rhythm. Researchers believe the system could provide important information about the origin and evolution of planets, including the celestial bodies of the solar system.

When the research team first observed it in the constellation Sculptor, an eye was spotted. It was thought to have been captured 200 light-years from the catalog star TOI-178 by two planets orbiting the same orbit. However, a closer examination revealed a completely different situation. “Based on further observations, we realized that they are not two planets orbiting at almost the same distance from the star, but several planets in a very special configuration,” says Adrien Leleu (University of Geneva, University of Bern, Switzerland), published today in Astronomy & Astrophysics. , the lead author of a study representing the system.

Planets in resonance

New research has found that the system has six planets orbiting in a tightly connected rhythm, other than the one closest to the star. In a technical sense, they resonate. This means that during the orbit around the star, certain configurations are regularly repeated, with some planets reappearing in the same direction after several orbits seen from the star. A similar resonance can be observed in the three months of Jupiter, Io, Europe, and Ganymede. Of the three, Io closest to Jupiter makes four and two full orbits, respectively, while the most distant Ganymede and Europa make up one.

The artistic idea of ​​the TOI-178 systemSource: ESO / L. Calçada /

The five outer planets of the TOI-178 system are much more complex, characterized by one of the longest resonant chains observed to date for exoplanet systems. While Jupiter’s three moons resonate with each other in a 4: 2: 1 ratio, the five outer planets TOI-178 can be described by a chain 18: 9: 6: 4: 3: while the second planet from the star (first in the resonant chain) 18 orbits, the third planet (second in resonant chain) 9 orbits and so on. At first, the researchers actually identified only five planets in the system, but following a resonant rhythm, they calculated where another planet would be in its orbit when they had a chance to observe the system again.

The resonant dance of the planets is more than celestial mechanical curiosity, as it also brings information about the system’s past. “The trajectories in the system are very nicely arranged, suggesting that it has evolved without major shocks since its birth,” explains Yann Alibert (University of Bern), one of the co-authors of the article. If the system had previously been more disrupted, like a massive impact shape, the fragile track configuration would not have survived it.

Clutter okay

Although the orbits follow each other in good order, the same can no longer be said for the density of the planets, they are “much more messy,” says Nathan Hara (University of Geneva, Switzerland), who is also included in the study as on Earth, but one that the immediately following is only half the density of Neptune, while the one that follows is equal to Neptune’s. “For example, in the solar system, the arrangement of the planets is much nicer, the denser rock planets are closer to the central star, and the low-density gas giants orbit from it.

“The contrast between the rhythmic harmony of circulation and the confusion of density poses a serious challenge to our theories that explain the origin and evolution of planetary systems,” Leleu adds.

A combination of methods

In addition to the European Space Agency’s (ESA) CHEOPS spacecraft, the research team used ESPRESSO, which operates on ESO’s VLT telescope complex, and NGTS (Next Generation Transit Exploration) and SPECULOOS (Search for Habitable ULtra-cOOl Stars). Because exoplanets are extremely difficult to observe directly, astronomers must use other techniques to detect them. The two most important procedures are the so-called transit observation and the measurement of radial velocities. The first reveals a decrease in the brightness of the central star as its planet passes in front of the Earth, while the second measures a periodic shift in the spectral lines of the star as the planet “pulls” the central celestial body as it orbits. NGTS and SPECULOOS measured transits, ESPRESSO measured radial velocity changes.

The figure shows the position of the planetary system TOI-178 in the constellation Sculptor. The map shows most of the stars visible to the naked eye in good conditions, the celestial position of the planetary system is marked with a red circleForrás: ESO, IAU and Sky & Telescope

By combining the two methods, astronomers have been able to gather the most important information about the system and its planets, each of which orbits much closer to its star than the distance of the Sun and Earth and orbits much faster than our planet does. The fastest (innermost) planet makes a circle in just a few days, while the slowest takes approximately. you need ten times as much time. The size of the six planets is approximately between Earth and three times larger than them, while their masses are between 1.5 and 30 Earth masses. Some of the rock planets larger than Earth, these are the so-called super-land, and other gas planets are similar to the outer planets of the solar system, but smaller than them, these are the so-called. minineptunes.

Although none of the six planets orbit the star’s habitable zone, the researchers say that by continuing the resonance chain, they may still find additional planets in the system located in or near the zone. ESO’s Extremely Large Binoculars (ELT), which will be operational this decade, will be able to directly photograph rock planets orbiting residential neighborhoods and even determine the characteristics of their atmosphere, allowing for even more detailed testing of systems like the TOI-178.

Source: ESO

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