Astronomers discover a system of 6 planets with a near perfect orbit

Astronomers have come up with a particularly special find: a system featuring the star HD 158259 and six planets that maintain an almost perfect orbit around it.

The team has presented the results of seven years of close observation in an article in the journal Astronomy & Astrophysics. On this occasion, they highlight the importance of the finding beyond the broad scope of current technology; and it is that this, in particular, could help us to better understand how planetary systems are formed and the processes they go through until they reach their configurations.

Orbital resonance

As many know, our solar system is not the only one in the universe. Astronomers have discovered hundreds of stars similar to our sun in our galaxy, around which multiple planets as diverse as those closest to our own orbit.

But a special case has dazzled the astronomers who studied it: a planetary system located 88 light-years away, whose star is practically the same as ours. HD 158259 has almost the same mass as the Sun, only slightly exceeding it in size, and has six planets orbiting, including one similar to Earth but slightly larger, and five more similar to a small Neptune.

Before continuing, it is convenient to talk about orbital resonance. It is a type of coordination that occurs when the orbits of two bodies around their central body are closely related so that the two bodies exert a gravitational influence on each other.

In our Solar System, this coordination is not very common to say, although we can cite as an example Pluto and Neptune, which seem to be synchronized. Neptune circles the Sun three times for every two times that of Pluto.

The orbit of one of the planets of the system resonates almost perfectly

While studying the new system, astronomers set out to accurately calculate the orbits of each planet. To do this, they used measurements made with the SOPHIE spectrograph and the TESS exoplanet-hunting space telescope.

In the planetary system described in the new paper, the orbit of each planet appears to be coordinated with that of the others in an almost perfect relationship. The researchers write that the orbital resonance is also nearly 3: 2 between planets, or a period of 1.5, so that for every three orbits each makes, another makes two.

The researchers explain that the planets in the system are tightly packed despite the near-perfect resonance of each other's orbit. The closest planet to HD 158259, a larger version of our planet, is about twice the mass of Earth. Starting from it, the orbits are 2.17, 3.4, 5.2, 7.9, 12, and 17.4 days, producing period ratios of 1.57, 1.51, 1.53, 1.51, and 1.44 between each pair of planets.

For the team, this is not a perfect resonance, but what really is from our perspective of the universe? Although it is not, it is close to being it, which has deserved to classify the HD 158259 system as extraordinary.

What orbital resonance reveals about planetary systems

Now, the finding leaves us a message between the lines. The researchers believe that this peculiar orbital configuration is a sign that the planets orbiting the star have not always been like this.

"Several compact systems with several planets at or near resonances are known, such as TRAPPIST-1 or Kepler-80," explained astronomer Stephane Udry of the University of Geneva. “Such systems are believed to form far from the star before migrating towards it. In this scenario, resonances play a crucial role ”.

One hypothesis suggests that when planets are born, they do so within protoplanetary disks. As they grow, they migrate inward away from the outer edge of the disk.

Under this dynamic, an orbital resonance chain would occur throughout the planetary system. However, the final dissipation of the gas from the disk produces a stimulus that destabilizes the orbital resonances established initially. That is why scientists believe that studying this aspect can reveal a lot about the beginnings of a particular system.

Reference: The SOPHIE search for northern extrasolar planets