The Kepler-11 system, as imagined from above, is a “peas-in-a-pod” planetary system. Credit: NASA
Astronomes have discovered more than 300 exoplanetary systems that have three or more well -known planets. Most of these planets have about the same dimensions and distantly distanced, gaining the moniker “Peas in a pod”. They also orbit near their stars, in many cases closer than Mercury in the sun.
Our solar system, on the contrary, seems to be different.
“[Planetary scientists] I thought that our sun system is not standard in its distances, “says astronomer Juliette Becker of the University of Wisconsin-Madison. In particular, the rocky planets are not as close as in other systems, there is a large gap (the main belt) between Mars and Jupiter, and giant planets are not also very close close.
But a new study by Becker and a team of researchers suggests that our sun system is not as unusual as it was previously thought. The study, published in The astronomical diaryIt is the first to use the entire catalog of Esoplaneti to examine the architecture of planetary systems.
Like peas in a pod
To order the planetary systems in groups, the team examined both the size of the exoplanets and their vintage relationships-the number of days in which a certain planet takes for orbit its star divided by the number of days in which the planet closest to the star in orbit-like brings how the measures approach the worlds.
In total, about 80 percent of systems with three or more planets adapt to the Peas-in-a-Pod category.
“There is no rigorous criterion for [whether] Something is or is not peas in a pod, “says Becker.
The team considered pea systems in a pod even if their planets are not perfectly distanced. For example, Kepler-11 has six known planets that complete an orbit around their star in about 10, 13, 23, 32, 47 and 118 days (periodic ratios of 1.3, 1.7, 1.4, 1.5 and 2.5, respectively). In our Solar System, Mercury, Venus, Earth and Mars have periods of approximately 2.6, 1.6 and 1.9 respectively.
Overall, the study has shown that our solar system is reasonably well suited to the Team’s Peas-in-A-Pod category.
Division line
Some pea systems in a pod also have external planets such as our sun system. Deciding on a rule to designate the internal and external regions was not easy, but the team ranked the external planets such as those that take more than 130 days to orbit the stars and are separated from periodic ratios exceeding 5.
These double conditions have solved some planets in internal regions, despite being separated by large gaps. The researchers called these systems that thrown the peas in a pod. Kepler-62 is an example, with five planets taking about 6, 12, 18, 122 and 267 days to orbit their star (reports of a period of 2.2, 1.5, 6.7 and 2.2, respectively).
“It is possible that some of those gaps are planets that we have not yet detected,” says the planetary scientist André Izidoro of Rice University, who was not involved in the study.
Some of the single systems and two planets that the team has classified could also have more planets smaller than Jupiter, and therefore in the end being reassigned in the Peas-in-a-Pod category.
The team also created a separate category called “Warm Jupiter” systems for those who have larger planets than Jupiter in the internal regions with smaller planets. The further distinction was to take into account the greater variability of the masses and the relationships of the period of these planets.
Overall, the team was able to classify about 97 percent of planetary systems with three or more planets. The classification scheme is also large enough to include smaller planets that could be discovered with more powerful telescopes in the future.
Architecture of the formation of planets
The new classification scheme is also useful for understanding how planetary systems evolve. For example, the team was able to distinguish the pea-in-a-pod systems from the hot systems of Jupiter.
“This is an important step in an attempt to understand how these planetary systems come to these [peas in a pod] Favorite architectures, “says the planetary scientist Darryl Seligman of Michigan State University, who was not involved in the study.” Perhaps the hot jupuries prevent him “.
Peas in a pod, with their planets of similar size, could also imply a common physical process on how their planets grew by the grains of dust. In the process, these systems may have undergone collisions and further growth.
“What surprises these systems is that even if they experience instability, they can still preserve their peas agreements in a pod as we have seen in the simulations,” says Izidoro.
Divides the systems in groups also has the advantage of identifying the anomalous values, which can invoke researchers to think of the single process through which the planets form and evolve.
For example, Trappist-1 and Kepler-42 are miniature peas systems, the latter with planets completing an orbit in less than two days.
“The breakdown of a classification scheme is sometimes what pushes science forward,” says Seligman.
Many efforts have been made to classify the almost 6,000 exoplanets discovered to date in size and orbital period. But examine their systems as objects has been limited.
“In reality it is really difficult to get enough planets to start building categories and trying to understand what are the groups of existing planets,” says Becker. “We are really in an exciting moment.”
