According to the researchers, in the vast space of our Galaxy, it is possible to easily identify the terrestrial planets.
Is there a second Earth in the universe? Our knowledge of planetary systems is constantly growing as new technologies improve observational capabilities. To date, about four thousand planets have already been discovered outside the solar system. Their masses and radii can be used to determine the average density, but not the exact chemical composition and structure. Thus, the intriguing question of what exoplanets look like remains open.
“In theory, we can assume different compositions, such as a world made of only water, or completely rocky exoplanets, for example, with an atmosphere of hydrogen and helium, and calculate what radii such planets might have,” explains Michael Lozovsky, Ph. D. from the group of Professor Ravit Helling at the Institute of Computational Science at the University of Zurich (Switzerland).
Limiting the composition of the planets
Scientists have used databases and statistical tools to characterize exoplanets and their atmospheres. Planetary systems are quite common, however, directly measured data previously did not allow researchers to determine their exact structure, since different compositions can lead to the same mass and radius. To improve the accuracy of the data, the research team also examined the putative internal structure, temperature, and reflectivity of 83 of the known planets for which masses and radii are well defined.
Exoplanet 55 Cancri e compared to Earth.
“We used statistical analysis to determine the limits of possible compositions. Using a database of detected exoplanets, we have established that each theoretical planetary structure has a “threshold radius” beyond which there can be no planets of a certain composition,”explains Michael Lozovsky.
Promotional video:
An important factor in determining the threshold radius is the number of elements in the gaseous layer that are heavier than helium, the percentage of hydrogen and helium, and the distribution of elements in the atmosphere.
Super-Earths and Min-Neptuns
Researchers from the Institute of Computational Science have found that planets with a radius of less than 1.4 Earth's radius can be terrestrial, and exomers with a radius above this threshold contain a higher proportion of silicates or other lightweight materials. Most planets with a radius above 1.6 Earth's radius should have a layer of hydrogen gas or water in addition to their rocky core, while exoplanets 2.6 times Earth's size should not be water worlds and therefore can be surrounded by a dense atmosphere … Planets with radii greater than 4 Earth radii are expected to be gaseous and at least 10 percent hydrogen and helium, similar to Uranus and Neptune.
Exoplanets versus Earth, Mercury and Neptune.
The research results provide new insights into the development and diversity of exoplanets. A particularly interesting threshold concerns the difference between large earth-like planets, otherwise called super-Earths, and small gas planets, also called minineptuns. According to researchers, the border is 3 times the radius of the Earth. Thus, in the vast space of our Galaxy below this threshold, it is possible to find Earth-like planets without much difficulty.
