BEIJING, June 16 (Xinhua) -- A group of researchers have found super-Earths (SEs) and mini-Neptunes (MNs) planets followed distinct evolutionary paths, after conducting an in-depth study based on large-sample observational data, according to the National Astronomical Observatories of the Chinese Academy of Sciences.
The findings of the study have been published in the journal Science, with the help of observational data from China's Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), Europe's Gaia satellite and the Kepler space telescope.
In the solar system, the four rocky planets of Mercury, Venus, Earth and Mars are distributed in the inner region, while the outer region is home to four gas and ice giants, Jupiter, Saturn, Uranus and Neptune.
Since the launch of the Kepler space telescope in 2009, astronomers have discovered thousands of exoplanets beyond the solar system, the vast majority of which have radii between those of Earth and Neptune.
These planets do not form a single and uniform group but instead fall into two categories: one is the SEs, which are slightly larger than Earth and composed mainly of rock and iron; the other is the MNs, which are larger in size and possess thick and gaseous envelopes.
The researchers said SEs are like the "survivors" in exoplanetary systems. They may have experienced violent processes such as gravitational scattering and giant impacts, which randomly excited their orbits to relatively high eccentricities, after which their orbits were rapidly circularized by tidal forces.
In contrast, MNs are like "natives" living in "quiet zones". They are dominated by gentle and long-term orbital evolution, with eccentricity slowly transferred from the outer to the inner regions, and rarely experience dramatic dynamical events.
"SEs and MNs may seem similar, but they have distinctly different 'personalities'," said Xie Jiwei, the corresponding author of the study. "Their orbital evolution history is crucial for understanding the formation and evolution of planetary systems." ■
