While Super-Earths and mini-Neptunes appear similar in size, their orbital histories followed radically different trajectories. Researchers in China have demonstrated that these two types of planets traveled down entirely separate evolutionary roads.
A team from the National Astronomical Observatory of the Chinese Academy of Sciences reached this conclusion after analyzing vast datasets from the LAMOST telescope, the Gaia satellite, and the Kepler space telescope. Their findings, published in the journal Science on June 17, 2026, reveal that Super-Earths—primarily composed of rock and iron—are the "survivors" of chaotic systems: their orbits initially became highly elongated due to gravitational disruptions and collisions before tidal forces rapidly smoothed them into circular paths.
In contrast, mini-Neptunes, characterized by their thick gaseous envelopes, underwent a much more stable development. Their orbits evolved slowly and steadily without dramatic interference, as eccentricity was gradually transferred from the outer reaches of the system inward. "Super-Earths and mini-Neptunes may seem alike, but they possess entirely different 'personalities'," explained Xia Jiwei, the study’s corresponding author.
This discovery reshapes our understanding of how planetary systems form, proving that worlds with similar radii do not always share a common origin. The dynamic history of a planet's orbit is now seen as the critical factor in determining how these worlds were born and how they endured.
By utilizing data from LAMOST, Gaia, and Kepler, the researchers were able to distinguish between the two populations based on the relationship between their orbital periods and eccentricities. This study provides the first statistically reliable evidence of their independent developmental trajectories.
