A new study from Rice University is giving scientists fresh hope that more Earth-like planets may exist in the universe.
Researchers Sho Shibata and Andre Izidoro created a new model that explains how two of the most common types of planets—super-Earths and mini-Neptunes—form.
These planets are between one and four times the size of Earth and are found throughout our galaxy.
The study, published in The Astrophysical Journal Letters, challenges old ideas about how these planets are made.
Instead of forming from scattered bits of space dust across wide areas, the researchers believe planets form in narrow rings of material around young stars.
These rings help organize the building blocks of planets, making their formation more structured than previously believed.
“This model is important because it helps us understand how the most common planets in our galaxy come to be,” said Shibata, a postdoctoral researcher in planetary sciences.
To test their theory, the team used powerful computer simulations called N-body models. These simulations show how tiny space rocks called planetesimals collide and grow into larger bodies over millions of years. The researchers focused on two zones in the disk around a star: one close to the star (within 1.5 times the distance between the Earth and the Sun) and another farther out, near the “snow line” where water can freeze.
Their results showed that super-Earths tend to form closer to the star through solid material collisions, while mini-Neptunes form farther out by collecting icy pebbles. This explains why some planets are rocky and smaller, and others are larger and covered in gas or water.
One key finding explains something scientists call the “radius valley.” This refers to a gap in planet sizes: there are fewer planets around 1.8 times the size of Earth. The model shows this gap naturally forms because planets smaller than 1.8 Earth radii are mostly rocky, while larger ones have thick atmospheres or water layers.
Another interesting outcome is the “peas-in-a-pod” pattern—when planets in the same system are similar in size. The ring model explains this too, since planets forming in the same ring end up growing in similar ways.
Even more exciting, the model suggests that some Earth-like planets could form in the habitable zone—the region around a star where temperatures could allow liquid water. Although rare, the researchers estimate that about 1 in 300 Sun-like stars might host such a planet.
With future space telescopes, scientists hope to test these predictions. If they hold true, this new model could change our entire understanding of how planets form across the universe—and how many might be like Earth.
Source: Rice University.
