## new Research Suggests Many ‘Mini-Neptunes’ May Have Solid Surfaces
Recent findings challenge the prevailing understanding of “mini-Neptunes,” a common type of exoplanet, suggesting many may not be the molten lava worlds previously theorized. A team of researchers, including scientists from the University of Chicago, have discovered evidence indicating these planets could possess solid, rocky surfaces.
For years, astronomers have relied on indirect methods – like observing dips in starlight as planets transit their stars, analyzing atmospheric light, and measuring gravitational influences – to study exoplanets. These observations revealed a surprising abundance of mini-Neptunes around other stars, a stark contrast to the absence of such planets in our own solar system.
Initial assumptions pointed to extremely high temperatures and dense atmospheres resulting in global oceans of molten magma on these planets,mirroring Earth’s early state. UChicago Associate Professor Edwin Kite previously theorized that these magma oceans could even consume their own atmospheres, limiting planetary growth.
Though, a closer examination of data, particularly concerning the planet GJ 1214 b in the constellation Ophiucus, prompted a re-evaluation. New data from the James Webb Space Telescope indicates GJ 1214 b’s atmosphere contains molecules larger than hydrogen and helium, suggesting a substantially heavier atmosphere than previously estimated.
This heavier atmosphere would create immense pressure. Researchers found the pressure could be so intense that the rock beneath would transition from molten magma *back* into solid rock, similar to how carbon forms diamonds deep within Earth.
Led by Bodie Breza, the first author of the study, and including researchers Matthew Nixon (now a 51 Pegasi b postdoctoral fellow at Arizona State University) and Kempton, the team conducted simulations with varying planetary conditions. These simulations revealed that a substantial number of mini-Neptunes previously classified as lava worlds may, actually, have solid surfaces.
“It’s an either-or,” explained Kempton. “You can have this the-floor-is-lava scenario, or a solid surface, and you’re going to have to take into account a number of other factors about a planet’s atmosphere to try to figure out which regime it falls under.”
The prevalence of mini-Neptunes is particularly intriguing to scientists as it challenges established theories of planetary formation. ”before we found any exoplanets, we had a nice neat story about how solar systems form based on how our solar system formed,” said Nixon. “We thought that would apply to other solar systems… But they don’t.”
Understanding the formation and current state of mini-Neptunes is crucial for developing a more thorough understanding of planet formation in general, and ultimately, for guiding the search for habitable planets. As Nixon stated, “This is a really fundamental piece for us to understand both other planets and our own.”
The research was published in *Astrophysical Journal Letters* (https://doi.org/10.3847/2041-8213/ae0c07).
