## new Research Suggests Many ‘Mini-Neptunes’ May Have Solidโ Surfaces
Recent findings challenge โthe prevailing understanding โof “mini-Neptunes,” a common type of exoplanet, suggestingโค many mayโข not be the molten โคlava worlds previously theorized. A team of researchers, including scientists fromโ the University of Chicago, have discovered evidence indicating these planets could possess solid, rocky surfaces.
For years, astronomers have โฃrelied on indirect methods – likeโค observing dips in starlight as planets transitโ their stars, analyzingโข atmospheric light, and measuring gravitational influences – toโข study exoplanets. These observations revealedโ a surprising abundance of mini-Neptunes around โฃotherโข stars, aโ stark contrast to the absenceโ of such planets in our own โsolar system.
Initial โคassumptions pointed to extremely high temperatures and dense โคatmospheres โresulting inโ global oceansโฃ of molten magma on these planets,mirroring Earth’s early state. UChicago Associateโข Professor Edwin Kite previously theorizedโข that these โmagma oceans could evenโข consume their own atmospheres, limiting planetary growth.
Though,โข aโค closer examination of data, particularly โคconcerning the โคplanetโ GJ 1214 b in the constellation โฃOphiucus, prompted aโข re-evaluation. New data from โฃthe James Webbโ Space Telescope indicates GJ 1214 โb’s atmosphere contains molecules larger than hydrogenโข and helium, suggesting a substantially heavier atmosphere than previously estimated.
This heavierโ atmosphere would create immense โpressure. Researchers found the โpressure could be so intense that the rockโค beneath โคwould transition from molten magma *back* โinto solid rock, similar to howโข carbon forms diamonds deep within Earth.
Led by Bodie Breza, the first author of the study, and โincluding researchers Matthewโข Nixon (now a 51 Pegasi b postdoctoral fellow at Arizona State University) andโ Kempton,โค the team conducted simulations with varying planetary conditions. โฃThese simulations revealedโ that a substantial โคnumber of mini-Neptunes previously classified as lava worlds may, actually, have solid surfaces.
“It’s โan either-or,”โ explained Kempton. “You can have โthis the-floor-is-lava scenario, or a โsolid surface, and you’re going to have to take into account a number of other factors about โa planet’s โatmosphere to try to figure out which regime โฃit falls under.”
The prevalence of mini-Neptunes is particularly intriguing to scientists as it challenges established theories of planetary formation. โ”before we found any exoplanets, we had a nice neat story โabout how solar systems form basedโ on how our solar system formed,” said Nixon. “We thought that would apply to other solar systemsโฆ But theyโฃ don’t.”
Understanding the formation and current state of โmini-Neptunes is crucial for developing a โmore thorough โคunderstanding of planet formation in general, โand ultimately, for guiding the search for โhabitable planets. As Nixon stated, “This is a really fundamental โคpiece for us to understand โคboth otherโข planets andโข our โคown.”
Theโข research was โคpublished in *Astrophysical Journal Letters* (https://doi.org/10.3847/2041-8213/ae0c07).
