NASA's proposed Early eVolution Explorer mission aims to solve the radius valley mystery

The proposed NASA Early eVolution eXplorer (EVE) mission, targeting the so-called "radius valley" among exoplanets, arrives at a pivotal moment in planetary science. The gap at roughly 1.8 Earth radii—where far fewer planets exist than predicted—has become a Rosetta Stone for understanding how worlds form and evolve. This feature isn’t merely a curiosity; it likely encodes the competing forces of stellar radiation stripping away atmospheres versus planetary cores resisting erosion. By focusing on young stars and their planetary embryos still embedded in gas disks, EVE could reveal whether photoevaporation, core-powered mass loss, or some hybrid mechanism carved the valley we see today. What makes the radius valley especially compelling is its connection to one of astronomy’s central questions: how common are worlds like our own? The gap’s precise location and slope vary with stellar type, hinting that the processes sculpting planets depend on factors like age, metallicity, and orbital distance. EVE would build on Kepler and TESS data by observing systems at ages where these mechanisms are actively shaping planets, potentially settling decades of debate. Yet its success hinges on instrumentation capable of teasing out atmospheric signatures in young, bloated worlds—a technical hurdle that mirrors the broader challenge of studying exoplanets in their infancy. The mission’s broader significance extends beyond the valley itself. If EVE confirms that early stellar radiation sculpts planetary populations, it would reinforce a paradigm where stellar environments—not just accretion physics—determine a planet’s fate. This would align with emerging evidence that the Milky Way’s planetary demographics are more diverse and dynamic than once assumed, with implications for habitability and the search for biosignatures. Open questions remain: Could the valley’s shape reveal whether gas giants migrate inward to trigger atmospheric loss? Do secondary atmospheres later fill the gap, creating "water worlds" in disguise? And how do these processes differ in star-forming regions with varying chemical abundances? As EVE awaits selection, its potential to rewrite planetary formation narratives underscores a larger trend: the shift from discovery to explanation in exoplanet science. The tools now emerging—from JWST to next-generation ground telescopes—are poised to turn statistical trends into physical laws, transforming our understanding of where, and how, worlds like Earth might arise.