A proposed NASA mission called the Early eVolution Explorer (EVE) seeks to resolve a decade-old puzzle in planetary science: the 'radius valley' that divides exoplanets into two distinct size categories. The concept, detailed in a draft pre-print on arXiv, targets the gap at roughly 1.8 Earth radii where planets are unexpectedly scarce.
The radius valley separates smaller 'super Earths' with rocky interiors from larger, puffier 'sub-Neptunes.' Scientists debate what mechanism in planetary evolution forces this bifurcation — whether atmospheric loss, core composition, or formation history explains the divide. EVE would observe young exoplanets to capture them before they settle into these categories.
As a proposed mission, EVE is still in the concept phase with no confirmed launch date or budget. The draft outlines observational strategies focused on stars with known planet populations to track how interiors and atmospheres develop over time. Past surveys like Kepler and TESS have mapped the valley's existence but not its cause.
If selected, EVE could reshape understanding of planetary habitability by revealing why some worlds remain rocky while others grow thick atmospheres. The mission would compete with other Discovery-class proposals, each targeting different astrophysical questions within cost and timeline constraints.
Critics argue that existing telescopes like the James Webb Space Telescope already offer glimpses into young exoplanet atmospheres, potentially making a dedicated EVE mission redundant. Proponents counter that EVE's targeted survey design would provide the statistical sample necessary to confirm causal mechanisms rather than circumstantial evidence.