Background of the radius valley
For more than ten years, planetary scientists have noted a pronounced gap in the distribution of exoplanet sizes. Objects with radii around 1.8 times that of Earth appear far less frequently than expected, despite the rapid growth in discovered worlds.
Current classification of exoplanets
Most known exoplanets fall into two categories. Below the gap are compact, rocky bodies often called “super‑Earths.” Above the gap lie larger, low‑density planets referred to as “sub‑Neptunes,” which retain substantial gaseous envelopes.
Purpose of the Early eVolution Explorer
The NASA‑proposed Early eVolution Explorer (EVE) intends to use high‑precision measurements of planet radii and densities to uncover the processes that create the observed deficit. A concept paper posted on arXiv outlines a dedicated space telescope designed to probe atmospheric composition and mass‑radius relationships of selected targets.
Approach and expected outcomes
- Transit photometry to derive accurate planetary radii.
- Spectroscopic analysis of atmospheres to assess composition and possible atmospheric loss.
- Statistical study of a large sample to reveal evolutionary trends.
By contrasting data from both sides of the radius valley, researchers hope to pinpoint the physical mechanisms that drive the transition from rocky to gas‑rich worlds.