The search for Earth 2.0 has begun in earnest. But there’s a huge variety of exoplanets out there, so narrowing down the search to focus valuable telescope time on only the best candidates is critical. One variable of a planet that will have a huge impact on its habitability is its size. A new paper, now available in pre-print on arXiv, by researchers at the University of California Riverside, looks into the impact of a planet’s size on one of its more critical features for habitability - whether it holds onto an atmosphere - and determines that slightly smaller than Earth is likely the smallest a planet can be and still be viable for life to develop.