New "Mars Similarity Index" Broadens the Search for Life Beyond Earth-Analog Planets

An April 2026 arXiv preprint (2604.06792v1) introduces the Mars Similarity Index, which rates exoplanet habitability against Mars rather than Earth. The metric targets planets where extremophile life could persist in thin-atmosphere, high-UV conditions. It argues that limiting habitability assessments to Earth analogs may overlook environments where life could exist in forms quite different from our biosphere.