Rocky alien worlds may need to be young to support life

At this site, The Extrasolar Planets Encyclopaedia ( , there is 2343 exoplanets where radii <= 3 earth radii. Their semi-major axis range 0.0034 au to 1.98 au. This site, NASA Exoplanet Archive ( , there is 2667 exoplanets with radii <=3 earth radii size. Semi-major axis range 0.0058 au to 1.1218 au.

Models need to show if any of these exoplanets are habitable and earthlike I think now.

Reference paper cited, Mantle Degassing Lifetimes through Galactic Time and the Maximum Age Stagnant-lid Rocky Exoplanets Can Support Temperate Climates,, 03-May-2022. “Abstract The ideal exoplanets to search for life are those within a star's habitable zone. However, even within the habitable zone, planets can still develop uninhabitable climate states. Sustaining a temperate climate over geologic (∼gigayear) timescales requires a planet to contain sufficient internal energy to power a planetary-scale carbon cycle. A major component of a rocky planet's energy budget is the heat produced by the decay of radioactive elements, especially 40K, 232Th, 235U, and 238U. As the planet ages and these elements decay, this radiogenic energy source dwindles..."

My observation. In the reference paper cited, 17 exoplanets are noted in the study. "Table A2. Sample of Likely Solid Rocky Planets", table A2 lists some properties for these 17 exoplanets. TRAPPIST-1 f is the smallest mass listed, 1.039 earth mass, density 5.0 g cm^-3 with 7.6 Gyr age. The largest mass exoplanet on the table, Kepler-197 c, 5.3 earth mass, density 15.6 g cm^-3. The ages listed range 1.4 Gyr - 11 Gyr. Temperature is provided too in the table. 199 K - 1224 K. The first exoplanet on the table is K2-36 b,, a = 0.0223 au, P= 1.422614 day.

Searching for an earthlike exoplanet is very difficult and we have now more than 5,000 exoplanets confirmed to select from.

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