The search for life on exoplanets takes a fairly conservative approach. It focuses on life that is similar to that of Earth.
Sure, it’s quite possible that life comes in many exotic forms, and scientists have speculated about all the strange forms life might take, but the simple fact is that Earth life is the only form we currently understand. So most research focuses on life forms that, like us, are carbon-based with biology that relies on liquid water.
But even with that narrow view, life could still be hiding in places we don’t expect.
Since terrestrial life depends on liquid water, the search for life on exoplanets focuses on those within the circumstellar habitable zone (CHZ) surrounding stars. That is, not too close nor too distant so that liquid water could exist on a rocky planet.
For our solar system that’s roughly between the orbits of Venus and Mars. Most of the exoplanets meeting that criteria are super-Earths that closely orbit small red dwarf stars, since red dwarfs make up about 75% of the stars in our galaxy, and super-Earths are the most common terrestrial exoplanet.
One of the surprising discoveries about exoplanets is that Jupiter-sized planets often orbit close to their stars. These “hot Jupiters” aren’t likely to have life, but they could have moons that are as warm and wet as Earth.
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