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We review the latest findings on extra-solar planets and their potential tosupport Earth-like life. Focusing on planets orbiting Red Dwarf (RD) stars, themost abundant stellar type, we show that including RDs as potential host starscould increase the probability of finding biotic planets by a factor of up to athousand, and reduce the estimate of the distance to our nearest bioticneighbor by up to 10. We argue that binary and multiple star systems need to betaken into account when discussing exoplanet habitability. Early considerationsindicated that conditions on RD planets would be inimical to life, as theirHabitable Zones (where liquid water could exist) would be so close as to makeplanets tidally locked to their star. This was thought to cause an erraticclimate and expose life forms to flares of ionizing radiation. Recentcalculations show that these negative factors are less severe than originallythought. It has been argued that the lesser photon energy of the radiation ofthe relatively cool RDs would not suffice for Oxygenic Photosynthesis (OP) andother related energy expending reactions. Numerous authors suggest that OP onRD planets may evolve to utilize photons in the infrared. We however argue, byanalogy to the evolution of OP and the environmental physiology anddistribution of land-based vegetation on Earth, that the evolutionary pressureto utilize infrared radiation would be small. This is because vegetation on RDplanets could enjoy continuous illumination of moderate intensity, containing asignificant component of photosynthetic 400-700 nm radiation. We conclude thatconditions for OP could exist on RD planets and consequently the evolution ofcomplex life might be possible. Furthermore, the huge number and the longlifetime of RDs make it more likely to find planets with photosynthesis andlife around RDs than around solar type stars.

The Potential of Planets Orbiting Red Dwarf Stars to Support Oxygenic Photosynthesis and Complex Life