Also known as astrobiology, exobiology is the “study of life in space, combining aspects of astronomy, biology and geology. It is focused primarily on the study of the origin, distribution and evolution of life.
Some major astrobiological research topics include: What is life? How did life arise on Earth? What kind of environments can life tolerate? How can we determine if life exists on other planets? How often can we expect to find complex life? What will life consist of on other planets? Will it be DNA/Carbon based or based on something else? What will it look like?” <wiki> <“Meaning of Life“, SEED>
An estimate for the number of planets with (intelligent) extraterrestrial life can be gleaned from the Drake equation, essentially an equation expressing the probability of intelligent life as the product of factors such as the fraction of planets that might be habitable and the fraction of planets on which life might arise: