There isn't a single, established branch of science that specifically focuses on living organisms *outside* of Earth. This is because we haven't yet discovered any life beyond our planet.

However, there are several fields that *could* be involved in the study of extraterrestrial life if it were found:

* Astrobiology: This field studies the origin, evolution, and distribution of life in the universe. It combines elements of biology, astronomy, geology, and chemistry.

* Exobiology: This is a sub-field of astrobiology that focuses specifically on the search for life beyond Earth.

* Planetary science: This field studies planets and their moons, including their potential for supporting life.

* Space biology: This field investigates the effects of space travel and the space environment on living organisms.

So, while there isn't a single "extraterrestrial biology" field yet, the study of extraterrestrial life would draw upon a combination of these existing scientific disciplines.