The term exobiology describes the science of finding life beyond our planet Earth. Exobiology is in fact a more specific area of astrobiology – the two fields of science are very closely linked together.
A brief introduction
Astrobiology is the study of the origin and evolution, distribution and future of life in the universe whereas exobiology covers the searching part of life beyond Earth and the effects of extraterrestrial environments on living things.
Astrobiology and exobiology can be considered as the links between life and the universe. Simply put, astrobiology is where the scientific observation techniques meet biology and chemistry.
Methods used in exobiology
A variety of methods in exobiology are used to find and evaluate the possibility of life outside of our planet. The most important aspect deals with astronomy – the techniques applied to find a suitable planet to support life as we know it.
The basics exobiology
The mainstream informed assumption is that the vast majority of life forms in our galaxy are based around carbon chemistry. Majority of the search for extraterrestrial life is focused on this assumption.
Carbon is well known for the unusually wide variety of molecules that can be formed around it. Carbon is also the fourth most abundant element in the universe and it has the ability to build a wide variety of stable yet reactive molecules.
Another very important aspect of a planet’s habitability is considered to be the presence of liquid water. Water – in combination with carbon based molecules – provides excellent environment for the formation of complicated chemical structures that could eventually lead to the emergence of life. Aside from carbon, some researchers also pose that water-ammonia based environments could serve as a base for more hypotethical types of biochemistry.
A key factor is also considered to be that the planet would be roughly the same size and composition with our Earth.
The third assumption is keeping focus on exoplanets that orbit Sun-like stars to increase the probability of finding a habitable planet. There are two main reasons why medium-sized stars like our Sun are considered the best for harboring habitable planets.
Very large stars have relatively short lifetimes, which means that life might not simply have enough time to develop on planets that orbit them. On the other hand, very small stars provide too little warmth that only planets very close to the sun would not be frozen solid.
The properties described above can be analyzed using satellites launched into space. Spectroscopic methods are used to to study the spectrum of a planet’s atmosphere while it’s passing over the star it’s orbiting, revealing the atmospheric properties of the planet studied. By observing how much of the star’s light the studied planet blocks, the size of the planet can be determined. The gravitational effects on the planet’s star give away the planet’s mass.
So far Earth is the only planet known to harbor life. Therefore there is no certain way to know whether or not any of these simplifying assumptions are correct.
Missions aiming to find extraterrestrial life
Numerous missions have been launched by NASA and ESA to benefit the discovery of life beyond earth. Most notable missions attempting to find Earth-sized exoplanets are NASA’s Terrestrial Planet Finder (TPF) and ESA’s Darwin programs. Both of the programs have now been cancelled. NASA has launched the Kepler mission in March 2009 and the French Space Agency launched the COROT space mission in 2006.
The purpose of these missions is not only to detect Earth-sized planets, but also to detect light from the planet so that it may be studied using spectroscopy. NASA is also running a research group called Virtual Planet Laboratory, which uses computer modeling to generate a wide variety of virtual planets to see what they would look like if they were viewed by TPF or Darwin.
There’s also an equation called the Drake Equation that can be used to estimate the probability for the number of planets harboring intelligent, communicating extraterrestrial life.
Due to the vastness of our universe, currently the available technology allows us to only study planets within our galaxy. Studying the possibility of life in the billions of other galaxies will