Are there life-sustaining planets revolving around other stars in the solar neighborhood?
Research during the latter half of this century has led to the development of a generally accepted concept of how stars and planetary systems form. The concept suggests that objects similar in mass and composition to Earth may exist in many, perhaps most, planetary systems. Detection of such planets is a key outcome of the search for planetary systems in general. However, in order to ascertain whether any of these planets may be life-sustaining, we need to be able to investigate the composition of their atmospheres. Liquid water is a basic requirement for life as we know it, and it is the key indicator that will be used to determine whether planets revolving around other stars may be life-sustaining. These issues will only be addressed when we have conducted a survey of a statistically significant number of nearby stars for the presence of planetary systems and observed them sufficiently to infer the masses and orbital properties of the planets in those systems.