Over the last few years, intensified research and improved observational techniques have led to the discovery of stars which are orbited by companions of very low mass. The data so far available indicate that at least the majority of these have masses comparable to that of Jupiter, the largest planet in our own solar system. None of the companions discovered so far has, however, yet been observed directly. It is therefore conceivable that a few candidates might yet turn out to be stars too small to ignite hydrogen burning in their interiors, so-called brown dwarfs. Efforts to discover more planetary companions to other stars in the Milky Way galaxy are being vigorously pursued and will no doubt feature prominently in astronomical research over the next several decades.
The IAU, through its Division III: Planetary Systems Sciences, provides a forum for international discussion and coordination of research in this exciting new branch of astronomy. The next major opportunity for an in-depth review of the field will be IAU Symposium No. 202, Planetary Systems in the Universe, at the 24th IAU General Assembly. Ongoing work under the auspices of the IAU will focus on the reliability and complementarity of the several techniques used to detect and characterise extra-solar planets. As the number of confirmed cases increases, astronomers will begin to better understand how planetary systems, including our own solar system, form and evolve.
In order to facilitate international research in the field, and as part of these discussions, the IAU is also developing a system for clear and unambiguous scientific designation of these bodies at all stages during their study, from tentative identification to fully-characterised objects. Such a system must take into account that discoveries are often tentative, later to be confirmed or rejected, possibly by several different methods, and that several planets belonging to the same star may eventually be discovered, again possibly by different means. Thus, considerable care and experience are required in its design.
In response to frequent questions about plans to assign actual names to extra-solar planets, the IAU sees no need and has no plan to assign names to these objects at the present stage of our knowledge. Indeed, if planets are found to occur very frequently in the Universe, a system of individual names for planets might well rapidly be found equally impracticable as it is for stars, as planet discoveries progress.