Free Astronomy Magazine September-October 2014

EXOPLANETS studies on the dynamic and physical prop- erties of the entire system, including GJ 581. The astronomers involved in those re- searches soon however realized that some- thing was not completely right, because the results were often conflicting with each other and each new planet discovered seem- ed to change things around again. The most notable case in this respect is the dis- covery of GJ 581e, the innermost of all (with a period of 3.15 days), which required an adjustment to be made to the period of GJ 581d from 82 to 66 days, so as to make it all tally up. It must also be added that it is precisely from the orbital properties of planet “d”, in particular from the value of the inclination adopted, that the existence of planet “g” has always depended (for which a period of 33 days had been esti- mated). This without mentioning planet “f”, the outermost of all, with an estimated pe- riod of 433 days, whose existence has been repeatedly questioned, so much so that for some time now is considered an error resulted from the procedures adopted –at the time of its discovery– to investigate that planetary system. Planets “d” and “g”, instead, have had sup- porters until a few months ago, when they too had to throw in the towel after the re- sults produced by the team of the Penn State University –namely Paul Robertson, Suvrath Mahadevan, Michael Endl and Ar- pita Roy– were published in Science in July. To permanently solve the issue of the phan- tom planets of GJ 581, the researchers used the same material that enabled their dis- covery, in addition to other material which had already previously undermined the soundness of some of the findings. That material consists of 239 spectra of the red dwarf obtained with two of the best spec- T his is how the diagram com- paring our solar system (as far as Jupiter) with that of Gliese 581 has been updated. Planets g, d and f have never exist- ed. [F. Selsis/ESO]