The quest for planets outside the Solar System is one of the most exciting fields of astronomy in the last decade. Planets are virtually impossible to detect directly, due to the very weak radiation they emit, compared to their host stars. Instead, astronomers look for the minute motion of the host star around the center of mass of the star-planet system. In order to detect this motion, they measure the Doppler effect on the stellar spectrum. Using this technique, the stellar velocity can be measured to a precision of a few meters per second, which is enough to detect motions caused by the presence of planets. The article describes one of the latest discoveries – the system HD41004. This system comprises a double star, a planet orbiting the brighter companion, and a brown dwarf orbiting the fainter companion. A brown dwarf is a stellar object which is too small to ignite the thermonuclear processes which are responsible for the energy emission in stars.

The detection is the result of a collaboration between a Swiss team and an Israeli team (the authors).  The observations were carried out by the swiss, who also noted the velocity fluctuations. The Israelis used a software they developed to separate the light from the two stellar components and characterize the two smaller objects. The peculiarity of HD41004 and similar systems may shed more light on the creation and evolution of stars, brown dwarfs and planets, and especially the creation of our own Solar System.