Dust is a predominant element in planetary systems and often represents the main source of light radiation after the central star. In the 1990s the question arose as to the possible presence of dust in newly-discovered extrasolar planetary systems and the possibility that this dust hindered the detection of other habitable planets, which is a major goal in 21^st century astronomy. For eight years, Olivier Absil and several French researchers studied some forty stars to try to determine whether they contained hot dust near or inside their habitable zone. Bottom line: the phenomenon is relatively common in solar-type systems.

This is a phenomenon that stargazers like to monitor: in the absence of artificial light (which is difficult on our planet…) or moonlight, it is possible to observe a cone of light rising on the horizon in the West just after twilight or in the East just before dawn. This phenomenon is called Zodiacal light because the cone appears along the Zodiac.

This diffuse light has been observed since ancient Egypt and its origin was explained in the 17^th century as solar light diffused by grains of interplanetary dust situated in the asteroid belt between Mars and Jupiter.

The composition of this cloud is not fixed however. Some grains exit the cloud and others enter it. It has been known for some years now that this cloud is continuously supplied with material from the evaporation of comets and the debris from collisions between asteroids. What interests Olivier Absil, who is the primary author of a study which has just appeared in Astronomy & Astrophysics (1) and a research associate at the FNRS in the Department of Astrophysics, Geophysics and Oceanography of the University of Liege, is the question of the possible presence of this cloud in newly-discovered extrasolar planetary systems and the fact that it possibly hinders the detection of other habitable planets. “What interests us, is to assess the presence of hot dust, which diffuses light close to the habitable zones around solar-type stars. These habitable zones can harbor exoplanets that are likely to have the necessary conditions for the development of life forms. This is very important because we know today that the presence of abundant amounts of hot dust can prevent the detection of planets, and even more so, the presence of biological activity on their surfaces. The detection of these extrasolar equivalents of the Zodiacal dust cloud represents an observational challenge because these dust populations are very close to the star and much less luminous than it, which tends to ‘dazzle’ the observation instrument”, explains the Liege-based researcher.

(1) « A near-infrared interferometric survey of debris discs stars : First statistics based on 42 stars observed with CHARA/FLUOR », Absil et al. 2013, A&A, 555, A104. www.aanda.org/10.1051/0004-6361/201321673