Astronomers have directly detected a planet in a triple star system using imaging techniques. The planet's peculiar arrangement between three stars as well as its wide orbit within the multi-star system expand current models of how star systems and their planets form. To date, detecting exoplanets in multi-star systems has proven challenging, meaning that most directly imaged exoplanets have been detected around single stars, and less so around binary stars. Here, a relatively young triple star system, called HD 131399, was observed by Kevin Wagner and colleagues using the Very Large Telescope (VLT) and the Spectro-Polarimetric High-Contrast Exoplanet Research instrument (SPHERE). Within the system, a gas giant planet roughly four times the size of Jupiter, containing water and methane, was detected. The planet, HD 131399Ab, appears to have a very wide orbit around one of the stars, with the other two stars orbiting outside, which is highly unusual. The authors propose several ways in which HD 131399Ab may have come into its unique orbit, including the possibility that it once circled two stars and underwent a scattering event via interactions with another planet, or with its binary stars. Further study of this mysterious system may shed light on how planets form and change orbit.
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Journal
Science