SPL RF Jun 2021

HD 209458 is a star with an extrasolar planet. The planet, HD 209458b or Osiris, orbits so close to its parent star (only a few stellar diameters away) that star's stellar wind is gradually stripping away the planet's atmosphere, to form a long, comet-like tail that stretches into space. In 2021, astronomers led by the University of Warwick discovered chemical signatures in the atmosphere of the planet as it passed in front of its star (a transit). The research concluded that the planet likely formed much farther from its host star, but later migrated inward to its current position. The illuminated crescent and its colours have been exaggerated to illustrate the light spectra that the astronomers used to identify the six molecules in its atmosphere.