Researchers at Cornell University have led an in-depth study into exoplanet KELT-9b popularly known as the ‘ultra-hot’ Jupiter in order to discover more about the exoplanet’s transmission spectrum. The study which was published in the journal of the American Astronomical Society was led by Jake Turner of Cornell University along with a team of scientists who discovered that the absorption lines along the exoplanet act as atmospheric ‘thermometers’.
Called as the ‘ultra-hot’ Jupiter, exoplanet KELT-9b clocks a dayside temperature of more than 4,500 K (~7,600 °F). It is the hottest planet known, hotter than many stars too! This ultra-hot Jupiter orbits at a mere 0.035 AU from its scalding A- or B-type host star in just 1.5 days.
Absorption lines act as atmospheric thermometers
The high temperature of this planet accompanied with intense radiation should dissociate molecules into their component atoms and ionize metals in the hot atmosphere. The energetic light should even inflate the envelope of hydrogen gas around the planet to the point where the hot gas escapes. However, for the second time, the presence of ionized calcium, Ca II, was discovered in KELT-9b’s atmospheric spectra along with a prominent Ha absorption, confirming the existence of an extended envelope of hydrogen surrounding the irradiated planet.
Turner and scientists were able to identify the pressures, altitudes, and temperatures of the lines in the atmosphere by modeling this atmospheric spectra. It was found that the Ca II lines probe the atmosphere at an altitude of about 1.32-1.40 times the planet’s radius. The Ha line provides information from higher up, at 1.44 planetary radii. Together, these absorption lines act as ‘atmospheric thermometers,’ providing an atmospheric temperature profile of the hottest planet and yielding insight into the energy that enters and leaves the planet’s atmosphere.