Wednesday, June 22, 2022

Osiris, a giant exoplanet

5:39 PM |

HD 209458b is a complex name that hardly remains imprinted in memory. For this reason this exoplanet with such particular characteristics has been nicknamed with the evocative name of Osiris.

Osiris is a gas giant with a mass 0.65 times that of Jupiter orbiting a yellow dwarf similar to the Sun 150 light years from Earth.

Unlike the gas giants of the Solar System, Osiris moves on an orbit with a semi-major axis of just 0.047 AU, 1/8 of the Sun-Mercury distance, and thus completes a revolution around its star in just 3.5 days. This means that the surface temperature of the planet is very high, above 1000 K, which makes it a typical warm Jovian planet.

So far nothing special, are in fact known hundreds of gas giants that are in close orbit around their star. What makes Osiris noteworthy is that it was the first exoplanet from which spectroscopic observations of the Hubble Telescope were able to determine atmospheric composition. It has been discovered that the planet’s atmosphere is composed mainly of hydrogen, with important percentages of oxygen and carbon and traces of water vapor. The excessive proximity to the star, however, means that atmospheric gases are torn away from the planet due to the intense stellar wind and are dragged into space forming a long gas tail, which may appear similar to that of this artistic representation. It is therefore possible that in the future Osiris is completely stripped of its atmosphere and that only its rocky core remains.

Credit: ESA, NASA.

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