Atmosphere – a ghost by the world of glass rains

Scientists from the Institute of Laser Physics of the Siberian Branch of the RAS have modelled atmosphere of the well-known “hot Jupiter” HD 189733b and found out what hindered from stable finding of hydrogen in the atmosphere of the planet. They also defined physico-chemical properties of this planetary system. They told about it at the symposium of Asian Pacific Geophysical Society in August 2023, the preliminary publication was made in The Astrophysical Journal.

Exoplanets are planets beyond Solar system. The most studied of them are from the family of so called hot Jupiters. They can be compared with Jupiterian ones as far as size and weight is concerned, but orbit to their stars 10 times nearer that Mercury to the Sun. Such close distance and high temperatures make atmosphere to escape from planets with ultrasound speed, and the movement of the atmosphere, and also its content, can be studied with the help of method of transit spectroscopy. This method consists in registration of absorptions of stellar radiation by planet’s atmosphere and enables to make through-transmission definition of which elements are present in the atmosphere, and make conclusions about speed and density of various elements.

HD 189733b has attracted researchers and observation time of telescopes for not one decade. The planet became popular due its blue color, caused by glass (silicate) rains – particles of silicates, raised into the atmosphere. One of the most interesting mysteries of this planet was “disappearing” transit in hydrogen line Lya – measurements of absorptions in this diapason of wave length turned out to be rather inconsistent. A bit better is the situation with IK -line of metastable helium 1083 nm – transit in its locality was observed twice, but with different amplitude. Such changes tell about substantially different regimes of outflow of planetary matter HD 189733b, and computer modelling is the most available way of checking out possible causes of changes.

One of the most advanced instruments for modelling of complex of features in the atmosphere of exoplanets and interpretation of transit absorptions in the world was created and is developed by scientists from the Institute of Laser Physics of the Siberian Branch of the RAS. Having applied it to HD 189733b, scientists found out that the most probable cause of unstable absorptions in hydrogen line Lya is high activity of host star, that appears in increasing of radiation flux in ultraviolet area (FXUV, erg∙cm-2с-1Å-1 for 1 АЕ) and speed of losing of mass of stellar material. It turned out that changes in those factors can cause not only variable detections of transit absorption in hydrogen line due to formation of energetically neutral atoms in strong stellar wind but also different absorptions in the line of metastable helium.

The material was prepared with the financial support of the Russian Ministry of Education and Science within the framework of the federal project “Popularization of science and technology”.