Titanium oxide detected in exoplanet atmosphere

In a first, astronomers including one of Indian-origin have detected small amounts of titanium oxide in the atmosphere of an extremely hot exoplanet.

Besides, titanium oxide, the atmosphere of the exoplanet WASP-19b contains small amounts water and traces of sodium, alongside a strongly scattering global haze, according to the study published in the journal Nature.

Titanium oxide is rarely seen on Earth although it is known to exist in the atmospheres of cool stars.

The exoplanet WASP-19b, which is about the same mass as Jupiter, is so close to its parent star that it completes an orbit in just 19 hours and its atmosphere is estimated to have a temperature of about 2,000 degrees Celsius.

“To be able to examine exoplanets at this level of detail is promising and very exciting,” said Nikku Madhusudhan from Cambridge University who oversaw the theoretical interpretation of the observations.

In the atmospheres of hot planets like WASP-19b, titanium oxide acts as a heat absorber.

If present in large enough quantities, these molecules prevent heat from entering or escaping through the atmosphere, leading to a thermal inversion the temperature is higher in the upper atmosphere and lower further down, the opposite of the normal situation.

Ozone plays a similar role in Earth’s atmosphere, where it causes inversion in the stratosphere.

“The presence of titanium oxide in the atmosphere of WASP-19b can have substantial effects on the atmospheric temperature structure and circulation,” Ryan MacDonald, an astronomer at Cambridge University, added.

As WASP-19b passes in front of its parent star, some of the starlight passes through the planet’s atmosphere and leaves subtle fingerprints in the light that eventually reaches Earth.

By using the observations from the Very Large Telescope, a facility operated by the European Southern Observatory (ESO) in Chile, the team was able to carefully analyse this light and deduce that the atmosphere contained small amounts of titanium oxide, water and traces of sodium, alongside a strongly scattering global haze.

“Detecting such molecules is, however, no simple feat,” explained Elyar Sedaghati, an ESO fellow.

“Not only do we need data of exceptional quality, but we also need to perform a sophisticated analysis. We used an algorithm that explores many millions of spectra spanning a wide range of chemical compositions, temperatures, and cloud or haze properties in order to draw our conclusions,” Sedaghati added.

The astronomers collected observations of WASP-19b over a period of more than one year.

By measuring the relative variations in the planet’s radius at different wavelengths of light that passed through the exoplanet’s atmosphere and comparing the observations to atmospheric models, they could extrapolate different properties, such as the chemical content, of the exoplanet’s atmosphere.

This new information about the presence of metal oxides like titanium oxide and other substances could allow much better modeling of exoplanet atmospheres.

Looking to the future, once astronomers are able to observe atmospheres of possibly habitable planets, the improved models would give them a much better idea of how to interpret those observations.

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