Scientists, including one of Indian origin, have detected titanium oxide in the atmosphere of a Jupiter-like hot exoplanet for the first time. The results, reported in the journal Nature, provide unique information about the chemical composition and the temperature and pressure structure of the atmosphere of this unusual and very hot world.
The planet, WASP-19b, has about the same mass as Jupiter, but 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. Such planets are known as 'hot Jupiters'.
As WASP-19b passes in front of its parent star, some of the starlight passes through the planet's atmosphere and leaves subtle molecular fingerprints in the light that eventually reaches Earth.
"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," said Elyar Sedaghati, from the European Southern Observatory (ESO) in Germany.
Using the FORS2 instrument on the ESO's Very Large Telescope 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.
"Titanium oxide can substantially affect the behaviour of WASP-19b's atmosphere," said Ryan MacDonald, a PhD student at University of Cambridge in the UK.
"From altering its temperature structure, to driving strong winds, we are now one step closer to uncovering the nature of this extreme world," said MacDonald.
Titanium oxide (TiO) is rarely seen on Earth, but it in the atmospheres of hot planets like WASP-19b, it can absorb the incoming starlight in the same way that ozone absorbs the incoming sunlight in the Earth's stratosphere.
This causes a temperature inversion in the stratosphere whereby temperature increases with altitude. The energy from the absorbed starlight higher up in the atmosphere is released locally and causes the temperature to be higher in the upper atmosphere and lower further down, the opposite of the normal situation.
"TiO has been predicted to exist in hot Jupiters for over a decade but its conclusive detection has proved elusive in the past," said Nikku Madhusudhan of Cambridge's Institute of Astronomy, who oversaw the atmospheric analyses.
"The clear detection of the molecule is a major observational advancement it is an exciting time in exoplanetary science," said Madhusudhan.
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 titanium oxide and other metal oxides will allow a deeper understanding of the chemical and physical processes in exoplanetary atmospheres.
