Inverted Inferno

A paradox world in a distant star system.

The mysterious world of exoplanets continues to get stranger, with the first ever discovery of titanium oxide in a planetary atmosphere outside our Solar System. The unusual properties of the molecule means that it can absorb heat, not allowing it to escape, leading to the outer regions of the distant world likely being, paradoxically, hotter than its core.

The scorching, Jupiter-mass world — officially dubbed WASP-19b — was extensively studied by astronomers, in a team led by a fellow at the European Southern Observatory in Germany, Elyar Sedaghati. By using the specialist instrument FORS2, one of many on ESO’s Very Large Telescope in Chile, the tiny trickle of light from the planet’s host star that passes through the planet’s atmosphere on its way to Earth was detected and analysed.

This analysis — a process known as spectroscopy — allowed the astronomers to determine which chemicals were present in the planet’s atmosphere. Because exoplanets lie at such great distances from Earth, the team required extremely high quality data to pick out the individual chemicals, and so observed three transits of WASP-19b passing in front of its host star, over the course of more than a year.

To bolster the technique, the team took observations of the planet in several different wavelengths of light, and looked at how the planet’s radius appeared to change between each. Together with the use of specialist algorithms and comparisons with existing atmospheric models, the chemical signatures in the collected light were painstakingly teased out. Along with some common molecules, such as water and sodium, the team made the record books by picking up the traces of titanium oxide, a molecule rarely seen on Earth.

Similar to the way ozone behaves in the atmosphere of our own planet, titanium oxide on WASP-19b traps and holds on to thermal energy, leading to a warming of the atmospheric layer where the chemical is present. Coupled with its very close orbit around its parent star — one of the shortest known at just 19 hours — the planet’s atmosphere is estimated to be around 2000 degrees Celsius.

Brand new discoveries like these continue to give clues about exoplanets and provide astronomers with more pieces of the puzzle in understanding their compositions. With this new information, about substances such as metal oxides, more accurate atmospheric models can be devised. Equipped with these improved models, astronomers who are searching for potentially habitable worlds in the future will have a much better idea of how to interpret the light collected from them, assisting in the search for life.

Image: M. Kornmesser/ESO

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