VLT makes first detection of titanium oxide in an exoplanet

An artist’s impression showing the exoplanet WASP-19b, in
which atmosphere astronomers detected titanium oxide for the
first time. In large enough quantities, titanium oxide can
prevent heat from entering or escaping an atmosphere, leading
to a thermal inversion — the temperature is higher in the
upper atmosphere and lower further down, the opposite of the
normal situation. Credit: ESO/M. Kornmesser

A team of astronomers led by Elyar Sedaghati, an ESO fellow
and recent graduate of TU Berlin, has examined the atmosphere
of the exoplanet [WASP-19b] in greater detail than ever
before. This remarkable planet 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 2000 degrees Celsius.

As WASP-19b passes in front of its , some of the starlight passes through
the planet’s and leaves subtle
fingerprints in the light that eventually reaches Earth. By
using the FORS2 instrument on the Very Large Telescope 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,”
explains Elyar Sedaghati, who spent 2 years as ESO student to
work on this project. “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.”

Titanium oxide is rarely seen on Earth. It is known to exist in
the atmospheres of cool stars. In the atmospheres of hot
planets like WASP-19b, it 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 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.” explains Ryan MacDonald, another
team member and an astronomer at Cambridge University, United
Kingdom. “To be able to examine exoplanets at this level of
detail is promising and very exciting.” adds Nikku Madhusudhan
from Cambridge University who oversaw the theoretical
interpretation of the observations.

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

“This important discovery is the outcome of a refurbishment of
the FORS2 instrument that was done exactly for this purpose,”
adds team member Henri Boffin, from ESO, who led the
refurbishment project. “Since then, FORS2 has become the best
instrument to perform this kind of study from the ground.”

This research was presented in the paper entitled “Detection of
in the atmosphere of a hot
Jupiter” by Elyar Sedaghati et. al. to appear in Nature.

Explore further:

Hubble detects exoplanet with glowing water atmosphere

More information: Detection of titanium oxide in the
atmosphere of a hot Jupiter, Nature (2017). nature.com/articles/doi:10.1038/nature23651

Journal reference: Nature

Provided by: ESO