Space telescopes and ground-based telescopes have been discovering a wide variety of exoplanets in the last few decades - several thousand have been found so far and the estimated total number is in the billions in our galaxy alone. Now, astronomers have found the first exoplanet with titanium oxide in its atmosphere. The chemical compound is rare on Earth but can be found in the atmosphere of some cooler stars.
The planet, a hot-Jupiter called WASP-19b, was observed with the FORS2 instrument on the Very Large Telescope at the European Southern Observatory (ESO) for over one year. It has a similar mass to Jupiter, but orbits its star in only 19 hours. By analyzing the composition of the planet's atmosphere, estimated to be 2,000 degrees Celsius, astronomers discovered small amounts of titanium oxide, water and traces of sodium, along with a strongly scattering global haze. The team studied variations in the radius of the planet at different light wavelengths. They then compared those to known atmospheric models, in order to examine different properties of the planet's atmosphere.
“Detecting such molecules is, however, no simple feat,” said Elyar Sedaghati of ESO. “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.”
As noted by Ryan MacDonald, team member and astronomer at Cambridge University, United Kingdom, “The presence of titanium oxide in the atmosphere of WASP-19b can have substantial effects on the atmospheric temperature structure and circulation.”
Path of stellar light through the atmosphere of WASP-19b
"To be able to examine exoplanets at this level of detail is promising and very exciting.” said Nikku Madhusudhan, also from Cambridge University.
Titanium oxide is very rare on Earth, but can be found in the atmospheres of cool stars. On such planets it is thought that it could create thermal inversions, where the temperature is higher in the upper atmosphere and lower further down near the surface. This is of course opposite from what we are familiar with on Earth, although ozone creates a similar effect high up in the stratosphere.
Although this is only the first exoplanet where titanium oxide has been found so far, the results will aid astronomers in the study of other exoplanets, hot-Jupiters in particular. Our own Solar System does not have any similar hot-Jupiter type planets, but they have been discovered orbiting a growing number of other stars. They are gas giant planets, orbiting very close to their stars and are searingly hot, hence the name. Many are also larger than Jupiter. Jupiter and Saturn, the two gas giants in our Solar System, are much farther out and much colder. The ice giants, Uranus and Neptune, are colder still. Since hot-Jupiters now seem to be fairly common, scientists are curious as to why there are none in our Solar System. Figuring this out would also provide more clues as to how our own planetary system formed and evolved.
In the near future, astronomers will also be able to better analyze the atmospheres of smaller rocky exoplanets like Earth, in the search for evidence of alien life. While hot-Jupiters are certainly not life-friendly, the improving ability to study their atmospheres is a big step in that direction.
“This important discovery is the outcome of a refurbishment of the FORS2 instrument that was done exactly for this purpose,” said team member Henri Boffin from ESO. “Since then, FORS2 has become the best instrument to perform this kind of study from the ground.”
The new study has been published in the journal Nature.