A team of researchers from different institutions in the United Kingdom and USA coordinated by experts from the Pennsylvania State University has discovered an extrasolar planet in which it snows titanium dioxide, one of the main compounds of sunscreens. The data provided by the Hubble Space Telescope have allowed determining that these precipitations only take place in a region of this object in which it is permanently at night, but they do not occur in the illuminated area.
This extrasolar world, called Kepler-13Ab, is 1,730 light-years away, and is a gas giant of a variety known as hot Jupiter. These stars orbit much closer to their star than Mercury of the Sun; Kepler-13Ab, which is between five and eight times more massive than the largest of the planets in our Solar System, makes a complete revolution around in less than two days.
In his case, in addition, the gravitational pull of the star causes a part to remain always oriented towards it. In this temperatures of 2,760 degrees are reached, which makes it one of the hottest known exoplanets. In the other, on the contrary, darkness always reigns.
According to their discoverers in a statement, it is the first detection of a process of this type in an extrasolar world, and is another example of the complexity of atmospheric processes that can be found in exoplanets.
In addition, they hope that their work can be useful in the study of the habitability of other bodies more similar to Earth.
Thus, Thomas G. Beatty, a professor of astronomy at the aforementioned US institution, who has coordinated this initiative, points out those studies with this type of gaseous worlds can lay the foundations for research focused on other terrestrial planets. “The more we know about their atmospheres and their behavior, the more we will advance in our knowledge of the smaller planets and with more complex gas layers,” he says.
An exotic world
In an essay published in the journal The Astronomical Journal, Beatty and his collaborators indicate that, in principle, his objective was not to specifically look for the aforementioned titanium dioxide, but to find out why the atmosphere of Kepler-13Ab becomes colder at a higher altitude, a phenomenon completely different from what happens in other hot Jupiters. In them, the titanium oxides absorb the luminous radiation and re-irradiate it in the form of heat.
In fact, the atmosphere of the gas giants of the solar system, which are much colder, becomes more temperate at higher altitudes.
Beatty’s group concluded that these oxides had disappeared from the atmosphere of the daytime zone of the planet, probably dragged by intense winds that lead them to the night side. There they condense forming flakes and clouds, and precipitate as if it were snow. However, the intense surface gravity of the planet draws it from the upper layers of the atmosphere and leads it to the lower layers, where it is trapped.
“The climate in other worlds is a complex puzzle, and the fact of being able to observe this process gives us a very important piece,” says astronomer Jason Wright, from the State University of Pennsylvania, who has also participated in this initiative.
“The observations give us clues about the formation of clouds in this type of planets and the role that gravity plays in the composition of its atmosphere,” adds Beatty.
“Probably, this same type of precipitation occurs in most hot Jupiters, but the surface gravity of those studied so far is lower than that of Kepler-13Ab, in which the titanium oxides do not fall as much. Far away, they do it in warmer areas, where they evaporate again and recover their gaseous form “, he concludes.