The discovery was published this week in the scientific journal nature. According to Leanne Dessen of the University of Leuven, one of the three lead authors of the article, more exotic exoplanets (planets orbiting other stars) have been discovered in recent years, “but this is a very extreme case.”
Other researchers are reacting enthusiastically to this surprising discovery. “These results show how incredibly diverse and complex exoplanet atmospheres are,” said Sarah Seager of MIT, one of the world’s leading exoplanet researchers.
Her colleague Yamila Miguel from the Leiden Observatory thinks the same way. “This kind of information helps us better understand how planets work, form and evolve,” she says. The fact that we can study and characterize these distant worlds in such detail is, according to Miguel, “the real wow factor of this article.”
Low density
The planet it orbits is called WASP-107b. It was discovered in 2017 by the South African Wide-Angle Planet Search Station (WASP). It rotates once every 5.7 days in a small circular orbit around a star smaller and one degree cooler than the sun, and about 200 light-years away from us, in the constellation Virgo. Previous measurements have already shown that WASP-107b is roughly the same size as the giant planet Jupiter in our solar system. However, its mass is at least ten percent of Jupiter’s mass. This means that the average density is still much lower than that of balsa wood – hence the nickname “Cotton Candy Planet”.
As seen from Earth, WASP-107b passes in front of its parent star on each orbit (as detected), and during this “transition” a small portion of the star’s light is slightly “filtered” by the thin, expansive atmosphere. of the Earth. planet. This makes it possible to study the composition of this atmosphere. For example, in 2018 the Hubble Space Telescope detected helium (the second lightest element) in the atmosphere of the planet WASP-107b. The presence of water vapor has also been previously proven.
However, the James Webb Space Telescope (JWST), launched at the end of 2021, is much more sensitive than Hubble with its 6.5-meter-diameter mirror. Moreover, he makes his observations at infrared wavelengths, specifically that part of the electromagnetic spectrum in which many molecules leave their spectral “fingerprints.” “The plan to observe WASP-107b with the James Webb Space Telescope goes back long before launch,” Dessen says. The observations were made using the mid-infrared instrument (MIRI) at the beginning of this year.
Surprises
It quickly became clear that WASP-107b held many surprises for the research team. It turns out that the atmosphere contains a much greater amount of sulfur dioxide (SO2) than expected. But according to Dessen, this prediction was based on calculations from existing models. “It turns out they didn’t take sufficient account of the fact that the atmosphere is very thin,” she says. “Starlight thus penetrates more easily to great depths, causing other chemical reactions to occur.”
Methane gas (CH4) On the other side no It has been discovered that, while you might expect it, there is also a lot of methane in the atmospheres of the giant planets in our solar system. From this, Dessen and her colleagues conclude that the temperature in the atmosphere of WASP-107b is increasing very quickly and deeply. While the planet is about 500 degrees hot from the outside (thanks to its small distance from its parent star – only 8.5 million kilometers), the temperature at a depth of about a thousand kilometers must already be at least 1000 degrees, otherwise there would have been much more formation. From methane gas.
This high temperature probably explains how the largely gaseous planet became “inflated.” but Why Whether the planet is warming is a mystery, according to Michael Main of the Dutch space research institute SRON, another of the lead authors of the research. naturecondition. “It can’t be residual heat from creation,” he says. “The planet is already too old for that.” Tidal effects may play a role, but no one knows for sure. There is still a lot of speculation going on.
Sand clouds
The high temperature in the deep layers of WASP-107b’s atmosphere fits well with the exciting discovery of “sand clouds” in the thin upper layers. MIRI observations indicate the presence of microscopic grains of silicon oxide (SiO) or silicon dioxide (quartz, SiO2) – the main component of sand. Maine believes that with the high wind speeds that occur here, a spaceship descending into the planet’s atmosphere would almost certainly be hit by heavy sand.
Such small solid grains flap quickly back into the thin atmosphere, so it seems there must be an atmospheric circulation somewhat reminiscent of the water cycle on Earth. At a depth of about a thousand kilometers, the falling grains evaporate due to the high temperature. The resulting gas molecules are then lifted into the atmosphere by vertical movements, where they condense back into solid particles.
“This seems very plausible,” says Sarah Seager, who predicted these types of clouds in 2000. The fact that it could actually be observed seemed like a distant possibility more than twenty years ago. However, thanks to the James Webb Space Telescope, research has accelerated. “Nowadays, exoplanetary atmospheres are being discovered so rapidly that it is almost impossible to keep up,” Seager says.
Puzzles
There are still many unanswered questions. How planets like WASP-107b become so strongly “inflated,” according to Yamila Miguel, is still “unknown and subject to debate.” Also, no one knows whether these types of “hot Jupiters” have a solid core, and what they are made of. “Almost nothing is known about the cores of the giant planets in our solar system, let alone distant exoplanets,” says Miguel.
What is certain is that WASP-107b is slowly but surely “evaporating” under the influence of ultraviolet radiation from its parent star. Who knows, maybe the atmosphereless “super-Earth” will eventually be left behind, as Michel Min speculates. Seager does not dare to make any statements on this subject. “I’m inclined to believe that this mysterious planet will continue to defy all our interpretations for a long time to come.”
