Discovered in 2015, 850 light-years from Earth in the constellation La Naupe, exoplanet WASP-121b is a doomed world. Too close to its star, it goes around it in just 30 hours, and will eventually be dislodged by tidal forces… in a few tens of millions of years. Signs of this announced destruction are already visible as the star is no longer round but has taken on the shape of a rugby ball. Observed several times by the Hubble telescope, it offers astronomers the opportunity to study its complex weather system, which hides amazing features.
Locked “Hot Jupiter”
WASP-121b is a “super-hot Jupiter” type planet: its mass is about 1.2 times that of the solar system giant, but it is much larger, about twice that of the latter. Its proximity to its star, which is hotter and brighter than the sun, means the planet is “locked in” by the play of gravity: the two objects are in synchronous rotation. Like the Moon around the Earth, WASP-121b always represents the same hemisphere facing the star. One can reach temperatures as high as 3,000°C, while the other, much cooler one, remains submerged in the night and exposed to the cold of space. A situation faced by all exoplanets found in this configuration. The large temperature difference between the two hemispheres causes strong winds, the speed of which can reach 18,000 km/h. They convey a heap of elements evaporated by the heat reigning on the illuminated face. Previous studies have already revealed the presence of heavy metals such as iron, chromium, magnesium and aluminum, as well as water molecules, in the atmosphere.
New Hubble studies by Thomas Mikal-Evans of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, have revealed more about the atmospheric circulation around this exoplanet. To do this, the Mikala-Evans team tracked two complete orbits of WASP-121b (in 2018 and 2019) using the space telescope’s spectroscopic camera. The instrument observes light and breaks it down into its component wavelengths, the intensity of which gives astronomers clues about the temperature and composition of the atmosphere. The latter focused in particular on the spectral line of water and studied its changes during two orbits.
Discovered in 2015, 850 light-years from Earth in the constellation La Naupe, exoplanet WASP-121b is a doomed world. Too close to its star, it goes around it in just 30 hours, and will eventually be dislodged by tidal forces… in a few tens of millions of years. Signs of this announced destruction are already visible as the star is no longer round but has taken on the shape of a rugby ball. Observed several times by the Hubble telescope, it offers astronomers the opportunity to study its complex weather system, which hides amazing features.
Locked “Hot Jupiter”
WASP-121b is a “super-hot Jupiter” type planet: its mass is about 1.2 times that of the solar system giant, but it is much larger, about twice that of the latter. Its proximity to its star, which is hotter and brighter than the sun, means the planet is “locked in” by the play of gravity: the two objects are in synchronous rotation. Like the Moon around the Earth, WASP-121b always represents the same hemisphere facing the star. One can reach temperatures as high as 3,000°C, while the other, much cooler one, remains submerged in the night and exposed to the cold of space. A situation faced by all exoplanets found in this configuration. The large temperature difference between the two hemispheres causes strong winds, the speed of which can reach 18,000 km/h. They convey a heap of elements evaporated by the heat reigning on the illuminated face. Previous studies have already revealed the presence of heavy metals such as iron, chromium, magnesium and aluminum, as well as water molecules, in the atmosphere.
New Hubble studies by Thomas Mikal-Evans of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, have revealed more about the atmospheric circulation around this exoplanet. To do this, the Mikala-Evans team tracked two complete orbits of WASP-121b (in 2018 and 2019) using the space telescope’s spectroscopic camera. The instrument observes light and breaks it down into its component wavelengths, the intensity of which gives astronomers clues about the temperature and composition of the atmosphere. The latter focused in particular on the spectral line of water and studied its changes during two orbits. This data enabled the mapping of the temperature profile on both sides, first detailed in an article published in the journal Astronomy of nature.
Another artist’s idea of a planet distorted by tidal forces. Image Credit & Copyright: NASA, ESA and J. Olmsted (STScI).
Rain of gems
Thus, it has been established that in the irradiated hemisphere the temperature fluctuates by more than 1000 °C (1500 K) from 2500 K in the lowest layer of the atmosphere to 3500 K at the highest measurable altitude. The variations have a much smaller amplitude on the reverse side: from 1800 K in the deep layer to 1500 K in the upper atmosphere. Interestingly, the temperature profiles change, increasing with height on the day side and falling with height on the night side. Another noteworthy element: the hottest point of the illuminated face is not at the “zenith”, vertical to the rays of its Sun. It is shifted to the east, which indicates the presence of strong winds (blowing from west to east) that move heated atmospheric gas before it has time to radiate thermal radiation back into space. These winds carry hydrogen and oxygen molecules to the far side, where cooler temperatures allow them to recombine into water vapor, which is re-delivered to the day side of Wasp-121b, thus maintaining a water cycle very different from what we can imagine. know on earth.
However, on the dark side of Wasp-121b, the temperature is not cold enough for water to condense and fall as rain there. But they are cold enough for other metallic elements present in the atmosphere to do so. Thus, clouds made of titanium, iron and aluminum can generate metallic rain in the deepest atmosphere on the dark side. However, the authors of the study note, aluminum could condense as corundum (aluminum oxide), which, if it contains traces of elements such as iron, titanium or chromium, forms rubies and sapphires. So it might rain gems on the Wasp-121b! This unique glimpse of a “hot Jupiter” may soon be cleared up by observations made with the James Webb Telescope, a slot already reserved for this purpose. Therefore, a new weather report from Wasp-121b is expected soon!