I have often said that planets come in a wide range of sizes, but rarely do I find myself stating that they also come in a wide range of shapes! The discovery of WASP-107b is a good example, as this planet is the size of Jupiter but only a tenth of its mass. But there's more… Using the James Webb Space Telescope, a team of astronomers has precisely identified that the planet has an east-west asymmetry in its atmosphere, that is, it is unbalanced. It is tidally locked to the star and on one side the atmosphere appears to be inflated compared to the other.
Planets that orbit other stars are known as exoplanets. WASP-107b is one such planet orbiting a star 200 light years away in the constellation Virgo. The first detection of exoplanets was confirmed in 1992 and since then more than 5,000 extraterrestrial planets have been identified. A multitude of different techniques are used to hunt them, from looking for light falls in distant stars to analyzing a star's spectrum. A wide variety of planetary systems have been found, from possibly habitable Earth-like planets to large gas giants like Jupiter. With the new generation of space telescopes like the JWST it is now possible to study the atmosphere of exoplanets to learn even more about them.
A team of astronomers from the University of Arizona has been using JWST with an international group of researchers to study WASP-107b. They discovered the planet's east-west asymmetry as it passes in front of its host star, just as the Moon does during a solar eclipse.
The shape of the planet is an atmospheric phenomenon, but of course when it comes to gas giants like Jupiter, that more or less refers to the planet itself. However, it is not just a physical asymmetry, since there are differences in temperature and cloud properties between the eastern and western hemisphere. It is now important to explore the observed asymmetry to learn more about the planet's dynamics and whether it is a unique phenomenon.
One element of the planet that is the subject of investigation and probable cause is that it is tidally locked to the star. The gravitational force of the star and the gravitational force of the planet have acted on each other to fix one face of the planet to the star. This means that one hemisphere is constantly illuminated and heated by the star while the other hemisphere is permanently at night! However, tidal locking is not unique to WASP-107b, so if this is the cause, then asymmetry should be common.
To reach their discovery, the team used a technique known as transmission spectroscopy. In this technique, observations are made of starlight as it passes through the planet's atmosphere during transit events. As light passes through atmospheric gases, the presence of different gases interacts with the light in different ways that can be observed during spectral analyses.
What makes WASP-107b unique is the low gravity and low density, resulting in a somewhat overinflated atmosphere compared to other alien worlds of this mass. This is the first time such an asymmetry has been observed, so it will be interesting to see how unique this fascinating world really is.
Fountain : Astronomers glimpse a uniquely inflated and asymmetric exoplanet
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