CoRoT-2b, located 930 light-years from Earth, has been fascinating astronomers for years. Indeed, winds from east to west seem to sweep the exoplanet. But this means that they travel in a direction that is contrary to similar planets.
“Hot Jupiter” are exoplanets often exceeding the Jupiter mass, but orbiting very close to their star. Thus, like the Moon with the Earth, these objects have one side locked to their star. The substellar point (the point closest to the star) should always be the hottest. At least logically, but it turns out that this point is shifted to the east for most hot Jupiter. This is due in particular to strong parallel winds at the equator. However, CoRoT-2b baffles researchers as its hotspot is in the opposite direction: west of the center. The results of this study were published in the journal Nature Astronomy.
While other hot Jupiter have been detected in recent years, CoRoT-2b continues to intrigue astronomers for two things: its swollen size and the confusing spectrum of light emissions from its surface. “These two factors suggest that something unusual is happening in the atmosphere of this hot Jupiter,” says Lisa Dang, PhD student at McGill University (Canada) and lead author of the study. Using the Spitzer Space Telescope’s infrared camera to observe the planet as it orbits its host star, researchers have been able to map the brightness of the planet’s surface for the first time, revealing the fact that its hotpoint is unusually facing west.
Three possible explanations are considered here, and each of them raises new questions. The planet could be, for example, turning so slowly that a rotation would eventually take longer than a complete orbit of its star. This could create westerly rather than eastward winds – but it would also undermine the theories of the gravitational interaction of the star-planet in such tight orbits. Another explanation is that the atmosphere could be interacting with the planet’s magnetic field to change its wind pattern: this could provide a rare opportunity to study the magnetic field of an exoplanet. Finally, clouds to the east could be distorting the data collected by Spitzer by filtering electromagnetic emissions.
“We will need better data to shed light on the issues raised by our discovery,” says the researcher. “Fortunately, the James Webb Space Telescope, which is scheduled to launch next year, should be able to tackle this problem: armed with a mirror 100 times more powerful than Spitzer, it should provide us with data like never before. “