Hot Jupiters are among the most extreme planets in the universe — fiery gas giants similar to Jupiter or Saturn that orbit so close to their stars that they complete a full revolution in just a few days. A recent study conducted by scientists may potentially redefine the understanding of these celestial bodies.
The Unusual Hot Jupiter CoRoT-2 b
The exoplanet under investigation is CoRoT-2 b, a celestial body possessing a mass approximately 3.5 times that of Jupiter and a diameter 1.5 times greater than that of the largest planet in our solar system, situated roughly 696 light-years from Earth. It completes an orbit around its star in approximately 41 hours. This data is documented on the website www.space.com.
What is particularly noteworthy about CoRoT-2 b? The majority of hot Jupiters are tidally locked, implying that one hemisphere consistently faces their star (the day side), while the opposite hemisphere remains perpetually in darkness, facing outward into space. Nonetheless, a recent investigation of CoRoT-2 b appears to indicate that this hot Jupiter is not tidally locked. This finding constitutes a significant surprise and raises fundamental questions regarding conventional assumptions about these extreme exoplanets.
“I truly find great interest in observing unusual planets — identifying those that deviate from typical characteristics — and in unraveling mysteries,” stated Aurora Kesseli, the team leader at NASA’s Exoplanet Science Institute (NExScI). “Our latest findings demonstrate that the ‘one-size-fits-all’ hypothesis is inadequate, even for longstanding subjects of study. Each new hot Jupiter we examine contributes additional insights that enable us to refine our models, which are invaluable not only for understanding this particular category but also for all types of exoplanets.”
Characteristics of the rotation and climatic conditions of a hot Jupiter
For rocky planets, tidal locking would produce an extraordinarily hot day and a significantly colder night, characterized by an everlasting sunset. Nonetheless, the circumstances for gas giants are comparatively more intricate owing to their dense atmospheres.
This indicates that although hot Jupiters possess day and night sides, they generally exhibit prominent hot spots on the day side, somewhat offset in the direction of their rotation and orbital movement around the star. CoRoT 2b also challenges this expectation, displaying a hot spot in the opposite direction of its orbit. Kesseli and her team examined three potential causes for this anomaly.
The conditions under which tidal locking occurs are of considerable significance to astronomers, as the habitable zone around M dwarfs predominantly resides in the region where this process is anticipated to transpire relatively swiftly. The characteristics of a planet’s rotation markedly influence the distribution of thermal energy across its surface and, as a result, its potential habitability. Consequently, on a planet experiencing tidal locking, the temperature regime, atmospheric circulation, and climate are expected to differ substantially from those on a planet with free rotation.
By determining the orbital velocity of CoRoT-2 b, Kesseli and her colleagues elucidated that a single rotation of this hot Jupiter spans approximately three Earth days. This duration is nearly double its orbital period of around 1.5 Earth days. Consequently, within a single rotational cycle, the planet completes nearly two orbits around its star.
The team’s research was presented at the 248th meeting of the American Astronomical Society in Pasadena, California, and published on the arXiv preprint server.
