This weird 'hot Jupiter' exoplanet has a hotspot in the wrong place, and astronomers aren't sure how

Hot Jupiters are some of the most extreme planets in the universe, blazing gas giants like Jupiter or Saturn that exist so close to their stars that they complete orbits in a matter of days. Now, new research may rewrite the definition of these planets that make the solar system look a little bit mundane. The extrasolar planet, or exoplanet , at the heart of this rethink is CoRoT-2 b, a world with 3.5 times the mass of Jupiter and 1.5 times the size of our solar system's largest planet, located around 696 light-years away. It orbits its star in just 41 hours or so. What is so strange about CoRoT-2 b? Most hot Jupiters are tidally locked, meaning they have one side that permanently faces their stars, a "dayside," and a "nightside" that faces out into space in perpetuity. However, a new investigation of CoRoT-2 b seems to show that this hot Jupiter isn't tidally locked, and that is a big surprise, one that challenges all our assumptions about these extreme exoplanets . "I really like looking at the weird ones — finding planets that don't fit the standard picture — and doing some mystery solving," team leader Aurora Kesseli of the NASA Exoplanet Science Institute (NExScI) said in a statement. "Now we can see that a one-size-fits-all model does not work, even for planets that we've been studying for a long time. Every time we look at another hot Jupiter, we learn something new to help refine our models, which are useful for understanding not only hot Jupiters, but for all types of exoplanets." The cosmic dance of hot Jupiters For rocky planets, tidal locking would result in an incredibly hot dayside and a much cooler nightside, divided by a perpetual sunset. However, the situation for gas giants is somewhat more complicated because of their swirling atmospheres. This means while hot Jupiters have day and night sides, they usually possess large hot spots on the dayside, shifted slightly towards the direction of their rotation and their orbit around the host star. CoRoT 2b defies this expectation too, possessing a hotspot in the opposite direction of its orbit. Kesseli and the team investigated three possible reasons for this abnormality. "The conditions for tidal locking are important for astronomers to understand because the habitable zone for planets around M dwarfs is within the tidal locking zone, where we expect tidal locking to happen pretty quickly," Kesseli said. "The way that a planet rotates greatly affects how the planet distributes its heat, and therefore affects its habitability, so for a planet that is tidally locked, the temperatures, winds, and climates are going to look completely different than those of a planet that is not tidally locked." An illustration shows the non-tidally locked planet CoRot 2 b rotating in the opposite direction compared to a tidally locked hot Jupiter (Image credit: Keith Miller (Caltech/IPAC - SELab).) Measuring the velocity of CoRoT-2 b, Kesseli and colleagues found that one day on this hot Jupiter is about three Earth days, which is almost twice as long as its year which lasts around 1.5 Earth days. This means that its day is much shorter than its year; by the time CoRoT-2 b completes one rotation, it has made almost two orbits of its parent star. "I was very pleasantly surprised when I tried a bunch of methods, and I was like, 'Aha! This is actually like one of the three hypotheses!' Seeing the data pretty clearly pointing towards one of them was just really exciting," Kesseli said. The next step for Kesseli is to discover what is causing the slow rotation of CoRoT-2 b. "Hot Jupiters are the first type of planet where we have been able to really explore and refine our models of their climates," said Kesseli. "With the next generation of telescopes like the Habitable Worlds Observatory and the Extremely Large Telescope , we’ll be able to do more in-depth measurements across more planets, maybe even potentially habitable ones." The team's research was presented at the 248th meeting of the American Astronomical Society in Pasadena, California, and has been published on the paper repository site arXiv .