Outside our solar system, there are enormous, extremely hot, alien-worlds. These mysterious exoplanets were originally thought to be the misfits of the cosmos, but it turns out, there are hundreds of them and they’re the source of a lot of speculation. Astronomers call these exoplanets, hot-Jupiters because they have a similar mass and composition as our solar system’s largest planet. They are, however, for the most part, much larger and have a greater volume and as the name suggests they are hot, like really really hot. The first hot Jupiter was discovered in 1995. Astronomers spotted the exoplanet orbiting extremely close to its parent star - so close that it caused the star to wobble. This observation inspired a new process of exoplanetary discovery called the radial-velocity method aka the ‘wobble method’. It works like this: scientists use the light spectrum to measure the movement of a star. If the star’s light waves compress together and then stretch out, it’s color signature will change indicating that the star is in fact, wobbling. And this is a sign that a hot-Jupiter may be close by. Astronomers still use the wobble method today and it’s contributed to the discovery of hundreds of hot Jupiters. These exotic extrasolar gas giants have a few characteristics in common. Like we mentioned earlier, hot Jupiters are located feverishly close to their parent stars. Take, OGLE-TR-56b for example. Astronomers discovered this hot Jupiter clinging to its parent star at a distance of about 0.02 AU. AU stands for astronomical unit and 1 AU represents the average distance from Earth to the Sun. To put that into perspective, Mercury orbits the sun at 0.39 AU. So OGLE-TR-56b is about fourteen times closer to its parent star than Mercury is to the Sun. Because of this close proximity, hot Jupiters have scorching surface temperatures. Since they are tidally locked, only one side of these exoplanets faces its parent star. While, both sides reach extreme temperatures, the dayside is much hotter. KELT-9b is the hottest gas giant on record with a dayside temperature of more than 7,800 degrees Fahrenheit. That’s about nine times hotter than the average temperature on Venus - the hottest planet in our solar system. The temperatures of hot Jupiters fluctuate as they orbit their parent star at a rapid pace. Their orbital periods are typically shorter than 10 Earth days. WASP-18b has one of the shortest orbits ever discovered. It takes this massive exoplanet just 23 hours to rotate around its star in an almost perfectly circular orbit. But the orbital paths of younger hot Jupiters are thought to be more unconventional, because they’re further away from their parent stars. HD 80606b for example, has a particularly unusual route. During its elliptical orbit the hot Jupiter swings close to its star at speed and then shoots back out at a great distance. Scientists believe this exoplanet is in the process of migrating towards its star, and it’s path could help explain how hot Jupiters are formed. One of the leading hot Jupiter formation theories holds that these gas giants were born farther away from their stars, but over hundreds of millions of years, are driven inward by the gravitational influences. And as a hot Jupiter migrates closer to its star, its orbital path becomes more circular. But when a hot Jupiter’s orbit becomes too close, it will enter a death spiral. The tidal forces from its much larger parent star, will ultimately destroy the gas giant. Yes, it is a bittersweet ending for these beautiful bizarre worlds, and as more hot Jupiters approach their demise, we will form a better understanding of the mysterious objects inhabiting the cosmos.
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