The hunt for planets beyond our solar system has turned up more than 4,000 far-flung worlds, orbiting stars thousands of light years from Earth. These extrasolar planets are a veritable menagerie, from rocky super-Earths and miniature Neptunes, to colossal gas giants. Among the more confounding planets discovered to date are “hot Jupiters” – massive balls of gas that are about the size of our own Jovian planet but that zing around their stars in less than 10 days, in contrast to Jupiter’s 12-year orbit, writes Jennifer Chu of the Massachusetts Institute of Technology. Scientists have discovered about 400 hot Jupiters to date. How these weighty whirlers came to be remains one of the big unsolved mysteries in planetary science. Now, astronomers have discovered one of the most extreme ultra-hot Jupiters – a gas giant that is about five times Jupiter’s mass and blitzes around its star in just 16 hours. The planet’s orbit is the shortest of any known gas giant. Due to its extremely tight orbit and proximity to its star, the planet’s day side is estimated to be at around 3,500 Kelvin, or close to 6,000 degrees Fahrenheit – about as hot as a small star. This makes the planet, designated TOI-2109b, the second hottest detected. Judging from its properties, astronomers believe that TOI-2109b is in the process of “orbital decay,” or spiraling into its star, like bathwater circling the drain. Its short orbit is believed to cause the planet to spiral toward its star faster than other hot Jupiters. The discovery, which was made by NASA’s Transiting Exoplanet Survey Satellite (TESS), an MIT-led mission, presents a unique opportunity for astronomers to study how planets behave as they are drawn in and swallowed by their star. “In one or two years, if we are lucky, we may be able to detect how the planet moves closer to its star,” says Ian Wong, lead author of the discovery, who was a postdoc at MIT during the study and has since moved to NASA Goddard Space Flight Center. “In our lifetime, we will not see the planet fall into its star. But give it another 10 million years, and this planet might not be there.” The discovery is reported today in the Astronomical Journal and is the result of the work of a large collaboration that included members of MIT’s TESS science team and researchers from around the world. On May 13, 2020, TESS began observing TOI-2109, a star located in the southern portion of the Hercules constellation, about 855 light years from Earth. The star was identified by the mission as the 2,109th “TESS Object of Interest,” for the possibility that it might host an orbiting planet. Over nearly a month, the spacecraft collected measurements of the star’s light, which the TESS science team then analysed for transits – periodic dips in starlight that might indicate a planet passing in front of and briefly blocking a small fraction of the star’s light.