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Astronomers have found a hot, rocky “super Earth” that has existed since almost the dawn of our Milky Way galaxy. It could profoundly alter the search for intelligent life. Around 280 light-years distant, TOI-561b is a rocky world a third bigger than Earth that orbits its star in just 10.5 hours. It’s thought to be around 10 billion years old—twice as old as the Solar System—when the majority of stars in our galaxy were first beginning to shine. The Milky Way is about 12 billion years old. The confirmation of TOI-561b demonstrates that rocky planets may have been forming for most of the history of the Universe. “TOI-561b is one of the oldest rocky planets yet discovered,” said Lauren Weiss, team leader and postdoctoral fellow at the University of Hawaii. “Its existence shows that the Universe has been forming rocky planets almost since its inception 14 billion years ago.” The team’s paper was presented at the recent 237th meeting of the American Astronomical Society and will appear in The Astronomical Journal in February 2021. The discovery of TOI-561b has consequences for alien-hunting. “It means that rocky planets have potentially been forming for the past 10 billion years—and perhaps all 12 billion years of our galaxy’s history,” said Weiss. “Imagine what could have happened on a rocky planet that's been around for 10 billion years—I’d sure like to find out.” Astronomers have found three planets—TOI-561b, TOI-561c and TOI-561d—using NASA's planet-hunting Transiting Exoplanet Survey Satellite (TESS ) space telescope and Keck Observatory in Hawaiʻi. They’re orbiting a star called (you guessed it) TOI-561, which is a star in the “galactic thick disk”—and that’s what makes this discovery so important. Here’s what else we know about TOI-561b and its star: Most spiral galaxies like our own Milky Way have two disks-- 1) a “galactic thin disk” containing dust, gas, stars and planets along the plane, and 2) a “galactic thick disk” that hosts metal-poor stars. It’s thought that their lack of metal—principally iron and magnesium—means that stars in the thick disk lack planets. Most planets found by astronomers orbit stars in the thin disk. However, that’s not the case with the TOI-561 star system, which was found in the thick disk where planets are not thought to form around stars. That makes TOI-561b one of the first confirmed rocky exoplanets found in the thick disk of the Milky Way— and suggests that rocky planets have been evolving since the beginning of the Universe around 14 billion years ago. That suggests that ancient lifeforms may have existed for many billions of years. Stars in the galactic thick disk may have formed in an ancient galaxy that later merged with our own, or they could be the first stars that formed within the Milky Way. “I wonder what view of the night sky would have been accessible from the rocky planet during its history,” said Weiss. TOI-561b hints that rocky planets may have been forming for most of the history of the Universe. 
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