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Astronomers May Have Discovered Fastest-Moving Exoplanet System Ever Seen “We think this is a so-called super-Neptune world orbiting a low-mass star at a distance that would lie between the orbits of Venus and Earth if it were in our Solar System,” said Dr. Sean Terry, a postdoctoral researcher at the University of Maryland, College Park and NASA’s Goddard Space Flight Center. “Since the star is so feeble, that’s well outside its habitable zone. If so, it will be the first planet ever found orbiting a hypervelocity star.” The system was first spotted indirectly in 2011 thanks to the microlensing event MOA-2011-BLG-262. If the pair was a rogue exoplanet and an exomoon, they’d be effectively invisible — dark objects lost in the inky void of space. “Microlensing occurs because the presence of mass warps the fabric of space-time,” the astronomers explained. “Any time an intervening object appears to drift near a background star, light from the star curves as it travels through the warped space-time around the nearer object.” “If the alignment is especially close, the warping around the object can act like a natural lens, amplifying the background star’s light.” In MOA-2011-BLG-262, microlensing signals revealed a pair of celestial bodies. The astronomers determined their relative masses (one is about 2,300 times heavier than the other), but their exact masses depend on how far away they are from Earth. “Determining the mass ratio is easy. It’s much more difficult to calculate their actual masses,” said Dr. David Bennett, a senior research scientist at the University of Maryland, College Park and NASA’s Goddard Space Flight Center. The MOA-2011-BLG-262 discovery team suspected the microlensed objects were either a star about 20% as massive as our Sun and a planet roughly 29 times heavier than Earth, or a nearer rogue planet about four times Jupiter’s mass with an exomoon. To figure out which explanation is more likely, Dr. Terry, Dr. Bennett and their colleagues searched through data from the Keck Observatory in Hawaii and ESA’s Gaia satellite. The researchers found a strong suspect located about 24,000 light-years away, putting it within the Milky Way’s Galactic bulge. By comparing the star’s location in 2011 and 2021, they calculated its high speed. But that’s just its 2D motion; if it’s also moving toward or away from us, it must be moving even faster. Its true speed may even be high enough to exceed the Galaxy’s escape velocity of 600 km per second (1.3 million mph). If so, the planetary system is destined to traverse intergalactic space many millions of years in the future. “To be certain the newly identified star is part of the system that caused the 2011 signal, we’d like to look again in another year and see if it moves the right amount and in the right direction to confirm it came from the point where we detected the signal,” Dr. Bennett said. “If high-resolution observations show that the star just stays in the same position, then we can tell for sure that it is not part of the system that caused the signal,” said Dr. Aparna Bhattacharya, also from the University of Maryland, College Park and NASA’s Goddard Space Flight Center.