Object 90377 Sedna—a distant trans-Neptunian object known best for its highly elliptical, 11,390-year long orbit—is currently on its way toward perihelion (its closest approach to the sun) in 2076. After that, Sedna will swing out into deep space again and won't be back for millennia, making this flyby a once-in-a-lifetime (or, once in ~113 lifetimes) opportunity to study an object from the far reaches of our solar system. There are no missions to Sedna in the works just yet, but astronomers are beginning to plan for the possibility, and the ideal launch date for such a mission is approaching fast, with two of the best launch windows coming up in 2029 and 2034.

Sedna was discovered in 2003 by Caltech astronomer Mike Brown and his team, and was one of a series of potential dwarf planets (alongside similar-sized bodies like Haumea, Makemake, and Eris) whose discovery led to the demotion of Pluto in 2006. As best we can tell from a distance, Sedna is about the same size as Ceres, the largest object in the asteroid belt, but its composition and origins are different.