Way back in 2015, NASA's New Horizon's mission flew by the dwarf planet, Pluto. At the time, scientists felt they had this planet figured out. But the images and accompanying data they got from the mission completely blew their minds.
Since 2006 when the International Astronomical Union updated their classification of the word "planet" there's been a huge debate in the public, and in the scientific community, about the fate of dwarf planets. The IAU says a planet has to be a sun-orbiting body that is massive enough to be round, and will have cleared its orbit -- meaning nothing gets in the way as it goes around the sun.
But now, a new paper purports to change everything when it comes to planetary classification. The paper, published in Lunar and Planetary Science, declares a planet as a round body that's never undergone fusion, and has less mass than a star. That's it. This means, Pluto would be planet again-- But it would also bring along Ceres, Eris, Makemake and Haumea... as well as 97 other objects.