Who discovered Eris the dwarf planet?

The Story of Eris: How a Rogue World Rocked the Solar System

Out beyond Neptune, in the really, really far reaches of our solar system, a team of astronomers was on a mission: to find what other secrets might be lurking out there. Little did they know, their search would lead to a discovery that would turn our understanding of the cosmos on its head.

Meet the Discovery Team

The credit for spotting Eris goes to Mike Brown, Chad Trujillo, and David Rabinowitz. Brown was the guy at Caltech, Trujillo was hanging out at the Gemini Observatory, and Rabinowitz was over at Yale. Since 2001, they’d been using the Samuel Oschin telescope at Palomar Observatory in Southern California, carefully scanning the outer solar system, hoping to find something new. It was like searching for a needle in a cosmic haystack!

The Day Eris Appeared

Funnily enough, they actually snapped the first pictures of Eris way back on October 21, 2003. But here’s the thing about space: things move slow. Eris was so far away that it barely seemed to budge, so the team didn’t realize what they had right away. It wasn’t until January 5, 2005, that someone had the bright idea to re-analyze the old data. Bingo! There it was, this distant world, just waiting to be found. The official announcement came on July 29, 2005, and the astronomy world went wild.

From “Xena” to Eris: A Naming Saga

Before it had a proper name, the team playfully nicknamed the object “Xena,” after the warrior princess. And its moon? That became “Gabrielle.” Cute, right? Of course, these were just temporary nicknames. The real naming had to go through the International Astronomical Union (IAU), the official body for all things space-naming related. On September 6, 2006, the team formally suggested the name Eris, after the Greek goddess of discord. Why Eris? Well, according to Brown, Eris was chosen because she “caused strife and discord by causing quarrels among people, and that’s what this one has done too.” Sounds about right! The IAU gave the thumbs up on September 13, 2006. And Eris’s moon? It got the equally cool name Dysnomia, after the demon goddess of lawlessness, who also happened to be Eris’s daughter. Talk about a family affair!

The Planet That Wasn’t (Quite)

Here’s where things get interesting. Eris is a big deal – the ninth-most massive object orbiting the Sun and the second-largest dwarf planet we know of. When it was first discovered, some astronomers thought it might even be bigger than Pluto! This sparked a huge debate: what exactly is a planet, anyway? The IAU stepped in and, in 2006, laid down the law. To be a “planet,” an object had to orbit the Sun, be round-ish thanks to its own gravity, and have “cleared the neighborhood” around its orbit. That last part is key. Pluto and Eris both hang out in the Kuiper Belt, a crowded space filled with other icy objects. Since they hadn’t “cleared” their orbital path, they didn’t make the cut. So, Pluto got reclassified as a dwarf planet, joining Eris and Ceres in this new category. It was a demotion that rocked the world (or at least, the astronomy world).

Eris Today: Still Out There, Still Mysterious

Today, Eris is still way out there in the scattered disc, even further than the Kuiper Belt. It takes a whopping 557 Earth years for Eris to make just one trip around the Sun! It’s about 2,326 kilometers (1,445 miles) across, made mostly of rock and ice, and probably has a surface covered in frozen methane and nitrogen. Because it’s so far away and small, Eris is a tough target for telescopes. But astronomers haven’t given up. By studying Eris, they hope to unlock more secrets about the early days of our solar system and the wild, wonderful diversity of objects that call it home.