Date: 3 Jun 2026
Topic: Science
Codebreakers are a fun way to build numeracy skills.
In 2006, astronomers discovered a huge object in space called Eris, in a similar orbit to Pluto, 27% more massive, but with a 2% smaller diameter. Initially, they thought it was actually bigger than Pluto and wondered if they would have to welcome a 10th planet.
Instead, they decided to change the definition of a planet. The new requirements are that it orbits the Sun, is roughly spherical, and has cleared its orbital neighborhood of other objects due to its greater size. Neither Pluto nor Eris passed the third criterion, so they were demoted to dwarf planets.
Both exist near the Kuiper belt in space, which is a very distant, donut-shaped orbit just past Neptune, approximately 30 to 50 AU away from us. Pluto's orbit varies between 30 to 49 AU, but Eris's orbit goes from 38 to 97 AU (making it much more elliptical).
Pluto is occasionally closer to Earth than Neptune, whose orbit is almost perfectly circular around the Sun.
The edge of the solar system is around 2,000 to 100,000 AU from us, with the nearest neighboring star (Proxima Centauri) being only 268,000 AU from us (less than three times the radius of our solar system).