Close to 18 years ago, astronomers spotted a miniature, icy world named Eris billions of miles beyond Neptune. But unlike its dwarf planet cousin Pluto — which New Horizons promoted to a rich, dynamic world after its visit in 2015 — Eris has not had any robotic visitors. It is so far away from Earth, in fact, that it shows up in observations just as a single pixel of light.
All in all, scientists know very little about what happens on Eris.
