Overview

• Ammonite is the fourth known sednoid, tracked over 19 years through combined Subaru, CFHT and archival observations.
• Numerical simulations show its orbit has remained stable for 4.5 billion years, diverging from other sednoids around 4.2 billion years ago.
• Its perihelion of roughly 66–71 astronomical units fills the ‘q-gap’ in the distribution of distant Solar System bodies.
• No known transfer mechanism within the current planetary configuration can explain its distant orbit, implying external gravitational influences shaped its trajectory.
• The upcoming Vera C. Rubin Observatory LSST survey is being prepared to expand the census of outer Solar System objects and further test remaining Planet Nine scenarios.