Speaker
Description
The outer solar system is theoretically predicted to harbor an undiscovered planet, often referred to as Planet Nine (P9). Simulations suggest that its gravitational influence could explain the unusual clustering of distant Kuiper Belt Objects. However, no observational evidence for P9 has been found so far, as its predicted orbit lies far beyond Neptune, where it reflects only a faint amount of sunlight. A feasible solution is to detect thermal emission from P9 in the far-infrared, rather than using optical surveys. Extended from our recent study (Phan T. L. et al., 2025, PASA, 42, e064), this work aims to find P9 in the far-infrared all-sky survey data from IRAS catalogs and AKARI Monthly Unconfirmed Source List (MUSL). After applying the positional and flux criteria, we produced all possible pairs of IRAS and AKARI sources whose 23-year angular separations were limited between 42' and 166', corresponding to the orbital motion of P9 at 280 - 700 AU. For each pair, we continued to search for the third detection in AKARI data based on the expected parallax motion of P9 over 6 months. We present the preliminary results after manually checking their IRAS/AKARI cutout images. Multiple-detection P9 candidates are important in estimating orbital parameters and comparing them to the simulation results.