The Solar System consists of our star, the Sun, and everything bound to it by gravity; the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, along with dwarf planets like Pluto, dozens of moons, and millions of asteroids and comets.
The planets orbit the Sun in elliptical paths, with the inner four being rocky terrestrial worlds and the outer four being gas and ice giants many times larger than Earth.
Our fascination with hunting down more planets in the Solar System has until now not revealed any strong candidates.
With Pluto having been classed as the 9th planet for many years, the hunt was on for Planet X.
With the demotion of Pluto in 2006, the idea of Planet Nine was first proposed in 2016 by astronomers Batygin and Brown.
Its existence is inferred from unusual orbital clustering of several trans-Neptunian objects, suggesting they’re being influenced by a large, unseen planetary body.
Despite extensive searches using powerful telescopes, Planet Nine has remained theoretical as direct observation has proven elusive.
In a study led by Terry Long Phan and published in Cambridge University Press, the team searches for Planet Nine candidates by using two far-infrared all-sky surveys, IRAS and AKARI, whose 23-year separation allows detection of Planet Nine’s expected orbital motion (~3′/year).
The search uses the AKARI Far-Infrared Monthly Unconfirmed Source List (AKARI-MUSL), which is better suited for identifying faint, moving objects than the standard AKARI Bright Source Catalogue.
Researchers estimated Planet Nine’s expected flux and motion based on assumed mass, distance, and temperature, then applied positional and flux criteria to match sources between IRAS and AKARI.
They identified 13 candidate pairs with angular separations corresponding to heliocentric distances of 500–700 AU and masses of 7–17 Earth masses.
After a rigorous analysis and selection process, including visual inspection of images, the team identified one strong candidate pair, where the IRAS and AKARI sources showed the expected angular separation (42′–69.6′) and were not detected at the same position in each survey.
The AKARI detection probability map confirmed the candidate’s consistency with a slow-moving object, showing two detections on one date and none six months earlier.
However, IRAS and AKARI data alone are insufficient to determine a precise orbit so there will need to be follow-up observations with DECam, which can detect faint moving objects within about an hour of exposure, are suggested to confirm the candidate and fully determine its orbit, aiding in understanding the solar system’s evolution and structure.
The search for Planet Nine continues to push the boundaries of astronomical discovery using advanced survey techniques and paring it with careful analysis.
While the identification of a promising candidate is an exciting step forward, confirmation will require further observations and continued collaboration across the astronomical community.
If Planet Nine is ultimately detected, it would mark a monumental addition to our understanding of the Solar System.
Written by Mark Thompson/Universe Today.
