New Dwarf Planet Discovery Challenges Planet Nine Hypothesis

Discovery of a new potential dwarf planet in the outer reaches of the solar system has posed the greatest challenge yet to the hypothesis that a ninth planet lurks far from the sun. This newly found trans-Neptunian object (TNO) named 2017 OF201 has incredibly elongated orbit (1,600 times that of the Earth's orbit) that takes it more than 157 billion miles (244 billion kilometers) from the sun. According to researchers it is very rare to discover an object both large (estimated diameter of 435 miles) and with an exotic orbit.

The New Dwarf Planet

According to the pre-print of a paper describing the discovery, with an estimated diameter of 435 miles, 2017 OF201 is large enough to be considered a dwarf planet. It was detected with the help of the data from both DECaLS and the Canada–France–Hawaii Telescope. The closest point of its orbit to the sun (perihelion) is 44.5 astronomical units (AU)—comparable to Pluto—while its farthest point (aphelion) stretches over 1,600 AU. 2017 OF201 is too far away to be seen with current telescopes; it could only be discovered because its last perihelion came in 1930, and that it's still relatively close.

Scattered Disk, a realm with icy bodies on highly elongated and inclined orbits is situated beyond the Kuiper belt of outer solar system. This discovery hints that many similar objects could exist in the Scattered Disk and beyond. It makes discovery of a trans-Neptunian object (TNO) on a greatly elongated orbit is vital for piecing together the mystery of the outer solar system.

Discarding Planet Nine

The discovery challenges the Planet Nine hypothesis, which suggests a massive, unseen planet is influencing the orbits of distant TNOs. While most extreme TNOs show a clustered pattern that supports this idea, 2017 OF201 does not—its orbit is unusually unclustered.

Although Planet Nine could allow for such deviations, its gravitational pull would render those orbits unstable over millions of years. This mismatch between theory and observation puts Planet Nine's existence under scrutiny.