Planet Nine or No Nine: Infrared Clues and Vera Rubin’s Promise at the Solar System's Edge

In this Ashram video, Alex McColgan examines the Planet Nine mystery, tracing how astronomers search the far outer solar system for a hidden planet. By combining IRAS data from 1983 with the Akari infrared survey from 2006, researchers narrowed from millions of sources to a single candidate whose predicted motion matches a planet nine scenario. The object appears as a warmer pixel in the IRAS data and has shifted by about 47.5 arc minutes over 23 years in Akari images. The Vera Rubin Observatory and its LSST program are poised to confirm or refute Planet Nine with vastly deeper optical data, while alternative explanations including a ZM belt, a past stellar encounter, primordial black holes, or modified gravity remain under consideration.

Overview

In this video, Ashram host Alex McColgan guides viewers through the Planet Nine mystery, a hypothetical large planet far beyond Neptune that could explain irregular orbits among distant icy bodies. The core idea is that the gravity of an unseen planet could sculpt a population of trans Neptunian objects, leading scientists to search for direct imaging of this world.

Why Planet Nine Matters

The presence of a ninth planet would alter our understanding of the solar system’s architecture. The discussion covers how a near circular but inclined prograde orbit could exchange inclination for eccentricity, a scenario described by the Lidov Kozai mechanism, and how this model was used to interpret TNO orbits.

IRAS and Akari: Mining the Archive

A team led by Tomo Goto and Terry Fan cross matched two all sky infrared surveys, IRAS from 1983 and Akari from 2006. The combined dataset contained about 2.4 million objects. Filtering aimed to find a body roughly 7 to 17 Earth masses, with a perihelion near 280 AU and aphelion near 1120 AU. They restricted their search to 500 to 700 AU to avoid regions already surveyed by others.

From Millions to One Candidate

After applying parallax and motion filters, the team reduced the pool to 13 candidates, then narrowed to a single strong contender by eye. The potential Planet Nine signal is faint but, in the infrared, the object would have a specific signature and motion pattern. In the IRAS image, seven pixels appear warmer than the background, while the Akari image taken 23 years later shows the candidate displaced by 47.5 arc minutes, about 1.5 full moons, toward the lower part of the image.

Follow Up: Vera Rubin and LSST

The next key step is follow up with the Vera Rubin Observatory and its 3.2 gigapixel camera. Its Legacy Survey of Space and Time LSST will observe the sky with unprecedented depth, enabling the discovery of many more solar system objects and offering a decisive test for Planet Nine. The project is expected to generate about 20 terabytes of data each night, potentially increasing known objects by up to a factor of 100 over time.

Alternative Explanations

Not everyone is convinced. Some researchers, including Mike Brown and Konstantin Batien, have raised concerns about the inferred orbital inclination of the candidate. If Planet Nine is elusive or absent, several alternative hypotheses could explain the TNO dynamics: a massive Belt similar to a Zadiric Madigan belt, a past close stellar encounter that stirred the outer solar system, a primordial black hole capture, or a modification of gravity such as MOND.

What’s Next

As the Vera Rubin Observatory begins its 10 year LSST survey, scientists expect to either confirm a ninth planet or push the community toward new explanations for the outer solar system’s architecture. The video invites viewers to weigh in with their thoughts on what the Solar System’s edge might hold and highlights the excitement around the search for credible, high quality science.