Sky & Telescope: “Planet X may have left our Solar System Billions of Years Ago”

Using a computer simulation, Huang ran the solar system backward in time for billions of years. He found that the orbits of the three known Sednoids shared some remarkably similar properties just once, in the distant past: Not long after the birth of the solar system, their perihelia clustered at the same solar longitude, and their apsidal lines (the line passing through perihelion, the Sun, and aphelion) were also nearly coincident.

This orbital clustering is a telltale sign that a single event put the Sednoids onto their present paths, an event that happened during the solar system’s youth more than 4 billion years ago. It’s also a sign that nothing has disturbed the slow evolution of those orbits for 4 billion years. In other words, there is no undiscovered planet to be found today.

Huang’s work showed that the culprit could have been a primordial planet, ejected from the solar system only 100 million years after its formation. This rogue planet would now be long gone, orbiting the center of the galaxy rather than our Sun. Other explanations — such as a star from the Sun’s birth cluster passing close by — are also plausible; more work is needed.

Emily Lakdawalla

The Planet X conundrum continues. To me, a massive object causing orbital disruptions in the early solar system remains the most plausible explanation, as I’ve mentioned before – as much as having a black hole practically next door would be an amazing opportunity for observations – and this study is basically reinforcing this view. Absent any visual detections, I’m leaning more and more into the opinion that the initial ‘discovery’ back in 2016 was largely a gimmick to attract more media attention by the guy who ‘killed Pluto’ – an unfortunately too common practice in scientific circles, used to draw funding for their various research areas.

Figure 3. Orbital alignment. Orbits of six KBOs of the Sedna family projected onto the ecliptic plane. […] The major axes of the orbits are seen to align with the direction to the center of the galaxy, with the aphelion oriented toward the Galactic center.

Another recent paper discuses an alternative explanation for these orbital anomalies: modified Newtonian dynamics! Considering the rivalry between MOND and dark matter, this hypothesis is certainly worth further investigation, as it would add additional data to tip the balance in favor of one of these two theories.