After studying thousands of computer simulations of the solar system, researchers at Rice University and the Planetary Science Institute think there’s a 40% chance an elusive “Planet Nine” or “Planet X” might exist in the outer solar system. It’s the latest hint that there may be an undiscovered world beyond the orbit of Neptune and dwarf planet Pluto.
Atmosphere and clouds. Exploration of far galaxies. Elements of this image furnished by NASA. (url: ... More
The new study published in Nature Astronomy reveals that “wide-orbit” planets — those that orbit the sun from at least 100 times farther than Earth orbits the sun — may be a natural consequence of how planets form.
According to NASA, planets form from the giant, donut-shaped region of gas and dust that surrounds young stars, known as a protoplanetary disk. As planets jostle for space, the chaos can cause some to be flung into much wider orbits.
The research increases the likelihood that Planet X or Planet Nine, hypothetical planets that may or may not exist in the outer solar system, actually exist.
“Essentially, we’re watching pinballs in a cosmic arcade,” said André Izidoro, lead author of the study and assistant professor of Earth, environmental and planetary sciences at Rice University. “When giant planets scatter each other through gravitational interactions, some are flung far away from their star.”
If the timing and surrounding environment are just right, those planets don’t get ejected but are trapped in extremely wide orbits — which could have happened in the solar system as Uranus and Neptune grew or the later scattering among gas giants. “There is up to a 40% chance that a Planet Nine-like object could have been trapped during that time,” said Izidoro. “We’re not just increasing the odds of finding Planet Nine — we’re opening a new window into the architecture and evolution of planetary systems throughout the galaxy.”
Various objects have been discovered beyond Neptune in highly elongated yet remarkably similarly oriented orbits, as if the gravitational influence of a planet midway between Earth and Neptune, in mass, has herded them. If it exists, it’s in the Kuiper Belt, a region of the solar system beyond Neptune that's home to Pluto, other dwarf planets and comets. In May, scientists in Taiwan, searching for a ninth planet, found hints of something in archival images taken by long-dead infrared telescopes. It's hoped that the Vera C. Rubin Observatory — which will use the world's most powerful camera to survey the sky starting later in 2025 — will either find or rule out Planet Nine.
In 2006, the International Astronomical Union reclassified Pluto's status from a planet to a “plutoid,” which was later changed to a dwarf planet. It's become fashionable to deny this, maintaining that the solar system must still have nine planets. However, Pluto’s status was changed for a good reason. In 2003, an object farther out in the Kuiper Belt than Pluto was discovered. It became known as Eris, and crucially, it's almost the same size as Pluto. Those who still maintain there are nine planets in the solar system are, therefore, wrong — if you keep Pluto, you must also have Eris. With three slightly smaller Pluto-like objects also found — Makemake, Haumea and Sedna — it’s easy to see why the IAU decided to re-classify Pluto rather than admit a possibly ever-increasing roster of new objects to planet-status.
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