Theoretical planet 9 could be a rogue planet not native to our solar system

This site can earn affiliate commissions from the links on this page. Terms of use.

In the nearly 12 months since scientists first proposed the theoretical existence of a “Planet 9”, we have seen several rounds of information and fact-checking. Last year, scientists reported that unusual orbital patterns in several Kuiper Belt (KBO) objects could be explained by the influence of a single larger planet well beyond Neptune’s orbit. . Subsequent refinements to this theory set size limits and theoretical orbital models for any hypothetical planet. If it merged around Sol, Planet 9 is almost certainly an ice giant, smaller than Neptune, and so far from our sun that it could take 10,000 to 20,000 years to complete a single orbit. Neptune and Pluto are both speed demons in comparison, completing one orbit every 164.8 and 248 years, respectively.

According to scientists, there is another interesting possibility: Planet 9 might not originate from our solar system at all. Instead, it could represent what is sometimes referred to as a “rogue” planet, or a planet wandering the cosmos rather than being in a stable orbit around a companion star. Despite the term, rogue planets are considered relatively common, possibly outnumbering planets that orbit the stars. So far only a handful of good rogue planets have been identified, but we have located at least two objects that could fit the definition – CFBDSIR 2149-0403, one object containing no Following over 13 masses of Jupiter (making it a Jupiter-sized planet or a lower brown dwarf candidate) and PSO J318.5-22, with estimated cloud temperatures exceeding 800C despite the complete absence of host star.


Infographic by

We bring up these two candidates because the data available on them suggests two very different planets – and illustrates that whatever Planet 9 is, it could be fascinating and weird. If you’re wondering how a rogue planet can stay hot without a star, but simultaneously fail to appear in the infrared, scientists have been researching this topic. Under the right conditions, a planet that forms with a sufficiently thick atmosphere could retain its internal heat, even in the absence of the sun. The Earth, after all, remains geothermally active despite the fact that no sunlight hitting the planet’s surface is transferred as heat to the planetary core. If a rogue planet had an associated geodynamo and magnetosphere, it would help protect the upper atmosphere from being torn apart as the planet exited its original solar system or from being slowly eroded over hundreds of millions of years. The same insulating tendencies that could trap heat on the surface of these worlds would also make them unlikely to manifest through infrared telescope.

Research into whether Sol could have captured a rogue planet of the theorized size and structure of Planet 9 indicates that it could, according to In most cases, a rogue planet entering our system would spin again, possibly dragging one of our own native planets with it. In about 40% of cases, however, the thief could be captured, either without disrupting the orbits of the planets closer, or by starting one of our own planets in the process. Which of these scenarios exactly depends on the parameters of the experiment, and it is also possible that planet 9 does not exist or does exist but formed in our sun’s orbit like other known planets. Since any rogue planet larger than Neptune would likely have disrupted the orbit of the inner planets, the simulations suggest an upper limit on the theoretical size of Planet 9 that matches other predictions. The hypothetical orbit of Planet 9 is consistent with a rogue planet that Sol captured, but the most likely orbits do not require a thug – they just allow one.

Finding a new planet within the confines of our solar system would, of course, be a momentous opportunity. Find a planet in our solar system that formed around another Star would be one of the most important scientific discoveries in history. Our ability to explore other worlds via a probe or manned mission is currently limited to our own solar system. A rogue planet in our system would represent a phenomenal research opportunity to explore how planetary formation takes place in other star systems, and close examination of the rogue might even give us clues as to which star system it may have originated from.

Of course, this all depends on whether Planet 9 exists in the first place, and we have to find the thing before we can seriously speculate on its origin. Scientists are expected to step up research in 2017.

Arline J. Mercier

Leave a Reply

Your email address will not be published.