Our solar system may have a hidden planet beyond Neptune – no, not that one

There are eight recognized planets in our solar system, four inner rocky planets, and four outer gas giants. But beyond Neptune’s orbit, dozens of Pluto-sized dwarf planets or smaller populate an area known as the Kuiper Belt, and new computer models show that there may be something wrong with it. ‘even bigger lurking there – or at least there could have been in the past.

In an article from Annual review of astronomy and astrophysics This month, Brett Gladman of the University of British Columbia and Kathryn Volk of the University of Arizona argue that new models indicate that the likelihood of a planet the size of Mars orbiting the region of the Kuiper Belt is at least 50%, although they also claim that it was fully ejected from the solar system at some point in the past.

It would be a different planet from the theoretical one currently called Planet Nine, which would be a gas giant the size of Neptune well beyond the Kuiper Belt.

To get a better idea of ​​how the solar system was formed, researchers like Gladman and Volk typically use powerful computers to run simulations with different variables to see how changes in one variable affect the type of solar system that would result. In several Gladman and Volks simulations, something like our solar system is formed when there is a rocky ninth planet orbiting the Kuiper Belt.

“I agree that it’s likely that a Mars-class planet was there initially,” said David Nesvorny, a planetary scientist at the Southwest Research Institute. Reverse, “but the question is whether he survived and if we have any evidence of that.”

Other planetary scientists are also finding similar results in their simulations, including Kedron Silsbee, of the Max Planck Institute for Extraterrestrial Physics, and Scott Trmaine, of the Institute for Advanced Study.

In these simulations, the outer planets were not in their original orbits, and sometimes not even in the same order, and the simulations suggest that the gas giants could have benefited from additional assistance in getting to their current positions. .

Another large object in the inner solar system could have been pulled out by the gas giants and eventually pushed to the outskirts of the solar system, or even completely out of it.

“Our simulations revealed that in about half of the cases, all of the Mars-scale planets in the outer solar system were ejected into interstellar space,” Tremaine said. “But in the remaining half, a ‘rogue’ planet was left in an orbit similar to that of the detached population of Kuiper Belt objects.”

Analysis: we really don’t know much about the solar system we live in

We know a lot about the solar system, but sometimes we just don’t know what we don’t know, making it difficult to understand the full history and evolution of our home system.

While the order of the planets, with the four rocky worlds within and the four gas giants on the outer half, may appear to be a natural order, it’s really only because it’s the one we grew up with. as a species.

Now that we have observed other stars and their exoplanets, our solar system is not like most solar systems in the galaxy. A system like ours, with rocky inner planets and large gas giants on the outside, only represent 10% to 15% solar systems there.

Moreover, we don’t even know if we have an accurate census of the planets in our own solar system, with the possibility of a rocky world the size of Mars beyond Neptune or a gas giant the size of. Neptune, the currently theorized planet. Nine, even further than the Kuiper Belt, both being possible planetary candidates.

It may take years, even decades, before we know for sure, if ever. After all, space – even our tiny part – is a very large place.

Arline J. Mercier

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