On January 20, 2016, scientists Konstantin Batygin and Michael Brown of the California Institute of Technology announced that they had found evidence of a massive planet at the edge of the solar system. Based on mathematical and computer simulations, they predicted that the planet would be super-Earths, two to four times the size of Earth and 10 times more massive. They also calculated that given the planet's distance and its extremely elongated orbit, the planet orbits the Sun in 10,000–20,000 years.
Since then, many scientists have responded with their own research about the possible existence of this mysterious "ninth planet", as it was temporarily dubbed. One of the most recent studies was conducted at the University of Arizona. Scientists have shown that the extreme eccentricities of distant Kuiper belt objects may indicate that they have intersected with a massive planet in the past.
By that time, it was already known that there are several objects in the Kuiper belt, the dynamics of which is different from others. While most of them are subject to the gravity of the gas giants in their current orbit (such as Neptune), some members of the scattered disc of the Kuiper belt population have unusually close orbits.
When Batygin and Brown first announced their find in January, they noted that these objects were strongly grouped in relation to the positions of their perihelions and orbital planes. Moreover, their calculations showed that the chances of such an arrangement being formed by accident are extremely small (the probability was estimated at 0.007%).
Instead, they suggested that a distant eccentric planet was responsible for determining the orbits of these objects. For this, the planet must be ten times more massive than the Earth, and its orbit must lie in the same plane (but with a perihelion 180 degrees deflected from the perihelion of objects).
Such a planet not only offers an explanation for the presence of highly perihelial Sedna-like objects, that is, planetoids with extremely eccentric orbits around the Sun. It also helps explain where distant and heavily deflected objects from the outer solar system come from, as their origins remain unclear to this day.
In their work, University of Arizona scientists - including Professors Renu Malhotra, Dr. Katrin Volk, and Jiang Wong - took a different perspective. If the ninth planet did intersect with certain highly eccentric Kuiper belt objects, they speculated, chances are high that its orbit is in resonance with these objects.
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So, small bodies were constantly thrown out of the solar system due to encounters with large objects that violated their orbits. To avoid ejection, small bodies must be protected by orbital resonance. And although these small and large objects can cross orbital paths, they never get close enough to have a powerful effect on each other.
This is how Pluto remained part of the solar system, despite having an eccentric orbit that periodically crosses the path of Neptune. Although the orbits of Neptune and Pluto intersect, they never get close enough for Neptune's influence to push Pluto out of the solar system. For the same reason, scientists have suggested that the Kuiper Belt objects noted by Batygin and Brown may be in orbital resonance with the ninth planet.
In a letter to Universe Today, Malhotra, Wolf, and Wong recounted the following:
“The Kuiper belt objects that we have studied in our work differ from others because they have very distant and very elongated orbits, but their closest approach to the Sun is not close enough to be significantly affected by Neptune. Thus, we have six of these objects, the orbits of which are slightly influenced by the known planets of our solar system. But if in several a. That is, there was another planet from the Sun, not yet discovered, it would affect six of these objects."
Having studied the orbital periods of a number of objects - Sedna, 2010 GB174, 2004 VN112, 2012 VP113 and 2013 GP136 - they concluded that a hypothetical planet with an orbital period of 17,117 years (with a semiaxis of 665 AU) must necessarily have periodic relations with these objects. This fits the parameters of 10,000–20,000 years of the orbital period that Batygin and Brown talked about.
Their analysis also makes assumptions about what kind of resonance the planet has with the designated objects. The orbital period of Sedna should be in resonance with the planet at 3: 2, 2010 GB174 - 5: 2, 2994 VN112 - 3: 1, 2004 VP113 - 4: 1, 2013 GP136 - 9: 1. Such a resonance simply could not have formed in the absence of a large planet.
“For a tangible resonance to appear in the outer solar system, one of the objects must have a mass that could have a strong gravitational effect on the other,” the scientists write. "Unusual Kuiper belt objects are not massive enough to resonate with each other, but the fact that their orbital periods fall in the region of simple relationships may mean that they are in resonance with a massive invisible object."
Particularly encouraging, their findings may narrow the range of possible locations for planet nine. Since each orbital resonance provides a geometric connection between the bodies involved, the resonant configurations of these objects can help astronomers find the right points in our solar system to search for.
But, of course, Malhotra and her colleagues openly admit that several unknown variables remain and further observation with research is needed to confirm the existence of the ninth planet:
“There are quite a few uncertainties. The orbits of these extreme Kuiper belt objects are not well known because they move very slowly in the sky and we observe only a small fraction of their orbital motion. So their orbital periods may differ from current estimates, and some of them may go out of resonance with a hypothetical planet. There is also the possibility that the orbital periods of these objects are related; we have not yet observed many such objects and we have limited data."
Astronomers and we will await further observations and calculations. But in the meantime, we must admit that the possibility of the existence of the ninth planet is very intriguing. Perhaps, in the ranks of the planets of our solar system, there will again be all nine fighters (sorry Pluto).