Ever since the possibility arose that a large ninth planet could orbit somewhere beyond Neptune, astronomers have been busy looking for it. One of the teams is studying four new moving objects found by members of the public to see if they could be new potential discoveries of the solar system. Most interestingly, these scientists have found something that could question the entire prospect of a ninth planet.
One of these finds was the discovery of a minor planet in the outer solar system: 2013 SY99. This small icy world has such a distant orbit that it takes 20,000 years for one long, looping passage. We discovered SY99 with the Canada-France-Hawaii telescope as part of our survey of the origin of the outer solar system. The long distance to SY99 means that this small planet is moving very slowly across the sky. Our measurements showed that the orbit of the body is a very elongated ellipse with the closest approach to the Sun in 50 astronomical units (1 AU is the distance from the Earth to the Sun).
The new minor planet is zigzagging even further than previously discovered dwarf planets such as Sedna and 2013 VP113. The long axis of its orbital ellipse is 730 astronomical units. Our observations with other telescopes have shown that SY99 is a small, reddish world about 250 kilometers in diameter.
SY99 is one of seven known minor worlds that orbit significant distances beyond Neptune. How these "extreme trans-Neptunian objects" are located in their orbits is completely incomprehensible: their distant paths are isolated in space. The closest approach to the Sun is so far beyond Neptune that they are considered "separated" from the powerful gravitational influence of the giant planets of our solar system. But at their farthest points, they are still too close to be propelled by the slow streams of the galaxy itself.
It has been suggested that extreme trans-Neptunian objects could be grouped in space by the gravitational influence of the "ninth planet", which orbits much farther than Neptune. The gravity of this planet could pull the planets out and separate their orbits, constantly changing their tilt. But the existence of this planet is far from proven.
In fact, its existence is based on the orbits of only six objects, which are very faint and difficult to find even with large telescopes. It is like looking deep into the ocean for a specific fish. Fish near the surface will be clearly visible. But already at a meter depth everything becomes vague and unclear. Somewhere at the very bottom, the fish become completely invisible. But the presence of fish at the surface makes it difficult to see the fish at the bottom and at the same time does not betray the presence of the latter.
It follows from this that the discovery of SY99 cannot prove or disprove the existence of the "ninth planet". But computer models show that Planet Nine will be an unfriendly neighbor for tiny worlds like SY99: its gravitational influence would greatly change the orbit of such a planet - completely ejecting it from the solar system or pushing it into an orbit so tilted and distant that we would not see it. … SY99 may be one of the many minor worlds that are continually being sucked in and out by this planet.
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Alternative explanation
It turns out that there are other explanations as well. Scientists have submitted a study for publication in the Astronomical Journal in which they raised such an idea from ordinary physics as diffusion. This phenomenon is common in the ordinary world. Diffusion essentially explains the random movement of a substance from an area of high concentration to an area of low concentration - as, for example, the scent of perfume spills over a room.
They showed that a certain form of diffusion can cause the orbits of minor planets to change from an ellipse of 730 AU. That is, along the long axis to an ellipse of 2000 AU. That is, along the long axis or more - and vice versa. In the process, the size of each orbit will change by a random amount. When SY99 approaches its closest distance every 20,000 years, Neptune is often in a different part of its orbit at the opposite end of the solar system. But when SY99 and Neptune get close, Neptune's gravity will gently push SY99, slightly changing its speed. When SY99 moves away from the Sun, the shape of its next orbit will be different.
The long axis of the SY99 ellipse will change, becoming larger or smaller in a "random walk," as physicists call it. The orbit change occurs on truly astronomical time scales. It dissipates in space over tens of millions of years. The long axis of the SY99 ellipse could have changed by hundreds of astronomical units over the entire history of the solar system of 4.5 billion years.
Several other extreme trans-Neptunian objects with smaller orbits also exhibit diffusion, but on a smaller scale. One is followed by others. It is very likely that gradual diffusion effects are acting on tens of millions of tiny worlds orbiting at the near edge of the Oort cloud (spheres of icy objects at the edge of the solar system). This gentle impact slowly causes some of them to accidentally shift their orbits closer to us, where we view them as extreme trans-Neptunian objects.
Yet diffusion cannot explain the distant orbit of Sedna, whose nearest point is too far from Neptune to influence the shape of its orbit. Perhaps Sedna got her orbit from a passing star a long time ago. But diffusion could bring extreme trans-Neptunian objects from the inner Oort cloud - without any need for a ninth planet. To find out for sure, we will have to try to make more discoveries in this distant region of the nearest space to us. Our largest telescopes will help us with this.
ILYA KHEL
