Our solar system may be closestpart of the universe to us, when viewed from the Earth, but even at its margins we will find many surprises. Several thousand years passed before we understood how the planets revolve around the Sun, and hundreds more before we discovered Uranus and Neptune. Today we have four inner solid planets, an asteroid belt and four gas giants with their satellites and rings.
But outside of Neptune there are many unknowns. There are much more than Pluto, comets and Kuiper belt. The last several decades of searches have revealed completely new classes of objects, including those with mysterious orbits, which are difficult to explain. Some scientists claim that these objects point to the "ninth planet", a hypothetical giant planet that is far beyond what we see. But, despite the fact that we constantly write about it, most scientists have not yet been able to convince of its existence. Perhaps the "ninth planet" does not exist. And that's why.
Ninth planet: myth or reality?
In the early 1990s, scientists discovered the firstan object of the solar system outside of Neptune that was not part of the Pluto system. Since our telescopes became better both in terms of magnitude (and could see fainter objects) and fields of view (the area of the panoramic sky), we got the opportunity to observe more and more objects.
Most of them had orbits similar to Pluto: their closest approach to the Sun puts them relatively close to Neptune. Although Neptune is at 30 AU (1 AU, as you know, this is an astronomical unit, the average distance from the Earth to the Sun) from us, almost all objects outside Neptune are within 50 AU from the sun. All of them are classified as part of the Kuiper belt. Outside of this belt is the “Kuiper cliff”, because the number of objects is rapidly decreasing.
But we found objects that are notpart of the Kuiper belt. Sedna, opened in 2003, was the first amazing object to be on this list. Scientists Mike Brown, Chad Trujillo and David Rabinovich have found a large body 1000 km across. It is now known that Sedna is a dwarf planet. But the most interesting thing during its discovery was in orbit. Coming closer, Sedna is at a distance of 76 AU from the Sun, but at a distance leaves up to 1000 AU from the star.
And she needs more than 10,000 years to completerevolution around the Sun and not be disturbed by Neptune. Somehow, she managed to get such a strange orbit. In the article on the discovery, the authors pointed out the possibility that the cause could be an undetected planet.
In subsequent years, especially in the 2010s, there werefound a large number of these strange objects of the solar system. Trujillo and Scott Sheppard have discovered a small but significant number of these distant trans-Neptune objects (TNOs) that have similar orbital properties. Although thousands of objects can enter the Kuiper belt, there are more than ten objects with these elongated orbits that never come too close to Neptune.
It was Trujillo and Sheppard who first suggested in2014, that the cause of the convergence of these orbits may be a large planetary type object. The orbits of the extreme TNOs discovered in 2014-2016 correlated in properties. Perhaps this correlation was associated with a large, massive object that messed up their movement. In 2016, Konstantin Batygin and Mike Brown called the hypothetical object "the ninth planet."
But this is not an irrefutable statement. Despite the fact that Batygin and Brown analyzed objects that they knew about, and determined that there was a very small probability - 1 in 10,000 - that they would accidentally be located as we found them, there is a big risk that this incomplete data set will lead to a false conclusion. The objects discovered by Trujillo were found in a series of studies that cannot be considered unbiased:
- They could only see a particular stretch of sky.
- They searched for objects with a certain minimum brightness.
- They ignored any objects that came too close to Neptune.
- They searched in the plane of the solar system or close to it.
In other words, and this is the most important missedfact, the studies that provided the strongest allusions to the existence of the ninth planet deliberately underestimated the large class of objects that could cast doubt on the ninth planet hypothesis.
But other studies have led to different conclusions. They used other methods, other telescopes, and selected other parts of the sky. The OSSOS dataset, for example, did not ignore perihelion objects that brought them close to Neptune, and examined approximately 0.3-0.4% of the sky.
When they looked for objects similar to Sedna, theyfound only nine of these. It may seem that this is not very much, but much more than the meager six objects that were known in 2016, when the legend of the “ninth planet” appeared. And when these OSSOS objects were analyzed, it turned out that their orbits were completely random. And no planet was needed.
And from the point of view of physics, this has an explanation. There are four possibilities that could explain not only Sedna, but also a handful of additional extreme TNOs that we have found since then, but which have never come close to the major planets of our solar system:
- Galactic tides could disturb these orbits, slowly stretching some of them and moving closer to Neptune for hundreds of millions of years.
- The approaches of other stars or wandering planets in our galaxy, which pass by our solar system, violated these objects and created these elongated orbits.
- The huge number of dwarf planets in the outer solar system that existed in its early stages gave rise to these extreme TNOs, but have since been ejected to a large extent.
- Or it was the ninth planet (or even two planets - nine and ten), which hid there and pushed extreme TNOs into their current orbits.
As always, we need more data and more qualitative data to solve this mystery of the universe.
Michelle Bannister, one of the leaders of OSSOS, believes that putting an end to the debate about the existence of the ninth planet is quite possible:
“A direct search for evidence will reveal moretrans-Neptune objects during surveys with well-characterized deviations. Dark Energy Survey will study the sky, which is far from the plane of the solar system. "Orbits with large deviations from the plane will thus be in its target range."
If there really was a real big planet outside Neptune, you would expect to find a large number of these objects with highly inclined and very eccentric orbits.
Just a few weeks ago, a new object, likeHe would have strengthened the hypothesis of the "ninth planet", but, apparently, this is another case from the category of "do not rush." This object was discovered during the same reviews and methods as other objects that speak in favor of the “ninth planet”, which means that they are vulnerable to the same errors. On the other hand, other reviews with other deviations do not need a ninth planet at all.
When you have a hammer, everything will look likenail. If you try to search for objects that speak in favor of the “ninth planet” and skip objects that do not support it, this does not mean that you will find this planet; this means that you need better data before you can understand what is really happening. We need not only to search for the ninth planet, but also to study the solar system outside the Kuiper belt as a whole.
New studies, improved sky surveysand better data in total promise to make the next decade of astronomy very interesting. Perhaps we will not only unravel the mystery of what is beyond Neptune, but also understand how the solar system as a whole is formed and evolves.
Or does the ninth planet still exist? Tell in our chat in Telegram.