What is happening in the confines of our solar system? Is there a planet 9?
In the frigid expanse of our system, there are bodies on orbital trajectories that make no sense with regard to our solar system on eight planets. There seems to be an unknown body, several times more massive than the Earth, shaping the orbits of certain objects in the Kuiper Belt (KBO) and pushing astronomers to examine more closely and more deeply the extremities of our system.
What they are looking for is the ninth planet, mysterious and so far unproven.
The attempt to understand our solar system is one of our oldest quests, and although our catalog of objects in the inner solar system is quite complete, our knowledge of the outer system is anything but complete. For astronomers, observing the details of the external system is always discouraging. But they continue to work there. And the more they observe the behavior of distant objects in the Kuiper Belt, the more they prove that they dig up for Planet 9.
"Understanding the large-scale architecture of the solar system embodies one of the oldest areas of humanity and ranks among the great challenges of the natural sciences."
from the study "The Planet Nine Hypothesis" by Batygin et. Al. 2019.
The history of the planet 9
The story of Planet 9 began in earnest in early 2016, when astronomers Mike Brown and Konstantin Batygin published an article entitled "Evidence of a distant giant planet in the solar system" (previously referred to as other undiscovered planets). most of the time, tin brigade chatter about "Nibiru" or "Planet X". But the less we talk about it, the better it is.)
In their 2016 article, Batygin and Brown have shown that there are KBO groups whose orbits are shaped in such a way that only the presence of another planet can explain them: Planet 9. While the most KBOs clearly show a Neptune orbit, a large number of extremely remote KBOs do not. Their orbits seem to be aligned at a distant point.
In this paper, the authors discuss this discrepancy by stating, "We find that the observed orbital alignment can be maintained by a distant eccentric planet whose mass is greater than about 10 Earth masses, whose orbit is located approximately in the same plane as those of the distant Kuiper belt objects … "
Their paper was partly based on the presence of Sedna, a minor planet first sighted in 2003. Its aphelion, or the farthest distance from the Sun, exceeded 900 astronomical units (AU). At the time, Sedna was the coldest and furthest object. that we know in the solar system. Sedna's elongated orbit has been explained for the first time due to the gravitational influence of Neptune. The problem is that it never approaches enough of Neptune.
But Sedna was only the beginning. This is a group of objects called Extreme Trans-Neptunian Objects (eTNO). Finally, more of these distant objects have been discovered.
"Biden" or 2012 VP 113 was discovered in 2012. "Goblin", or 2015 TG 387, was discovered in 2015. Then in 2018, astronomers discovered "FarOut", or 2018 VG18. Each of these objects is more and more distant.
Recently, in fact, astronomers have discovered what they jokingly call FarFarOut. We do not know much about this planet yet, but it is the farthest object ever detected in our solar system.
How they find evidence for the planet 9
Most of the distant bodies evoking the existence of planet 9 were discovered while an astronomical team led by Dr. Scott Sheppard of the Carnegie Institute for Science was actually looking for the planet 9. Of course, they did not find the hypothetical planet. again, but they continue to find more evidence.
These objects are extremely weak and difficult to detect. The work to find them is done largely by computer. Powerful telescopes target parts of the sky for a while and exposures are taken minutes apart. But it generates a huge amount of data. far too much for astronomers to cover.
Instead, his computers do a lot of routine work. Astronomers use algorithms to allow the computer to search for moving objects on a background of stars. When the computer finds one, it reports it. Then, the astronomers take a look and see if the computer was right. They then make follow-up observations to confirm the results.
New evidence for the planet 9
"Planet Nine's research is already in full swing and it is likely that if Planet Nine – as envisioned here – exists, it will be discovered in the next decade."
from The Planet 9 Hypothesis, Batygin, Brown, Adams and Becker, 2019.
Two new studies now bring us new evidence to support Planet 9.
The first is entitled "Orbital Grouping in the Far Solar System" by Konstantin Batygin and Michael Brown, the couple of astronomers who first proposed the existence of Planet 9. The second is entitled "The Planet 9 Hypothesis", also of Batygin and Brown, with Fred Adams and Juliette Becker, both of the University of Michigan.
In the first article entitled "Orbital Clustering in the Remote Solar System", the authors reject the challenge. They argue that there is a planet 9 shaping the orbits of distant objects or a bias of observation at work. They sought to understand what observation biases might be involved and then quantify them in a rigorous way.
As noted earlier, remote objects that refer to Planet 9 share common orbital characteristics. This is the subject of this whole story of Planet 9. To be more precise, their longitudinal perihelions are grouped together and what we call their polar orbital positions are also grouped together. In the article, the authors conclude that there is only a 0.2% probability that this is random. As they say in their article, "… the statistical significance of this grouping is now hard to dismiss."
The second document providing new evidence for Planet 9 is simply called "The Planet 9 Hypothesis."
In this article, the authors again explain that while much of the orbital behavior of objects distant from the Kuiper Belt is easy to explain and predict in terms of the solar system on eight planets, some are simply not. Specifically, they indicate "an observed physical grouping of orbits with semi-major axes greater than? 250AU, the perihelion detachment of some objects from Neptune's Kuiper belt, as well as the dynamic origin of highly inclined / retrograde long-term orbits. In short, things simply do not make sense if we limit ourselves to our Solar System of eight planets to explain them.
In the introduction, they remind us that only in the last two decades have we started to find all the smaller bodies on the periphery of the solar system. As they say in the newspaper, "… the last quarter century has witnessed the discovery and characterization of a diverse collection of small icy objects residing in the confines of our solar system …". And while most bodies conform to the influence of Neptune and the other planets, others do not.
"The most extreme members of this population, however, trace very long orbits with periods measured in millennia and display a number of curious orbital patterns," explain the authors. Again, this is what the authors call "the striking alignment" of their eccentric orbits, the common inclination of the orbital planes and the "perihelion distances that far exceed Neptune's gravitational range," which call for explanations. .
This method of inferring the existence of a planet by its gravitational effect on other bodies, before observing the planet itself, has already been tried. He was able to discover Neptune, but failed when he predicted the existence of another star project called Nemesis.
So, what extends these objects to perihelias so far? They say that only an extremely remote and massive planet can explain all this: Planet 9. Much of the paper explains how Neptune was discovered by observing the movements of other bodies, in parallel with the Planet 9 hypothesis. They also reviewed some earlier suggestions from other astronomers that another planet might be hidden in the solar system, which would shape KBOs' orbits.
With each paper, and with each new discovery of a distant KBO with strange orbital characteristics, the case of Planet 9 becomes stronger. But direct observation is still the golden rule and until now, this has escaped us. But maybe not for long.
In the conclusion of "The Planet 9 Hypothesis", the authors state: "The search for Planet Nine is already in full swing and it is likely that if Planet Nine – as envisaged here – exists, it will be discovered during the next decade. "
There may be another explanation of the orbits of these distant bodies that does not require planet 9. An article published in January 2019 entitled "Keeping your feet in a self-gravitating disc of trans-Neptunian objects" suggests that a group of icy bodies could cause the strange orbits of these distant worlds, and that a ninth planet is not needed to explain them.
The discovery of planet 9 would be a major triumph for astronomers. The pace of discovery of new objects in the Kuiper Belt accelerates. With the introduction of newer and more efficient telescopes, and the development of improved computers and algorithms, it will be increasingly difficult for a planet, especially a planet that could represent 10 times the mass of the Earth.