It is as if history repeats itself, the history of Urbain Le Verrier. The problem is that this one has two very different endings. In 1846, this French astronomer showed mathematical calculations in which he predicted the existence of a planet beyond Uranus . The orbit of the latter did not match what was expected, and could only be explained if the influence exerted by another unknown celestial body was taken into account.
Using Le Verrier’s data, another astronomer, the German Johann Gottfried Galle, managed to capture an object from the Berlin Observatory on the night of September 23-24 of that same year. It was Neptune, and it was the first time that a planet had been discovered on paper rather than peeking at it. This is one of the endings of the Le Verrier story. The happy ending.
170 years later, in 2016, Mike Brown, an astronomer at the California Institute of Technology (Caltech), in the United States, and responsible for having removed Pluto from the catalog of the planets in the Solar System, published an article with his colleague Konstantin Batygin in which he predicted the existence of another world in the confines of our galactic neighborhood. For Brown it was the only way to explain the orbits of objects in the so-called Kuiper belt, a region located more than 4,500 million kilometers from the sun king. As with Le Verrier, a search began, that of the so-called Planet Nine . Time will be in charge of telling us if with a happy ending or not.
“My bet is that we will find him within three years,” Brown predicts VERY in an interview. He has worked intensively since the publication of that first essay to try to elucidate where that world would be found and what its characteristics would be.
“Batygin and I have made some predictions based on the influence it exerts on other objects in the system,” Brown explains. And he adds: “Multiply by six the mass of the Earth; and it is very far away, about four hundred times the distance between the Sun and the Earth. It has an elliptical orbit, inclined about 17 degrees. Right now, you may be in the farthest part of it. In fact, we know a lot about it, but not enough to simply point to a specific area of space and see it. “
However, Brown believes that perhaps it has already been observed . “It always happens this way,” he says. In essence, there are two ways to find a planet when its existence is suspected, and Brown and Batygin have both set them in motion. “One consists of searching blindly, that is, searching the sky and hoping to be lucky; the other is to take all the data already collected and carefully analyze it. As much as you want to, you cannot focus on a single point, but you can focus on at least one strip, and that is where we are looking, based on information provided by a handful of telescopes. I trust that we will find it sooner like this ”.
Brown recalls that when Pluto was found in 1930, it turned out that it had already been captured fourteen years earlier. “The same thing happened with Uranus. Before his discovery there were already descriptions of him; the oldest is from 1690. Galileo himself saw Neptune – although he thought it was a star – and it also happened to us when in 2003 we discovered Eris , the most massive dwarf planet. We found images of him from 1955, which had also been collected with the same telescope that we used to detect it ”, he tells us. “We take advantage of the confinement to analyze in detail the stored information and try to find it there”
The history of Planet Nine began for Brown in 2014. That year, astronomers Scott Sheppard and Chad Trujillo discovered the 2012 VP113 object, whose orbit was the most distant known in the Solar System. In addition, they found that known trans-Neptunian objects in the Kuiper belt showed very similar orbital angles. This led them to predict the possible presence of a planet more than two hundred times the distance from Earth to the Sun.
“It was a very exciting prediction, but I was skeptical. Most astronomers dismissed the idea out of hand as wrong or controversial, but I knew Trujillo and Sheppard. They are astronomers who know what they are doing, and if they said something like that it must be for a good reason, “recalls Brown.
After reviewing the calculations with Batygin, he realized that there were even other phenomena that had gone unnoticed and that could be caused by the existence of that hypothetical new world. However, they decided not to announce it for the time being.
“We spent about a year trying to show that this body could not be there. Almost the day after Neptune was found, people began to say that there must be another planet beyond it, so we didn’t want to say such a thing just like that, ”explains Brown. But the more time passed, the more it seemed to confirm that, indeed, the observed phenomena could only be explained by the presence of Planet Nine.
There are many elements that come together in this story and they all end up orbiting Brown. In his article The Planet Nine hypothesis , published in 2019 in Physics Reports , this astronomer and his collaborators indicate that “ the search for new planets in the Solar System has been surprisingly inefficient : only two large objects have been discovered that were not known to the ancient civilizations – Uranus and Neptune – and there have been no significant updates to the system catalog since 1930 ”.
In the middle of that year, Clyde Tombaugh found Pluto from the Lowell Observatory in Flagstaff, Arizona. It was considered the ninth of the planets, but Brown himself would end up removing it from that list. He tells it himself in his book How I Killed Pluto and Why It Had It Coming (How I killed Pluto and why he deserved it), 2010. Well, now he is the one who is looking for Planet Nine.
The aforementioned Flagstaff observatory had been built by Percival Lowell, a member of the Boston cultural elite of the time and, in a way, heir to Le Verrier. Lowell spent half his life traveling through Europe and the Middle East, and at the age of 39 he set out to build that facility to demonstrate an occurrence that made him famous: according to what he claimed, canals were preserved on Mars that would have been built by an alien culture.
When it became clear that this had not happened, Lowell, who had studied at Harvard and had excellent marks in mathematics, tried to calculate the location of a possible ninth planet in our system.
According to the scientific popularizer Dava Sobel in Los planetas (Anagrama, 2006), “too many discrepancies that still disturbed the orbit of Uranus suggested that the spectacular milestone of Le Verrier and Adams –John Couch Adams had also predicted the existence and position of Neptune– in the previous century it could be repeated, on American soil, to find a new world beyond Neptune ”. Lowell called it Planet X , the search for which he devoted himself boldly, but without success, until his death in 1916.
Sobel says that his widow blocked the activity of the observatory for more than ten years until in 1929 he hired an amateur astronomer: Clyde Tombaugh. It only took a few months for it to discover Pluto. However, something did not add up: Lowell had calculated that his Planet X would have a mass several times that of Earth, enough to affect the orbits of Uranus and Neptune; and Pluto did not meet this requirement. It was too small.
Things stayed that way until 1951, when Gerard Kuiper predicted that there must have been a plethora of icy bodies beyond Neptune when the Solar System formed. In this way, he was trying to explain where short-period comets came from. It was a conjecture, since no one had been able to see anything in that region, although Tombaugh had unknowingly already observed it. The technology to distinguish the so-called trans-Neptunian objects that make up the Kuiper belt simply did not yet exist.
In 1992, David Jewitt and Jane Luu managed to observe the first, with a telescope installed on the Mauna Kea volcano, in Hawaii. They called it 1992 QB1. With it, the belt began to be a reality and our image of the Solar System was going to shatter. The discoveries in that area immediately began to occur. And this is where Mike Brown comes into this story.
On November 14, 2003, Brown discovered a trans-Neptunian object he named Eris, whose mass even exceeds that of Pluto. Moreover, little by little, other similar bodies began to appear. So either the hand was opened unceremoniously and the number of planets increased, or drastic measures were taken. It was thus that on August 24, 2006, 424 scientists belonging to the International Astronomical Union voted in Prague to exclude Pluto from the first division and introduce it into a new category, that of dwarf planets, in which Eris, Makemake, are also present today. Ceres and others.
The Solar System thus once again had eight major planets, but something still did not add up. The aforementioned article by Trujillo and Sheppard put Brown and Batygin on the trail of another possible world. Two years later, in 2016, the Caltech astronomers published their own essay, in which they provided new evidence and even tried to calculate the probability of error in their claims: in their opinion, there was 0.007% that the orbital grouping of the elements of the Kuiper belt were the product of chance. In 2019, in another joint article, Brown and Batygin estimated that there was only a 0.2% chance that such a phenomenon was due to observational noise.
With this, they tried to stand up to the most critical colleagues, who argued that mathematical calculations are one thing and direct observation of objects is another. It may be that both things do not go together perfectly, as the detractors of Planet Nine argue, but this would be more due to the difficulty of fitting reality to a mathematical model that could hardly include all the existing elements. If the skeptics were right, the search for Planet Nine would meet the same fate as Vulcan.
Vulcan is the other offshoot of Le Verrier’s story, that of the unhappy ending. The French astronomer not only set out to accurately predict the existence of Neptune, but also ventured, pencil and paper in hand, to conjecture the existence of a planet around Mercury, due to a dysfunction in its orbit. He called him Vulcan, but he never appeared. To try to calculate his position, Le Verrier could only make use of Newton’s law of universal gravitation. He died in 1877 without knowing anything about his planet, and it was not until much later that the mess was resolved. In the second decade of the 20th century, Albert Einstein made his theory of general relativity known, which allowed us to verify that the problem was not in Mercury, but in Newton’s postulates.
Over the years, Brown and Batygin’s prediction has been gaining popularity among astronomers, although it is not a word that Brown likes. “Those who have thoroughly analyzed all of our data and calculations have been convinced. The rest of the scientific community has wisely taken a skeptical attitude ”, points out this researcher. And he adds: “After all, so far, all the times that the existence of a planet beyond Neptune has been proposed has turned out not to be the case. It is normal that when we announced it they thought ‘okay, yes, again’, but I think that now most of them are simply waiting to see if it ends up being discovered or not ”.
Brown tells us about the moment when he knew he had to be there: “I was sitting in my office, in front of all the computer simulations we had to show not only that Planet Nine was the cause of all the effects that we had observed, but which also explained the existence of the entire population of objects on the periphery of the Solar System that we had studied earlier. If we hadn’t seen it, we would have thought we were wrong. But the rest of the objects were exactly where we had predicted ”. That was about six years ago. “Since then, everything that has been discovered in that area of the system points to the existence of Planet Nine,” says Brown.
The discovery of the Kuiper belt, whose presence the appearance of Pluto gave us the first clue, revolutionized the image we had of our galactic neighborhood. That revolution can take a giant leap if Planet Nine is finally detected. However, progress in the search for objects in the outer reaches of the Solar System has so far been slow. Why? “It’s a technology issue,” explains Brown. “Pluto was glimpsed at the time because it is relatively close to the Sun, which also makes it one of the brightest distant objects. But the next one that appeared in the Kuiper belt could only be observed when digital CCD cameras became available ”.
Observational technology may also be the key to the sighting of Planet Nine. The Caltech astronomer recalls how he got his first digital camera in 1995. It was a machine of only 400 x 600 pixels, but it allowed him to start looking in smaller and smaller portions of the sky. “The great innovation came when towards the end of the last century increasingly advanced devices became available. In 2002, we were able to put 112 digital CCD cameras together, as if it were a single much larger one. Thus, we managed to cover tiny areas of the sky. However, it takes about five years to be able to track everything down, ”says Brown. In this way, objects began to appear in the Kuiper belt, too small to see with the previous technology, and to populate the Solar System beyond Neptune.
Brown believes that if Planet Nine does not appear among the data and observations already made, it may be brought to light by the future Vera C. Rubin Observatory, which will start operating in 2023 , in northern Chile. “We have delimited a strip in the sky in which it could be found. If we do not find it in the next three years among the information we already have, it is surely due to the fact that it is in the most diffuse area of that strip. If so, the Vera C. Rubin will do so even in its early exploration phases. It is a much more powerful telescope than the ones we have used so far ”.
When it is located, other devices will be aimed at it, such as the James Webb space observatory, which NASA plans to launch later this year. “It is one thing to scan the sky and another to focus on a very specific area. These types of devices are very good at the latest, ”says Brown. And remember: “However, the problem is not so much to glimpse an object in a remote area of the Solar System, but to locate it. Imagine that I show you a grain of sand. It is very easy to see it, but if I throw it on the beach and ask you to look for it, it will take time ”.
When Planet Nine is the target of all available telescopic artillery, we can learn more about it and, consequently, about our galactic neighborhood. The main doubt that will be resolved is its own nature. “There are two options. It could be a rocky body, like Earth; then it would be really great. Or maybe it’s gaseous, like Neptune, which is seventeen times the mass of our planet. In that case, it would be a small version of that one. I bet on the latter, “ adds Brown.
“It probably formed around Uranus and Neptune; later, it may have circled very close to Saturn. Perhaps for this reason he was expelled to the position he now occupies. It is not a crazy idea. In the last decade, data has been collected on some fifteen or sixteen giant planets that would have been ejected like this ”, he emphasizes.
Another option Brown is contemplating is for Planet Nine to be snatched from a star passing close to the Solar System, although he admits it’s complicated. “The third possibility is that it was born directly where it is. We do not know how such a thing could have happened, but just because we think that something is impossible does not mean that it could not have happened, “he says.
Furthermore, Brown is convinced that this story will not end with Planet Nine. “I explain it to the young people who come to my lectures. I make it clear to you that my generation of astronomers and the current technology available will take care of it. But it will get better, and those guys, the future astronomers, will have to deal with the Ten, the Eleven and the Twelve. “
Because there will be more worlds , says Brown. Of course, they will not be called that. In fact, Planet Nine is a catch name we use while searching. “We haven’t thought about it out of sheer superstition,” he jokes. “When we find him, he will receive one, but if we put it on before we find it, we will surely not find it.”
