Is there another planet in the Solar System? – Magazine ?

In January 2016, astronomers Mike Brown and Konstantin Batygin announced that they had found indirect evidence of the existence of a new planet in the Solar System. It was not a small, icy world like Pluto, but a body up to 10 times the mass of the Earth and the size of Neptune, but there is still no direct evidence of its existence.

Thousands of years ago, five celestial bodies were already known that were not fixed in the sky like the stars. They were called planets, from the Greek word meaning “wanderer.” They were Mercury, Venus, Mars, Jupiter and Saturn, a list that Earth joined over the course of the 17th century.

In 1781 William Herschel discovered a seventh planet using a telescope (Uranus), and in 1846 Neptune, the eighth planet in the Solar System, was discovered based on the irregularities in the movement of Uranus, which made astronomers think that something was happening to it. gravitational pulls.

Since then, small deviations from the expected motion of one planet became clues to the existence of another. After the discovery of Neptune, astronomers wanted to see evidence of a planet very close to the Sun in the anomalies of Mercury’s motion. They called him Vulcan. Today we know that Vulcan does not exist. Mercury’s irregularities are explained by the general theory of relativity.

The ends of the Solar System

In 1906, the industrialist and amateur astronomer Percival Lowell became convinced that another unknown planet, in addition to Neptune, was causing anomalies in the orbit of Uranus. He named it Planet X, but at his death in 1916, he had not yet found it. In 1930, astronomer Clyde Tombaugh discovered a new planet, which he named Pluto. Although Tombaugh initially believed he had found Lowell’s Planet X, in reality Pluto is too small to have gravitational influence on Uranus.

Since its discovery, astronomers had considered Pluto the lone inhabitant of the vast space beyond Neptune. However, since the 1990s, many bodies with diameters ranging between 10 and 1,000 kilometers have been discovered in a region known as the Kuiper belt. The name refers to Gerard Kuiper, a Dutch astronomer who in 1951 theoretically predicted its existence and suggested that some comets have their origin in that region.

Today more than 1,500 Kuiper Belt objects have been sighted at distances between 30 and 100 astronomical units and it is suspected that there may be billions. An astronomical unit, or AU, is the average distance between the Sun and Earth, about 150 million kilometers. Neptune is located about 30 AU from the Sun. Kuiper Belt bodies (or trans-Neptunian objects) were ejected from the vicinity of the Sun into this remote outer region when the planets rearranged themselves into their current orbits and are considered relics of the formation of the Solar System, about 4.5 billion years ago.

The Solar System does not end at the Kuiper Belt. In 1950, Dutch astronomer Jan Oort proposed that long-period comets (more than 200 years) come from an even more distant region, today called the Oort cloud. Located almost a light year away from the Sun (more than 63,000 AU), it is a cold and dark region. The objects that make it up possibly number in the hundreds of millions, despite which any two of them will be millions of kilometers apart. Although no one has observed it, scientists estimate that the Oort cloud is the border of the Solar System. Beyond this region, the gravity of other stars in our galaxy dominates the Sun’s gravity.

Red herrings

The search for Planet X did not end with Pluto. In 1999, British astronomer John Murray announced that he had found evidence of the existence of a new planet by studying irregularities in the orbits of 13 comets. According to Murray, the new planet was several times larger than Jupiter, was 1,000 times farther from the Sun than Pluto and took six million years to complete an orbit around our star. Rejected by prestigious magazines Nature and ScienceMurray managed to publish his hypothesis in the monthly newsletter of the Royal Astronomical Society from the United Kingdom, but it has never been proven.

That same year, astronomers John Matese and Daniel Withmire, from the University of Louisiana, proposed the existence of a gigantic gas planet located in the Oort cloud. The planet, as large as Jupiter and four times as heavy, was nicknamed Tyche, after the Greek goddess of fortune and prosperity. According to Matese and Whitmire’s estimates, the planet Tyche should have been captured by NASA’s WISE telescope, which completed an all-sky infrared survey in 2012. However, there has been no luck on this occasion either, and no trace of Tyche has been found among the WISE mission data.

Too much coincidence

The story of the most recent attempt to find Planet . They named him Sedna, goddess of the sea in Eskimo mythology, condemned to live in the cold depths of the Arctic Ocean.

Sedna has several peculiarities that made it unique at that time. Its orbit, very elongated, was unlike any other. At its furthest point from the Sun it is incredibly far away, at 930 AU. At its closest point it is 76 AU (more than twice the distance of Neptune) and it is estimated that Sedna takes about 11,400 years to complete one revolution around our star. This orbit is similar to that of long-period comets, whose origin is in the distant Oort cloud, and which suffer the influence of the giant planets (Jupiter, Saturn, Uranus and Neptune) as they enter the Solar System. Sedna, on the other hand, is in the middle of nowhere: too close to belong to the Oort cloud, too far to feel the influence of the giant planets. In other words, no one knows how it got there.

Years later, it became clear that Sedna’s orbit was not so special. In 2012, astronomers discovered another celestial body with a very similar orbit. They called it 2012 VP113. Soon four other objects were added, and there were six in total Kuiper belt bodies with very elongated orbits. The similarities do not end there: it turns out that the six orbits have perihelion – the point of closest approach to the Sun – in the same region of space and are also practically in the same plane.

Could all this just be coincidence? According to calculations, the probability of this being due to simple chance is 7 in 100,000, the same as the probability of obtaining the same result 14 times when flipping a coin. And if the influence of the giant planets were responsible for this situation, computer simulations showed that the trajectories would have become disordered again in a very short period on the cosmic scale. Everything indicates that something is currently holding their orbits together.

A needle in a cosmic haystack

Mike Brown thought it was time to recover the Planet Brown and Batygin began by wondering if a planet might exist in a very distant orbit that would encompass the orbits of the six wayward celestial objects and force them to stay aligned with its cosmic embrace. The idea was discarded, since it did not accurately give the observed orbits. The same thing happened with other hypotheses they tested, until they finally found one that made all the pieces of the puzzle fit together. The solution was a planet the size of Neptune, perhaps a little smaller. Its orbit had to be such that when the other objects are closest to the Sun, the hypothetical planet would be at its furthest point, and vice versa. The orbit of the so-called Planet Nine would also be very elongated, since in no case would it approach less than 200 AU from the Sun, and could move away up to a whopping 1,200 AU. With these data, the new planet would take about 15,000 years to complete one revolution around the Sun.

As an added surprise, Brown and Batygin’s simulations predicted the existence of a new colony of Kuiper Belt objects with orbits perpendicular to that of Planet Nine. Well, although both scientists were unaware of it at the time, there are at least five known objects with this characteristic, which significantly reinforces the hypothesis of the two Caltech astronomers.

If the existence of Planet Nine seems so certain, why haven’t we seen it until now? The main reason is that, if it exists at all, it is too far away. Wherever Planet Nine is located, the Sun is just another star in the sky, little brighter than the rest. Data from NASA’s WISE infrared space telescope have ruled out the existence of planets the size of Saturn up to a distance of 10,000 AU, or the size of Jupiter up to 26,000 AU. But Planet Nine would be smaller and could have gone unnoticed. On the other hand, telescopes sensitive enough to detect such small and distant bodies, for example Hubble, have extremely small fields of observation. Discovering Planet Nine with them is similar to finding “a needle in a haystack looking through a straw,” as the magazine states. Science.

Well-founded hypotheses

Although we are still not sure of its existence, we can ask some interesting questions about Planet Nine. For example, how would it have been formed? The most solid hypothesis is that Planet Nine would have been born very close to the Sun and then be expelled to the confines of the Solar System due to gravitational interactions with the other four giant planets. In fact, several models of the formation of the Solar System, such as the so-called Nice Model, already predicted that five giant planets originally formed around the Sun. One of these, precisely with the mass of Neptune, ended up being expelled from the Solar System after passing close to Jupiter, which would have allowed the rest of the giant planets…