| Queue of competitors We all know from school textbooks that there are nine planets in the solar system. However, this number may soon change. Either we will reach a full ten, or, conversely, we will shrink to eight. Recently, astronomers were able to approximately measure the size of the trans-Neptunian (beyond the orbit of Neptune) asteroid Xena. It turned out that it is even larger than Pluto. Now scientists have to decide what to do with the status of another overgrown asteroid.
Pluto has long raised doubts among astronomers: it does not really qualify for the status of a large planet. Pluto is too small, its diameter is 2.3 thousand km - it is even smaller than the Moon. When it was discovered, Pluto's size could only be determined approximately by the strength of the light it reflected. As a result, for about 40 years it was believed that Pluto was about the size of Earth, or at least the size of Mars. If this mistake had not been made, perhaps Pluto would not have been considered a planet even then.
Pluto's orbit is also unusual for planets. It is highly elongated, so Pluto sometimes appears closer to the Sun than its neighbor Neptune. Even more unusual for large planets is that Pluto's orbit is inclined at a fairly large angle to the plane in which the orbits of other planets lie.
It seems that Pluto, like a decent planet, even has a satellite. Charon was discovered in 1978. But Charon is indecently large for a satellite, only eight to ten times lighter than Pluto itself. The Moon, for example, is 81 times lighter than the Earth, and is considered a heavy satellite.
So Pluto has always been considered a planet with some stretch. But there were no other large bodies beyond Neptune’s orbit, so Pluto’s status was preserved.
Queue of competitors
Pluto's first competitor, called Chiron, was discovered in 1977. Some were quick to call it the tenth planet. But Chiron is much smaller than Pluto, and its orbit is between Saturn and Uranus. Therefore, it is classified as a special category of asteroids - centaurs. Nowadays, quite a few centaurs moving between the orbits of Jupiter and Neptune are known.
Other competitors became known later. Although back in 1949, the Englishman Kenneth Edgeworth and two years later the American Gerard Kuiper suggested that on the outskirts of the solar system, at a distance of 35-50 astronomical units from the Sun (remember, there is one astronomical unit from the Earth to the Sun), there is another asteroid belt . Edgeworth and Kuiper believed that it was from this belt that comets with a short orbital period come to us. However, in the indicated area, except for Pluto and its satellite, nothing could be detected.
Success came only in 1992, when asteroid 1992QB1 was discovered. By the beginning of the 21st century, 388 such celestial objects were already known. The area where they are located was called the Edgeworth-Kuiper belt (more often briefly - the Kuiper belt). The asteroids themselves are called KBOs (Kuiper belt objects) or TNOs (trans-Neptunian objects). Scientists predict that among them there may be up to one hundred thousand celestial bodies with a diameter of more than one hundred kilometers.
In the 2000s, relatively large trans-Neptunian objects began to appear. Journalists rushed to proclaim the discovery of many of them as the discovery of the tenth planet of the solar system. Guia, Quaoar and Sedna appeared under this title. Smaller objects were also discovered: Varuna, Ixion, Chaos and others. However, even the largest of them - Sedna - is inferior to Pluto in size. Among the KBOs, there were a number of those whose orbital parameters resembled the orbit of Pluto. They were given the name plutino.
New challenger
Information about trans-Neptunian objects continued to arrive. New data has been received about the celestial bodies 2003 EL61, 2005 FY9 and 2003 UB313, which received the names (still unofficial) Santa, Easterbunny and Xena. Santa even has a companion, Rudolph. Easterbunny, for example, has methane ice like Pluto. But the most interesting of the newcomers is Xena.
Not only does it have a satellite (unofficial name - Gabriella) and methane ice on the surface. Xena also turned out to be the largest of the celestial bodies located further from the Sun than Pluto. Xena was discovered by Mike Brown from the California Institute of Technology, who has already become famous for the discoveries of many trans-Neptunian objects. Brown said he estimates Xena's diameter to be between 2,210 and 3,550 km. This was already a serious claim - a body superior to Pluto could lay claim to the proud title of a planet.
However, it is worth remembering that the estimate of Xena's size is based on data on the reflection of sunlight from its surface. As we said earlier, it was this method that led to an error in determining the size of Pluto. But scientists claim that even in the worst case, Xena is no less than Pluto. Recently, the size of the new planet, 3000 km, was confirmed by research by Frank Bertoldi, an employee of the University of Bonn and the Max Planck Institute for Radio Astronomy. Bertoldi studied Xena's reflection of radio waves. Still, the most accurate method is to observe the rare moment when a planet covers a star. Then, based on the duration of the eclipse, you can accurately calculate the size of the planet. This is how they found out the diameter of Pluto at one time. It's a pity that you have to wait for such an opportunity.
As astronomers have established, Xena makes one revolution around the Sun in 557 years. Its orbit, like that of Pluto, is elongated: at perihelion it goes inside the orbit of Pluto, and at aphelion it moves away from the Sun even further than Sedna. The inclination of the orbit to the plane of rotation of the eight main planets is also large - 45 degrees. All this again may become an obstacle to Xenu being called a planet.
It should be noted that an important feature of a planet is its internal structure (presence of a core, etc.). While Pluto, Xena and other trans-Neptunian objects are quite possibly frozen blocks consisting of rock and ice. Therefore, Xena's chances of becoming the tenth planet are not that great. Most likely, Pluto, due to its fellow plutinos discovered in recent years, will cease to be considered a planet, and there will be eight planets in the solar system. However, Pluto can be saved by tradition and people’s habit of its status. Maxim RUSSO |
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