Teacher is confused about the decision that is taking shape among the members of the International Astronomical Union
Avi Blizovsky
Pluto and Charon. Pluto has gone down a bit, Charon has ascended
Hasn't there been a definition for the term planet until now?
There was no agreed formal definition. For hundreds of years, planets were simply objects that moved in the sky relative to the background of the fixed stars. The word "planet" comes from the Greek word for "wanderer". However, astronomers today know more about many types of planets orbiting suns outside the solar system. Finally, the IAU decided it was time to agree on a scientific definition for the term.
What is the definition they decided on?
In order for a celestial object to be declared a planet, it must meet two conditions:
1: The object must orbit a star, but it itself will not be a star.
2: It must contain enough self-mass so that gravity causes it to have a shape close to a sphere.
In fact, the second condition is met by any object that has 60% of the mass of the Earth's moon, and a diameter greater than 800 kilometers. But borderline irritants will have to be resolved through more observations.
Some objects that are now considered moons and asteroids can meet this condition if they answer these basic questions. So the definition leaves the door open for more objects to join the expanding club.
So has Pluto been demoted or not?
In a sense, Pluto did degrade. This world was always the odd one out. It has a mass less than 1/400 that of Earth and has a highly inclined elliptical orbit around the Sun. Therefore, in the draft proposal that is being voted on, it is written that in fact there are eight "classical" planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, three more "Plutonic objects": Pluto Charon and UB313 (temporary name Xena), and The collapsed asteroid is very close to a sphere in shape.
Many astronomers believe that Pluto is part of a large population of icy objects circling the Sun beyond Neptune in the region known as the Kuiper Belt. The origin of these objects is different from planets like Earth and Jupiter. They are also considered remnants left over from the creation of the solar system.
The sharp category of Plutons distinguishes Pluto and the other icy bodies from the classical planets in that their orbits are inclined and far from circular, and that they take over 200 years to complete one revolution around the Sun.
However, the Plutonian objects meet all the criteria that define a planet, therefore Pluto did not receive the full reduction in degree that some of the astronomers had hoped for.
Is the moon also entitled to be considered a planet?
No. The moon is a satellite of the earth. The center of gravity of the system lies below the surface of the Earth.
So what do we know about the "new" planets?
Ceres is the largest object orbiting the Sun in the asteroid belt between Mars and Jupiter. It was declared a planet when it was discovered in 1801, but because the astronomers of the 19th century could not estimate the size and shape of the object and because numerous objects orbiting the sun were discovered in the same area, Ceres lost its planetary status. For over a century, it was considered an asteroid or a minor planet. Ceres now fits the definition because it has a large enough mass and a strong enough self-gravity to make it nearly spherical.
Charon was discovered in 1978 by James Christie, an astronomer at the US Naval Observatory in Washington, DC. Until now, it was considered a moon of Pluto. Both of these bodies, Pluto and Charon, have enough mass to take on a spherical shape - both individually meet the definition of a planet.
Pluto and Charon are now considered more like "planet twins" because the common center of gravity of the system is in outer space outside the surface of Pluto.
2003 UB313 was discovered by American astronomer Mike Brown and his colleagues at Caltech three years ago. This year, measurements made by the Hubble Space Telescope revealed that it is larger than Pluto. Like Pluto, it is an icy body that orbits the Sun beyond Neptune in the Kuiper Belt. It is about 16 billion km from the Sun - 3 times as far as Pluto, and it takes more than twice the time to orbit the Sun. The name is provisional and the IAU must agree on an official name. Brown's group names the object Xena, after the warrior princess from the television series bearing her name, and the moon Gabrielle, after one of the series' supporting characters.
As a result of the decision, may the number of planets increase?
Yes, almost certainly. Since the beginning of the nineties of the 20th century, astronomers have discovered many new objects orbiting the Sun beyond Neptune - something made possible thanks to advanced technology. The IAU has a "watch list" of about a dozen potential candidates that could become planets once their size and orbit are known for sure. Among these bodies is Sedna, which was the first object discovered in the hypothetical region at the edge of the solar system known as the Oort cloud, as well as several objects in the Vakiper belt that approach Pluto in size. Three asteroids are also on the watch list: Vesta, Pallas and Hygieia.
Astronomers recently discovered two new satellites orbiting Pluto. Does this make Pluto a square planet?
No. The two newly discovered moons are too small and not massive enough for gravity to make them spherical in shape. These are satellites, although their center of gravity is outside the surface of Pluto.
The list of candidates to be considered as planets
Trans-Neptunian objects:
● 2003 EL61
● 2005 FY9
● Workshop
● Orcus
● Quahwar
● Varona
● 2002 TX300
● Ixion
● 2002 AW197
Asteroids:
● Vesta
● Pallas
● Pronunciation
