Astronomy In an ever-evolving universe, planetary definitions must sometimes catch up with new discoveries and understandings.
The term „planet” as defined International Astronomical Union (IAU)Currently under investigation.
The long-standing definition describes a planet as a celestial body orbiting the Sun that has enough mass to be forced into a spherical shape by gravity and has removed other objects from its orbit.
However, this IAU definition only applies to celestial bodies in our solar system, sparking debate among scientists.
Expanding the definition of planets
We live in a vast universe where celestial bodies orbiting outside our own solar system are frequently discovered.
This reality prompts a thought-provoking question: Shouldn’t the definition of a planet extend beyond the boundaries of our solar system?
A paper soon to be published in a well-known scientific journal argues in favor of it. The study authors propose a new definition of a planet — one unconstrained by the boundaries of our solar system and enhanced by size criteria.
An outdated definition of planets
Scientists who pioneered this project University of California, Los Angeles (UCLA). They champion an alternative to the IAU’s definition, which they consider heliocentric and outdated.
„The current definition specifically refers to orbiting our Sun. It only applies to planets in our Solar System,” said Professor Jean-Luc Margot, lead author of the study. He said the group’s proposal would apply to celestial bodies orbiting any star, stellar remnant or brown dwarf.
Researchers argue that the IAU’s requirement for a planet to orbit our Sun is too specific, while other criteria are too vague.
They present a clear definition, replete with criteria applicable to planets both inside and outside our solar system.
Properties of planets
According to the new proposal, a planet is a celestial body orbiting one or more stars, brown dwarfs or stellar remnants. Its mass is over 1,023 kg, but less than 13 Jupiter masses (2.5 X 1,028 kg). Providing such specific mass limits is an important element of the proposal.
Scientists used a mathematical method to study the properties of objects in our solar system and identify unique properties shared by our planets.
The analysis served as the foundation for creating a universal classification for these celestial bodies, introducing important elements such as kinetic dominance.
Mass and Gravitational Influence
An object is said to be dynamically dominant if it has enough gravitational force to clear a path by accreting or ejecting smaller nearby objects.
Interestingly, all planets in our solar system exhibit this characteristic, but dwarf planets like Pluto and many asteroids do not. As a result, this characteristic has been cited as an important addition to the planetary definition.
While kinetic dominance sets a lower mass limit, mass also acts as an upper limit, especially when celestial bodies are so massive that they begin thermonuclear fusion of deuterium and become companion stars known as brown dwarfs.
Notably, requiring a planet to be spherical is more complicated to implement due to the difficulty of observing the shapes of distant planets.
Therefore, the authors propose basic definitions in mass that are easy to measure, thereby avoiding debates about whether or not a celestial body meets the sphericity criterion.
Planets and dwarf planets
A revision of the official IAU definition of a planet may not be forthcoming, but the researchers hope their work will spark a debate that could lead to an improved definition.
Under the proposal, the difference between planets and dwarf planets becomes clear.
Dwarf planets like Pluto, which lack dynamical dominance, are part of a separate category. This ensures that the definition includes only bodies that fit the strict mass and kinetic dominance criteria.
Understanding extraterrestrials also plays an important role in the debate. Exoplanets—planets located outside our solar system—demand a definition that transcends the confines of the solar system.
By focusing on the influence of mass and gravity, the new definition provides a robust framework, making classification easier and more accurate.
The thesis has been published The Planetary Science Journal.
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