Exactly what a planet is has remained unclear for centuries. Objects currently called planets, moons, and even asteroids were named under the same umbrella at different times. In 2006, the organization that officially names objects in space International Astronomical Union (IAU) He eventually created a definition, and according to this definition, Pluto was removed from its planet status.
For an object to meet the IAU’s official definition of a planet, it had to meet three criteria:
- It must be in orbit around the Sun (this excludes all satellites)
- It must have enough mass to become roughly round (Asteroids are excluded)
- It must have cleared the area around its orbit (which excludes Pluto and other planet-like objects in the Kuiper belt).
However, there were those who were against this definition from the very beginning. Especially the third item is considered by scientists “uncertain” It was called.
Philip Metzger, a planetary scientist on the New Horizons mission that sent a space probe past Pluto in 2015, said: “They didn’t say what they meant by clearing their orbit. “If you take this literally, then there are no planets, because no planet clears its orbit.”
Scientists propose a new definition
Another problem is The current definition is Solar System centered. and that a planet must revolve around the Sun. But in recent years astronomers have discovered objects orbiting other stars. They discovered more than 5,000 planets. Therefore, a team of scientists proposes a new definition that not only takes this into account but also simplifies the criteria. According to the proposed new definition, a planet is a celestial body that:
- It orbits one or more stars, brown dwarfs, or stellar remnants.
- 1023 It has a mass greater than kg.
- 13 Jupiter masses (2.5 x 1028 kg) has less mass.
This new definition It expands, clarifies and simplifies the existing definition. It includes not only our own Solar System and similar systems, but also planets orbiting multiple stars and stellar remnants such as brown dwarfs, white dwarfs, and neutron stars.
Team, 1023 kg lower limit, the point at which gravity bends the object into a spherical shape He says it was determined because it happened. We usually can’t see the exact shape of a distant exoplanet, but we can measure its mass.
Will Pluto become a planet again?
However, those expecting Pluto to become a planet again will be disappointed. Because Pluto’s mass remains slightly below the limit. Therefore, Pluto dwarf planet will continue to remain so.
Another advantage of this lower bound is that it is easier to reach the target that the original “cleared orbital” matter was trying to achieve. put a direct number. Beyond this minimum mass, an object becomes “dynamically dominant” and either collects or pushes out smaller objects around it.
Jean-Luc Margot, lead author of the study, says: “All planets in our solar system are dynamically dominant, but other objects, including dwarf planets such as Pluto and asteroids, are not dominant. Therefore, this feature can be included in the definition of planet.”
Finally, the new definition puts an upper limit on how large a planet can be. Some planets are so large that their gravity triggers thermonuclear fusion of deuterium in their cores, making them making it an intermediate species between planets and stars. This is generally thought to begin with objects with masses greater than 13 Jupiters.
The researchers plan to formally propose the new definition at the IAU General Assembly in August.
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