Astronomers want to change the definition of a planet
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Is Pluto a planet? You may have noticed that it has entered and exited that definition for years. In case you’re wondering, it’s not a planet anymore; it’s a dwarf planet.
Scientists change these definitions as they discover more about the world. Specifically, astronomers continue to learn more about outer space, challenging previous knowledge.
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That is why UCLA professor Dr. Jean-Luc Margot and his team submitted a new definition for the heavenly body to The Planetary Science Journal.
What truly is a “planet?”
ICYMI: The @IAU_org defines a planet as a celestial body that orbits our sun. ☀️🌍🪐 But scientists including UCLA astronomer @JeanLucMargot are proposing a new definition—and hope to get the astronomical conversation flowing. https://t.co/x9xNde1Wg3 #Astronomy #PlanetaryScience
— UCLA College (@UCLACollege) July 29, 2024
Educational website New Atlas reported that the International Astronomical Union (IAU) first established the definition of a planet in 2006. This set of criteria is called the IAU Resolution B5, and it has the following rules:
Article continues after this advertisement- The planet must orbit around the Sun.
- Also, it must have enough mass to become roughly round.
- It should clear the neighborhood around its orbit.
B5 already had skeptics at the time due to its vague definitions. For example, the first assumes that planets only exist in our solar system.
However, astronomers have discovered over 5,000 around other stars. Moreover, Philip Metzger, a planetary scientist who worked on the New Horizons mission’s Pluto probe, said he has an issue with the third definition.
“They didn’t say what they meant by clearing their orbit. If you take that literally, then there are no planets because no planet clears its orbit,” he stated.
“The most problematic by far is the roundness criterion,” stated Dr. Jean-Luc Margot.
“Roundness is simply not observable. We do not have the technology, and we will not have the technology anytime soon,” the lead researcher added.
That is why Dr. Margot and his team thought people should define these heavenly bodies based on easily measurable properties: orbital elements and masses.
They computed the differences between a planet and a satellite to provide the new definition:
- A planet orbits one or more stars, brown dwarfs, or stellar remnants;
- It is more massive than 1023 kg; and
- Moreover, it is less massive than 13 Jupiter masses (2.5 x 1028 kg)
“Having definitions anchored to the most easily measurable quantity – mass – removes arguments about whether or not a specific object meets the criterion,” said Brett Gladman, co-author of the study.
