For many, the definition of a planet became clear when Pluto was downgraded from a planet to a dwarf planet in 2006. Now, a team of astronomers is calling for a redefinition of “planet” itself to include objects that orbit stars other than the Sun.
Team paper The paper, currently available on the preprint server arXiv, will be published ahead of next month’s International Astronomical Union general assembly, which established the current planet definition in 2006, when Pluto did not meet the criteria.
Why are we still talking about Pluto?
To be clear, Pluto is not the focus of the team’s petition. Rather, the team’s focus is on the thousands of exoplanets orbiting stars outside our solar system that are excluded from the current definition of a planet.
NASA has confirmed about 6,000 exoplanets in the observable universe, but the agency estimates there are billions more. Exoplanets are fascinating grounds for all kinds of research. Questions about planetary evolution, Growth of the star systemand Even astrobiology—The search for extraterrestrial life.
“All planets in the solar system are dynamically dominated, but other objects, including dwarf planets like Pluto and asteroids, are not,” Jean-Luc Margot, a planetary scientist at the University of California, Los Angeles (UCLA) and lead author of the study, said at the university’s release. release“So this property can be included in the definition of a planet.”
How does the proposed definition of “planet” differ from existing definitions?
In 2006, the IAU famously removed Pluto from its list of planets, because it did not meet the Union’s criteria, which state on their website that it is the solar system’s largest planet:
- Orbits a star just like Earth and Jupiter orbit the Sun
- Large enough to be almost circular
- It must have a significant effect on the orbital stability of other nearby objects.
The definition by the newer team is broader and doesn’t apply specifically to objects in our solar system, which is a pretty tiny slice of our galaxy’s backyard, let alone the universe. Their definition of a planet is:
- Orbit one or more stars, brown dwarfs, or stellar remnants
- is (2.2*10twenty three) pounds (10twenty threekg) and
- Its mass is less than 13 times that of Jupiter
If a planet that should be a planet is too large, like a gas giant, it will fuse with other matter and turn into a brown dwarf instead of a planet, so the team set a mass limit for the planet definition. weight Approx. 2.89*10twenty two (1.31*10twenty two The team noted that rogue planets, which float through space unbound by the gravity of a star or similar body, should meet the second criterion they outlined.
Related article: Astronomers discover more than 170 exoplanets, the largest number ever discovered
“Fixing the definition to mass, the quantity that is most easily measured, eliminates debate about whether a particular object meets the criteria,” Brett Gladman, a planetary scientist at the University of British Columbia and co-author of the paper, said in the release. “This is the weakness of the current definition.”
The definition of a planet isn’t changing anytime soon
The team plans to present their revised definition of a planet at a conference next month, so don’t expect the change to happen overnight, but if they’re successful, thousands of worlds that we call exoplanets may soon be called simply planets.
In a way, this move moves us away from isolationist categorizations of our existence: a planet doesn’t just refer to a space neighbor, but to any of the countless worlds out there.
