AkaSci 🛰️
@AkaSci@fosstodon.org  ·  activity timestamp 2 weeks ago

New definition for planet proposed by Prof. Jean-Luc Margot at the IAU in Aug 2024:
A planet is a celestial body that
1. orbits one or more stars, brown dwarfs or stellar remnants and
2. is more massive than 10^23 kg and
3. is less massive than 13 Jupiter masses (2.5 X 10^28 kg).

The new definition applies to exoplanets as well.

But, Pluto at 1.31 x 10^22 kg, will still fail to gain planetary status.

Next IAU GA - 2027, Rome.

https://newsroom.ucla.edu/releases/proposal-to-change-scientific-definition-of-planet
https://iopscience.iop.org/article/10.3847/PSJ/ad55f3
#Pluto
3/n
AkaSci 🛰️
@AkaSci@fosstodon.org replied  ·  activity timestamp 2 weeks ago

Here is a more precise but more complex proposal in the paper for the definition of a planet.

Unfortunately, the IAU in the 2024 meeting did not post the proposal ahead of time and asked the authors to present it to have a large discussion and consensus before doing anything else.

The authors state that meaningful action on the proposal does not appear likely until the next IAU General Assembly in 2027 in Rome at the earliest.

https://iopscience.iop.org/article/10.3847/PSJ/ad55f3
#Pluto
3/n

Snippet from paper about the more precise definition of a planet - A planet is a celestial body that (a) orbits one or more stars, brown dwarfs, or stellar remnants, and (b) has sufficient mass to dynamically dominate the neighborhood around its orbit, i.e., m > 0.0012 (mcentral)^(5/8) a^(9/8), where m is the mass of the planetary body expressed in Earth masses, mcentral is the mass of the central body expressed is solar masses, and a is the semimajor axis expressed in astronomical units, and (c) has sufficient mass for its self-gravity to overcome rigid body forces so that it is approximately in hydrostatic equilibrium and assumes a nearly triaxial shape, i.e., m > 10^21 kg, and (d) has a true mass below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity), and (e) has a mass ratio with the central object below the L4/L5 instability, i.e., m/mcentral < 2/(25 + √621) ≃ 1/25. A satellite is a celestial body that orbits a planet.
Snippet from paper about the more precise definition of a planet - A planet is a celestial body that (a) orbits one or more stars, brown dwarfs, or stellar remnants, and (b) has sufficient mass to dynamically dominate the neighborhood around its orbit, i.e., m > 0.0012 (mcentral)^(5/8) a^(9/8), where m is the mass of the planetary body expressed in Earth masses, mcentral is the mass of the central body expressed is solar masses, and a is the semimajor axis expressed in astronomical units, and (c) has sufficient mass for its self-gravity to overcome rigid body forces so that it is approximately in hydrostatic equilibrium and assumes a nearly triaxial shape, i.e., m > 10^21 kg, and (d) has a true mass below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity), and (e) has a mass ratio with the central object below the L4/L5 instability, i.e., m/mcentral < 2/(25 + √621) ≃ 1/25. A satellite is a celestial body that orbits a planet.
Snippet from paper about the more precise definition of a planet - A planet is a celestial body that (a) orbits one or more stars, brown dwarfs, or stellar remnants, and (b) has sufficient mass to dynamically dominate the neighborhood around its orbit, i.e., m > 0.0012 (mcentral)^(5/8) a^(9/8), where m is the mass of the planetary body expressed in Earth masses, mcentral is the mass of the central body expressed is solar masses, and a is the semimajor axis expressed in astronomical units, and (c) has sufficient mass for its self-gravity to overcome rigid body forces so that it is approximately in hydrostatic equilibrium and assumes a nearly triaxial shape, i.e., m > 10^21 kg, and (d) has a true mass below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity), and (e) has a mass ratio with the central object below the L4/L5 instability, i.e., m/mcentral < 2/(25 + √621) ≃ 1/25. A satellite is a celestial body that orbits a planet.