Whether the Moon (Earth's natural satellite) is a planet is an old debate in planetary science.
Though I do not agree that Moon is a planet, I found something difficult to clearly understand.
According to the 2006 IAU definition of planet, a planet must satisfy Clearing the neighbourhood condition. And some criteria for the condition are introduced in the Wikipedia article about Clearing the neighbourhood.
- Stern–Levison's $\Lambda$
$$\Lambda = \frac {m^2}{a^{\frac 3 2}} k$$
- Margot's $\Pi$
$$\Pi=\frac {m}{m^{\frac 5 2}a^{\frac 9 8}} k $$
In the above equations, $m$ is the mass of the body, $a$ is the body's semi-major axis, and other factors are described in the Wikipedia article. Both criteria are said to be satisfied if the calculated value is greater than 1.
My calculations are simple. Let $m_{Moon} = 0.0123 \times m_{Earth}$ and Moon's other factors (such as $a$, $k$ and $M$) have the same values as Earth's. Then I can get...
$$\Lambda_{Moon} = 0.0123^2 \times \Lambda_{Earth} = 23.147$$
$$\Pi_{Moon} = 0.0123 \times \Pi_{Earth} = 9.963$$
Both $\Lambda_{Moon}$ and $\Pi_{Moon}$ thus satisfy the Clearing the neighbourhood condition. Though I do not calculate the Soter's $\mu$, it will not change my results.
What is wrong with my calculations and results? Do I miss something about the condition and the criteria? Or is there something wrong with the Clearing the neighbourhood condition?
Edit in response to comments:
This question can be related to the idea that the Clearing the neighborhood condition is inadequate and ambiguous for the planet definition.
More deeply, this question can be related to the idea that 2006 IAU definition of planet is logically ambiguous and clumsy.
For example, the 2006 definition of planet defines the Moon as a satellite and not a planet.
If one celestial body can be defined as a planet or not without rules and conditions, why other conditions are needed? All we need is just a planet list, not other planet conditions.
And...
Frankly speaking, the Clearing the neighborhood condition is like comedy. The condition says "Planet must sweep out other bodies" ... Then says "Except satellites" ... Then again says "Except bodies having no significant size" ... Then again "Except bodies having resonant orbit" ... Then again "It may take billions of years" ... Then again "Sweep-out process and time are influenced by other planets and bodies, actually" .......
It is obvious that sometimes the Clearing the neighborhood theory is useful. But it is inappropriate for the rule and definition requiring strictness.
Edit
section has some problems. But the original purpose of theEdit
section is to prevent repeated comments and queries. As you can see, this question has been involved with more complex and broader issues than I expected. So I hesitate to delete the section. $\endgroup$ – pdh0710 Nov 25 '18 at 3:42