The Pfeifer Equation

What About Moons

In addition to exoplanets, astronomers have also pointed to moons as candidates for extraterrestrial life. In total, there are 288 known moons that orbit the 8 planets in our solar system. Jupiter's Europa and Ganymede, along with Saturn's Titan, among others, are renowned for their potential to house subsurface oceans. These icy worlds experience surface temperatures below -200 degrees Fahrenheit. Despite this, many are hopeful that something could be living below the thick outer layers of ice. Titan, specifically, has evidence of liquid methane lakes on its surface. Some have theorized that this feature could lead to "life" with building blocks made of methane or other chemicals dissimilar to ours. Although this is an interesting idea, there is no evidence that such a phenomenon is possible. It also begs the question of whether something with different building blocks, fulfills the criteria to be considered "alive."

You may have noticed that moons do not play a role in any of the factors in the Pfeifer Equation. This is because moons likely do not satisfy the factors in the Pfeifer Equation at the same rates as planets. If moons were to be added as a factor in the number of worlds section (purple factors), we would be under the assumption that moons experience the orange and red factors at the same rates as planets do. Pfeifer was not comfortable making this assumption. Additionally, we have yet to confirm the finding of any moons orbiting exoplanets ("exomoons"). Discovering exoplanets is already hard enough, so one can imagine the difficulties in finding exomoons. Furthermore, gauging how common moons are in other solar systems is equally challenging. For all we know, our solar system could have a well above or well below average amount of moons (per planet). Without observing exomoons, there is no way to know.

When making your own equation, you could consider adding a "Moons Per Planet" factor if you are comfortable making the assumption that was mentioned earlier. If you do wish to add this factor to the number of worlds section, be aware that multiplying a number of planets by moons per planet will give you a number of moons. To avoid this issue, you can add 1 to your estimate of moons per planet. By doing this, your number of worlds section will result in a number representing the estimated number of planets and moons combined in the galaxy. For context, the observed average number of moons per planet in our solar system is 288/8 = 36.

Your number of worlds section may look something like this:

Number of Worlds (Alternate Calculation)

Number of Stars in the Galaxy
x
Planets Per Star
x
(
1
+
Moons Per Planet
)

Another solution to this issue is to call your factor "Moons Per Star." With this approach you would separately multiply the number of stars by planets per star and by moons per star. This results in a number of planets in the galaxy and a number of moons in the galaxy, which you can add together. This method will come out to a different estimate than the one above since most other solar systems do not have as many planets as ours.

Your number of worlds section could also look something like this:

Number of Worlds (Alternate Calculation)

(
Number of Stars in the Galaxy
x
Planets Per Star
)
+
(
Number of Stars in the Galaxy
x
Moons Per
Star
)
The Drake Equation
The Math Factors Estimates How Long Until We Find Aliens What About Moons Make Your Own
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Made by Nicholas Pfeifer