Determining the mass of Pluto using its moon

In summary, the mass of Pluto was previously unknown until James Christy observed its moon, Charon, orbiting around it on June 22, 1978. By measuring the size of Charon's orbit, the gravitational force of Pluto could be calculated, which in turn allowed for the determination of Pluto's mass. However, it should be noted that the size or period of an orbit is not the only factor in determining the gravitational force, as demonstrated by the varying orbits of Jupiter's moons and Earth's satellites.
  • #1
Softshow
4
0

Homework Statement


On June 22, 1978, James Christy made the first observation of a moon orbiting Pluto. Until then, the mass of Pluto was not known, but with the discover of its moon, Charon, its mass could be calculated with some accuracy. Explain.


2. The attempt at a solution
"By knowing how large the orbit of the moon was, the mass of pluto could be calculated. In order to do this, the radius of the orbit of the moon is used because it shows the amount of gravity pluto is exerting on it. Because mass is proportional to gravity, and gravity to the size of the orbit, the mass can be calculated by looking at the size of the orbit."

I was given 4/5 credit for this with no direction as to where I went astray. I'm not sure if I was just too vague or I was simply incorrect, but any input would be greatly appreciated.
 
Physics news on Phys.org
  • #2
Unless you explain what you did, how could anyone here find out where you went wrong?
 
  • #3
Sorry I didn't explain this better, this was not given as a mathematical problem, instead it was a problem which we were expected to try and talk through. No numerical values were given, making it completely impossible to actually determine the mass of pluto. We were simply expected to demonstrate our knowledge of the concepts at work relating to this problem.
 
  • #4
I don't think the size of the orbit is the only factor. The period also has to be in there somewhere I believe.
 
  • #5
Gravity is not "proportional to the size of the orbit". Jupiter has moons with semi-major axes ranging from ~128,000 km to over 30 million km. The Earth has man-made satellites that orbit just a few hundred km above the surface (semi-major axis ~6700 km), geostationary satellites orbiting at 42,164 km, and of course the Moon at ~385,000 km.
 
  • #6
One thing I have a problem with is your references to "gravity" as if it were a specific quantity:
"amount of gravity pluto is exerting on it" and "Because mass is proportional to gravity". I presume you mean "gravitational force" but you should still tell how one could determine the gravitational force the size or period of an orbit.
 

1. How is the mass of Pluto determined using its moon?

The mass of Pluto can be determined using the relationship between the mass of a planet and the orbit of its moon. By observing the orbital parameters of Pluto's largest moon, Charon, astronomers can calculate the mass of Pluto using Newton's law of universal gravitation.

2. Why is Charon's orbit important in determining the mass of Pluto?

Charon's orbit is important because it is the largest and closest moon to Pluto. Its gravitational pull on Pluto causes both bodies to orbit around a common center of mass. By measuring Charon's orbital period and distance from Pluto, the mass of Pluto can be calculated.

3. How do scientists measure Charon's orbital period?

Scientists use telescopes to track Charon's position in the sky over time. By recording its movements and calculating the time it takes to complete one full orbit around Pluto, scientists can determine Charon's orbital period.

4. What other factors can affect the accuracy of determining Pluto's mass using Charon's orbit?

Other factors that can affect the accuracy of this method include the presence of other moons and objects in Pluto's system, as well as any variations in Charon's orbit due to gravitational interactions with these objects. Therefore, multiple observations and calculations are necessary to ensure the accuracy of the mass determination.

5. How does determining the mass of Pluto help us understand the solar system?

Determining the mass of Pluto is important for understanding the dynamics of the solar system and the formation of planets and moons. By studying the mass and orbits of objects in the solar system, we can gain insights into the formation and evolution of our own planet and others in the universe.

Similar threads

Replies
3
Views
301
  • Aerospace Engineering
Replies
6
Views
2K
Replies
17
Views
2K
  • Introductory Physics Homework Help
Replies
21
Views
2K
  • Aerospace Engineering
Replies
19
Views
2K
Replies
2
Views
984
  • Sci-Fi Writing and World Building
Replies
21
Views
851
  • Sci-Fi Writing and World Building
Replies
17
Views
2K
  • Introductory Physics Homework Help
Replies
7
Views
1K
  • Astronomy and Astrophysics
Replies
4
Views
2K
Back
Top