Chapter 11: Problem 1
The asteroid Eugenia has a small natural satellite orbiting it. The orbital period of the satellite is \(P=4.76\) days. The semimajor axis of its orbit is \(a=1180 \mathrm{~km}\). What is the mass of Eugenia? (Hint: it is safe to assume that the mass of the satellite is tiny compared to the mass of Eugenia.)
Short Answer
Step by step solution
Understand the Goal
Identify Relevant Formula
Rearrange the Formula
Convert Units
Insert Known Values
Calculate the Mass
Verify the Calculation
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Kepler's Third Law
This principle is given mathematically by:
- For a celestial body with mass, \(P^2 = \frac{4\pi^2}{G(M+m)}a^3\), where \(P\) is the orbital period, \(a\) is the semimajor axis, \(M\) is the mass of the main body, and \(m\) is the mass of the orbiting body.
- However, when \(m\) is much smaller than \(M\), as often assumed in problems like ours, it simplifies to \(P^2 = \frac{4\pi^2}{GM}a^3\).
Gravitational Constant
- \(G\) ties together the mass of the primary body (e.g., an asteroid) and the orbital characteristics of its satellite.
- It ensures units are consistent, which is essential when performing precise calculations.
Asteroid Mass Calculation
- Start by understanding the satellite's orbital period and the semimajor axis distance.
- Use the simplified form of Kepler's Third Law for systems where the satellite mass is negligible compared to the primary body: \(M = \frac{4\pi^2 a^3}{G P^2}\).
- Convert all units to International System units (meters, seconds). This ensures the calculations use consistent units for accuracy. For instance, converting the period from days to seconds and the distance from kilometers to meters is crucial.
- Substitute these values into the formula and calculate accordingly. The combination of \(G\), the period, and the semimajor axis will provide you with the mass of the asteroid.
- Ensure you verify your calculations by cross-checking the units and ensuring they result in kilograms, a standard unit of mass.