homework and exercises - How many atoms are there in our solar system?

Including all objects gravitationally bound to the Sun, how many atoms are there in our solar system?

Answer

Giving that most of the solar system's mass is concentrated in the sun, you may say that the order of magnitude of the number of atoms in the sun and in the solar system is the same. Thus, we may find this number by using the sun's mass and dividing it by the hydrogen's mass, because the sun is composed of it almost entirely: $$\frac{M_s}{M_h}=\frac{2\cdot10^{30}}{1.67\cdot10^{-27}}=1.2\cdot10^{57}$$

So the order of magnitude of the number of atoms in the solar system is $10^{57}$.