Counting all the atoms in the solar system

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

13 September 2020

Three weeks ago, I showed how the number of atoms that make up the Earth can be counted. The answer was a mindbogglingly large number with 50 zeroes! I wonder what that number would be called…

In the American counting system, million has 6 zeroes, a billion 9; a trillion 12, a quadrillion 15, and so on up to a decillion which has 33 zeroes. After that there is undecillion with 36, duodecillion 39, all the way up to quindecillion which has 48 zeroes. Thus, the number of atoms that make up our planet is in the order of 100 quindecillion.

Now, a few readers challenged my calculation noting that different atoms have different masses. Indeed, one pointed out that the heaviest is about 200 times the mass of the lightest. This is true, but these elements comprise a very small portion of the Earth. So, their number does not affect the number of digits in the final count.

 The same kind of argument can be applied in estimating the number of atoms that make up the entire solar system. This region of the universe is dominated by the sun. Its mass is about 2,000,000,000,000,000,000,000,000,000,000kg. That is, 2 followed by 30zeroes; or, if you prefer, two nonillion kilograms!

The mass of largest planet, Jupiter, in kilograms is the number 2 followed by 27 zeroes. That is, the sun is 1,000 times the mass of Jupiter. Nevertheless, Jupiter is more than double the combined mass of all the other planets.

It turns out then, that the sun over three hundred times more massive that all the planets put together! Therefore, if we count the number of atoms that make up the sun, we can ignore those of the planets since they won’t change the number of digits in the answer.

Now the sun is predominantly made up of hydrogen (75 percent) and helium (25 per cent). Even though helium is four times the mass of hydrogen, it only makes up a quarter of the sum.

Therefore, one kilogram of these two elements mixed in that ratio will have about two octillion atoms (27 zeroes). So, the total number of atoms in the sun is number with 27 zeroes multiplied by another with 30 zeroes.

The answer is number with 57 zeroes; that is, an octodecillion atoms. This is ten million times the number of atoms that make the earth, but it is still much, much smaller than a googol!