# How many earth-like planets are thought to exist in the universe?

Jan 29, 2016

Extrapolation from current estimates suggests upwards of ${10}^{20}$ Earth-like planets in the universe.

#### Explanation:

Current estimates based on data from the Kepler mission suggest that there are somewhere between 1 and 50 billion "Earth-like" planets in the Milky way alone, depending on how one defines "Earth-like".

Let's take the low end of that estimate ($1 \times {10}^{9}$ planets).

If there are more than 100 billion (${10}^{11}$) galaxies in the universe, and each is similar to the Milky Way (some are larger, some are smaller, but as an estimate it works), then each of those galaxies would also have a billion Earth-like planets.

The total number then is ${10}^{11}$ galaxies times ${10}^{9}$ planets / galaxy:

${10}^{11} \cdot {10}^{9} = {10}^{20}$

or

$100 , 000 , 000 , 000 , 000 , 000 , 000$

That's probably more than the number of grains of sand on every beach on Earth. In other words, a LOT .