How many planets are in our galaxy? The line begins at 100 billion

According to a new scientific estimate there are at least 100 billion planets in our galaxy, or one for every star.

Using a technique called microlensing, which can reveal the mass of planets around distant stars, an international team of astronomers have employed a statistical method to conclude that planets are indeed very common in the galaxy. Their estimate suggests that there should be about 1,500 planets within 50 light years of Earth, alone.

Their work, published in Nature today (see paper), finds there are also more Earth-sized worlds than Jupiter sized worlds in the galaxy.

Cartoon view of how common planets are in the galaxy. (ESO/M. Kornmesser)

The study uses a different technique for finding planets than the Kepler mission, which has already found several hundred confirmed planets around other stars, and has many, many more candidates.

Both teams of scientists using different methods are coming to the same conclusion that there are lots of planets out there, and lots of them are likely to be similar to Earth in size and perhaps the composition of their atmospheres. This independent confirmation is an important tool of science.

The number 100 billion is almost too big to grasp. It’s equivalent to, say, the number of neurons in your brain, or equal to approximately the number of humans who have lived since the origin of the homo sapiens species.

And who knows what species live in the great beyond?

Eric Berger

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