We live on a pale blue dot, a tiny oasis of life in a vast and silent cosmos. But are we alone? Are there other worlds like ours, orbiting other stars, in other parts of our galaxy?
The answer is yes. There are billions of them.
Thanks to the remarkable achievements of space telescopes like Kepler and TESS, we have discovered over 5,000 exoplanets – planets beyond our solar system – and thousands more await confirmation. These exoplanets come in all shapes and sizes, from gas giants larger than Jupiter to rocky worlds smaller than Earth. Some are scorching hot, some are freezing cold, and some are just right.
How do we know which ones are just right? We look for the ones that orbit within the habitable zone of their stars – the range of distances where liquid water could exist on the surface. Liquid water is essential for life as we know it, and it is also a good indicator of a planet’s climate and geology. They are the best candidates for finding life in our galaxy.
But how many exoplanets are in the habitable zone? A recent study estimated that there could be 300 million habitable planets in the Milky Way. Some are just 30 light years from the Sun, which means that if we could travel at the speed of light, it would take us only 30 years to reach them. Of course, we can’t travel at that speed, but we can still observe them with our telescopes and learn more about their properties and potential for life.
But even 300 million is just a fraction of the total number of exoplanets in our galaxy. The study extrapolated that figure from a sample of stars observed by Kepler, which only covered only one section of the sky in the constellation of Cygnus the Swan. Astronomers estimate based on Kepler observations, that every star in the Milky Way has at least one planet, and there are roughly 400 billion stars in the galaxy, which means there are hundreds of billions of planets in our home galaxy.
That’s an astonishing number. NASA estimates that there are at least 1,500 planets within just 50 light years of Earth.
But our galaxy is not alone. There are billions of other galaxies in the observable universe, each with billions of stars and planets of their own. The number of exoplanets in the cosmos is beyond our imagination.
We may never be able to visit them all, or even detect them all, but we can still marvel at their existence and wonder about their mysteries. We can still dream of finding another pale blue dot, another oasis of life, another civilization among the stars.
We are not alone. We are part of a cosmic family, a galaxy of worlds.