Have you ever looked up at the night sky and wondered whether, somewhere out there in the blackness of space, a planet not unlike Earth revolves around a foreign sun?

Scientists now know that the answer is a resounding yes - and on Wednesday NASA made an astonishing announcement: it had found not one, but seven potentially Earth-like planets at once.

They are all orbiting a small, faint star called Trappist-1, around 39 light-years away. Each planet is a similar size to Earth, and they are close enough to the cool sun to be the perfect temperature for liquid water - and maybe even life.

"This is really something new," said the astrophysicist Ignas Snellen.

The findings confirm the idea that Earth-like planets are extremely common. In fact, back in 2013, NASA predicted that there could be at least 17 billion Earth-like planets in the Milky Way alone - possibly as many as 50 billion.

The vast majority of those are not inhabited, of course - or even habitable. Only some will be in the "Goldilocks zone" of a star's orbit, while many will have unfriendly atmospheres thick with hydrogen and helium. And it is unclear how many of the planets might harbour the water molecules which are so vital to life as we understand it. So none of this is proof of alien life - though those who dream of other worlds will be hugely excited by the news.

Nevertheless, this latest discovery is momentous in itself. Scientists are now focusing on discovering whether any of the new planets have atmospheres. The James Webb Telescope, which will replace the Hubble telescope next year, will give a much clearer picture of the distant solar system.

The idea that these planets are just seven of a potential 50 billion - in our galaxy alone - is staggering. When Earth was first photographed from outer space in images liken Earthrise and The Blue Marble, its fragile, isolated beauty changed the way people thought about our planet. It was, said one photographer, "the beginning of the environmental movement".

To some, the vast array of other planets makes life here on Earth seem totally insignificant. When we are just a speck on the edge of infinity, they ask, why worry about bills or deadlines or social expectations? Discoveries like these teach us that we might as well do as we please - the universe does not care.

For others, the vastness and dignity of space sparks exactly the opposite revelation: being part of something so unfathomably enormous is humbling. The fact that our lives are played out on the corner of such an awesome stage gives our actions greater significance, they say, not less.