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An artist's impression of a startling discovery deep in space. Around a faint and distant star much weaker than our Sun is a collection of planets that are surprisingly similar to Earth. In all, seven of these worlds have been spotted, and astronomers think it may change the way we look at the night sky.

An array of telescopes kept watch on one point in space, and what the scientists were looking for were tiny clues about the light of a particular star becoming dimmer on a regular basis as planets orbited in front of it. They can't see these new worlds, but they know they're there.

We're extremely excited. This is the biggest amount of planets that we found in one go that looked like the earth in composition, size and mass. All seven are close enough to the star and far enough to the star that they could host liquid water. And that's that's just incredible.

This is the latest revelation in a wave of discoveries over the past 25 years of new worlds that exist in solar systems beyond our own. The total of these distant planets now stands at well over 3000.

What makes this discovery so unusual is the sheer number of new world spotted in one go. Seven in all. And crucially they're just the right temperature for liquid water to exist at the surface. Three of them are in what's called the habitable zone, which raises the tantalizing possibility that they could conceivably host life.

But we won't be getting there in a hurry. They are 40 light-years away. To reach them using the rockets we have now would take something like seven hundred thousand years.

There's so much to find out about these worlds: whether the artist's impressions are right, whether it's possible that the conditions for life do exist. And astronomers say there'll be a huge effort to try to find out.

The more we look, the more planets we find, and the more earth-like planets we find. But this is especially exciting because this of an ultra-cool star that was discovered. They're quite populous throughout our galaxy. And it's a first time with sun planets going around a star like this. And we found seven of them.

The best hope lies with huge new telescopes that will come into service soon, improving the chances of getting a really close look at these alien worlds. To see for example if they do have oceans, and maybe, just maybe, discover if there are some hints about life.

David Shrukmen, BBC news