Video transcript

Between the Andes mountains and the pacific ocean, on the remote southern edge of the Atacama desert lies one of the most extraordinary observatories on Earth.

The high elevation and the low rainfall, just 1mm a year, makes it the perfect place for uninterrupted views of the southern night sky.

It was here in 2007 that a Swiss team of astronomers made a discovery that transformed our place in the Universe.

UDRY: Please come in I have something to show you in here.

Prof Stephen Udry is the proud owner of a machine which could change the course of human history.

UDRY: Inside this big box is an enclosure and inside this is a vacuum tank, with the instrument that is the most sensitive in the world now for planet detection.

With this instrument we can detect low mass planet 5, 10 times the mass of the Earth.

PRODUCER (off camera): Can we go in?

UDRY: No of course not, because just opening the door will destroy the measurement for a few days. Because we need to have a very stable instrument to be able to repeat the measurement with the same precision day after day, month after month, years after years.

And that's exactly what they've been doing.

They drew up a list of a thousand targets taken from the Gliese Catalogue of Nearby Stars...

...and began measuring and re-measuring each candidate, hunting for wobbles that had previously been too small to detect.

But one star caught Stephan's attention.

UDRY: Gliese 581 was in our target list since the beginning.

Categorised as Gliese 581a. It's a red dwarf star, a third of the mass of our own sun.

When the wobble was plotted it revealed 581b, a massive planet the size of Neptune, close into the star and orbiting once every five and a half days.

It was no Earth, but the star's wobble held some fine detail that still intrigued Stephan.

UDRY: We noticed that there was something else in the system.

There seemed to another, smaller planet lurking in the detail.

UDRY: That something else could be a five earth mass planet very close to the star.

If Stephan's hunch was right, it would be the smallest planet ever detected around a distant sun.

And this planet seemed to be habitable.

UDRY: We got excited because the distance was just right for the planet to possibly be in the habitable zone.

After years of hunting, the search for the first second earth was over.

NEWS: European astronomers have spotted a new planet outside our solar system which closely resembles the planet Earth. They believe it could support water and potentially, life.

NEWS: But this latest find has set the world of astronomy alight.

For the Swiss team, the breakthrough was a triumph.

UDRY: It is always very exciting to be the first one to know.

MARCY: The discovery of gliese 581c is a marvellous discovery. It shows how close we are were getting to planets that remind us of the earth.

DRAKE: It shows that potential life baring planets do exist. This is the first one where that seems to be clearly the case.

UDRY: When you know and you realise it, it's like being in the spaceship coming to a planet and being the first one to see the landscape.

For those tempted to make the journey, pick a clear night and look for the constellation Libra.

Invisible to the naked eye, Gliese 581 lies just north of the brightest star in the constellation.

Remarkably, it's one of our closest neighbours, a shade over twenty light years distant.

At the heart of the system is the parent star. Close by is the 581b, sixteen times as massive as Earth and too hot for life to survive.

Beyond, just on the inner warm edge of the habitable zone lies Gliese 581c: The smallest and most earth-like exo-planet yet detected.

At last scientists have found another planet that may just be capable of supporting life.

ROTHSCHILD: Wow not much out here. A lot of UV radiation. Nothing green, nothing coloured I can see, very dry.

For astrobiologists like Dr Lynn Rothschild, its discovery means they can begin to imagine what it would be like to spend a day on a Super-Earth.

ROTHSCHILD: We're up here on the edge of the Atacama desert in Chile right on the edge of the Bolivian border. You can see it's very dry, in fact its one of the driest places on Earth.

This is a great place to sort of get an idea of what an extra-solar planet for example G581c might be like.

ROTHSCHILD: Lets imagine were on G581c. There's an awful lot of rocks around. It's dry.

The planet's mass is five times that of Earth. This means that gravity will pull twice as hard.

Whereas on the moon the astronauts could jump with no effort, on this planet you would be suffering from extra gravity.

If you took a rock and you threw it, it would come crashing down , much faster than that of the earth.

High gravity will affect the look of the planet. No high mountains. Just low hills and vast plains.

And the last thing is that it's close to the parent star, and so the radiation from the sun would be much stronger on the Earth. Here we are getting burned, there we would probably be fried.

The planet's red dwarf star will dominate the sky, a red fiery ball five times larger than our own sun back home.

And a few hours into their trip, interstellar visitors will discover that sun never moves.

The planet is so close to its star that immense gravitational forces have united the two.

They're tidally locked, with the planet presenting just one face to the light.

LYNNE: On the earth we're used to getting up in the morning, the sun rises. We have our midday meals, in the evening we have dinner, if we're lucky we have a nice sunset.

But on something like G581c its totally different, because its tidally locked in to its parent star. And so the sun will always be in the same position all day long.

So if I wanted to the equivalent of a sunset, I'd be the one who'd have to get into the car and move.

Beyond this point is the dark side of the planet, perpetually turned outwards to the cold of space.