Nasa's 'holy grail': Solar system that could support alien life discovered

It is ‘amazing’ how similar the entire solar system is to Earth

Scientists have found a new solar system filled with planets that look like Earth and could support life, Nasa has announced.

At least three of the seven planets represent the “holy grail for planet-hunting astronomers”, because they sit within the “temperate zone” and are the right temperature to allow alien life to flourish, the researchers have said. And they are capable of having oceans, again suggesting that life could flourish on them.

No other star system has ever been found to contain so many Earth-sized and rocky planets, of the kind thought to be necessary to contain aliens.

The researchers might soon be able to find evidence of life on the planets, they have said. British astronomer Dr Chris Copperwheat, from Liverpool John Moores University, who was part of the international team, said: “The discovery of multiple rocky planets with surface temperatures which allow for liquid water make this amazing system an exciting future target in the search for life."

Any evidence of life is likely to be “strong, very strong or conclusive”, the scientists said. It will be done by looking for what molecules are in the atmosphere – if they were to find things like oxygen, and in the right amounts, then it would probably indicate that there was biological activity.

Co-researcher Dr Amaury Triaud, of the Institute of Astronomy in Cambridge, said: “We hope we will know if there's life there within the next decade.”

Even if life isn’t ever found near TRAPPIST-1, it might eventually develop there. The star is relatively young – even when our own Sun has run out of fuel and our solar system is destroyed, the newly-discovered one will still be in its early infancy.

TRAPPIST-1 “burns hydrogen so slowly that it will live for another 10 trillion years – more than 700 times longer than the Universe has existed so far, which is arguably enough time for life to evolve”, wrote Ignas AG Snellen from the Leiden Observatory, in an accompanying article about the discovery.

All of the planets were found using a method called “transit photometry”. That works by watching out for when a planet passes, or transits, in front of its host star – blocking out a small amount of light, allowing us to see the planet and learn about its size.

Scientists first found the star TRAPPIST-1 in 2010, after monitoring the smallest stars close to the Sun. Since then, they have been watching out for those transits – and after seeing 34 of them clearly, they proposed that they can be attributed to the seven new planets.

They then worked to understand the size and composition of each of the worlds. That work is still continuing, but the researchers believe that the planets have large oceans, are temperate and other conditions that could make way for alien life.

Dr Michael Gillon, from the STAR Institute at the University of Liege in Belgium, said: “This is an amazing planetary system – not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth.”

If a person were on one of the planets, everything would look a lot darker than usual, the scientists said. The amount of light heading to your eye would be about 200 times less than you get from the sun, and would be comparable to what you can see at sunset.

Despite that relative darkness, everything would still feel warm, the researchers said. That’s because roughly the same amount of energy would be coming from the star as warms our Earth – but it does so infrared.

Because the star is so dim in relative terms, all of the planets are warmed enough to sit in the temperate zone. That’s despite the fact that they are all so close to it – each of them sitting nearer to the star than Mercury, the planet in our solar system that orbits closest to the Sun.

“The spectacle would be beautiful,” said Amaury Triaud, one of the scientists involved in the research. “Every now and then you’d see another planet, about as big as another moon in the sky.”

The sun would also look about 10 times bigger than our own does from Earth, Dr Triaud said, despite the fact that it is in fact only 8 per cent as big. And it would be a sort of salmon pink, said Dr Triaud, who noted that the scientists initially thought it would be a deep reddish crimson but most of that red light would be infrared and so invisible.

This chart shows, on the top row, artist conceptions of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii and masses as compared to those of Earth. The bottom row shows data about Mercury, Venus, Earth and Mars (NASA/JPL-Caltech)

It’s unlikely that any possible life that is on the planet would actually see this way, the scientists noted, since they would probably have evolved entirely different eyes – or perhaps none at all.

The researchers hope that they can do more work to watch the planets and learn more about their character. They want to look in particular at the seventh, outermost planet because at the moment they are not sure how it interacts with the inner ones.

Nasa's Hubble Space Telescope is already being used to search for atmospheres around the planets. Future telescopes, including the the European Extremely Large Telescope and James Webb Space Telescope, may be powerful enough to detect markers of life such as oxygen in the atmospheres of exoplanets.

The first exoplanet was found in 1992. Since then, astronomers have detected more than 3,500 of the worlds, distributed across 2,675 star systems.

About a fifth of the sun-like stars are thought to have Earth-sized planets close enough to them to support life.

In all, there might be 40 billion potentially habitable words sitting just in our galaxy, the Milky Way, astronomers estimate.

Scientists have long thought that Earth-sized planets were abundant, but the new research shows just how many of them there might be. Many of those planets might never be seen, because they don’t pass in front of their host star and so aren’t visible.

That might mean that the new system is actually not all that out of the ordinary. Scientists expect that for each planet we find, there are as many as 100 we can’t see – and so the scientists might not actually have been lucky, but rather seen something that wasn’t that unusual.