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.

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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."

Shape Created with Sketch. Nasa's most stunning pictures of space Show all 30 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. Nasa's most stunning pictures of space 1/30 Earth from the ISS From the International Space Station, Expedition 42 Flight Engineer Terry W. Virts took this photograph of the Gulf of Mexico and U.S. Gulf Coast at sunset Nasa 2/30 Frosty slopes of Mars This image of an area on the surface of Mars, approximately 1.5 by 3 kilometers in size, shows frosted gullies on a south-facing slope within a crater. The image was taken by Nasa's HiRISE camera, which is mounted on its Mars Reconaissance Orbiter Nasa 3/30 Orion Capsule splashes down The Orion capsule jetted off into space before heading back a few hours later — having proved that it can be used, one day, to carry humans to Mars Nasa 4/30 The Soyuz TMA-15M rocket launch The Soyuz TMA-15M rocket launches from the Baikonur Cosmodrome in Kazakhstan on Monday, Nov. 24, 2014, carrying three new astronauts to the International Space Station. It also took caviar, ready for the satellite's inhabitants to celebrate the holidays Nasa 5/30 Yellowstone from space NASA astronaut Reid Wiseman shared this image of Yellowstone via his twitter account Nasa 6/30 Black Hole Friday Nasa celebrated Black Friday by looking into space instead — sharing pictures of black holes Nasa 7/30 NuSTAR X-rays stream off the sun in this image showing observations from by NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, overlaid on a picture taken by NASA's Solar Dynamics Observatory (SDO) Nasa 8/30 Saturn This near-infrared color image shows a specular reflection, or sunglint, off of a hydrocarbon lake named Kivu Lacus on Saturn's moon Titan Nasa 9/30 Worlds Apart Although Mimas and Pandora, shown here, both orbit Saturn, they are very different moons. Pandora, "small" by moon standards (50 miles or 81 kilometers across) is elongated and irregular in shape. Mimas (246 miles or 396 kilometers across), a "medium-sized" moon, formed into a sphere due to self-gravity imposed by its higher mass Nasa 10/30 Solar Flare An X1.6 class solar flare flashes in the middle of the sun in this image taken 10 September, captured by NASA's Solar Dynamics Observatory Nasa 11/30 Solar Flare An image from Nasa's Solar Dynamics Observatory (SDO) shows a 200,000 mile long solar filament ripping through the Sun's corona in September 2013 Nasa 12/30 Cassiopeia A c A false colour image of Cassiopeia A comprised with data from the Spitzer and Hubble Space Telescopes and the Chandra X-Ray observatory Nasa 13/30 Large Magellanic Cloud galaxy An image of the Large Magellanic Cloud galaxy seen in infrared light by the Herschel Space Observatory. Regions of space such as this are where new stars are born from a mixture of elements and cosmic dust Nasa 14/30 Mars Rover Spirit Nasa's Mars Rover Spirit took the first picture from Spirit since problems with communications began a week earlier. The image shows the robotic arm extended to the rock called Adirondack Nasa 15/30 Morning Aurora From the Space Station Nasa astronaut Scott Kelly captured this photograph of the green lights of the aurora from the International Space Station 16/30 Launch of History - Making STS-41G Mission in 1984 The Space Shuttle Challenger launches from Florida at dawn. On this mission, Kathryn Sullivan became the first U.S. woman to perform a spacewalk and Marc Garneau became the first Canadian in space. The crew of seven was the largest to fly on a spacecraft at that time, and STS-41G was the first flight to include two female astronauts 17/30 A Fresh Perspective on an Extraordinary Cluster of Galaxies Galaxy clusters are often described by superlatives. After all, they are huge conglomerations of galaxies, hot gas, and dark matter and represent the largest structures in the Universe held together by gravity 18/30 Veil Nebula Supernova Remnant Nasa's Hubble Space Telescope has unveiled in stunning detail a small section of the Veil Nebula - expanding remains of a massive star that exploded about 8,000 years ago 19/30 Hubble Sees a Galactic Sunflower The arrangement of the spiral arms in the galaxy Messier 63, seen here in an image from the Nasa Hubble Space Telescope, recall the pattern at the center of a sunflower 20/30 A Hubble Cosmic Couple The spectacular cosmic pairing of the star Hen 2-427 — more commonly known as WR 124 — and the nebula M1-67 which surrounds it 21/30 Pluto image Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with colour data from the Ralph instrument to create this enhanced colour global view of Pluto 22/30 Fresh Crater Near Sirenum Fossae Region of Mars The HiRISE camera aboard Nasa's Mars Reconnaissance Orbiter acquired this closeup image of a "fresh" (on a geological scale, though quite old on a human scale) impact crater in the Sirenum Fossae region of Mars. This impact crater appears relatively recent as it has a sharp rim and well-preserved ejecta 23/30 Earth Observations From Gemini IV in 1965 This photograph of the Florida Straits and Grand Bahama Bank was taken during the Gemini IV mission during orbit no. 19 in 1965. The Gemini IV crew conducted scientific experiments, including photography of Earth's weather and terrain, for the remainder of their four-day mission following Ed White's historic spacewalk on June 3 24/30 Nasa Celebrates 50 Years of Spacewalking For 50 years, NASA has been "suiting up" for spacewalking. In this 1984 photograph of the first untethered spacewalk, NASA astronaut Bruce McCandless is in the midst of the first "field" tryout of a nitrogen-propelled backpack device called the Manned Maneuvering Unit (MMU) 25/30 Hubble Peers into the Most Crowded Place in the Milky Way This Nasa Hubble Space Telescope image presents the Arches Cluster, the densest known star cluster in the Milky Way 26/30 An Astronaut's View from Space Nasa astronaut Reid Wiseman tweeted this photo from the International Space Station on 2 September 2014 27/30 Giant Landform on Mars On Mars, we can observe four classes of sandy landforms formed by the wind, or aeolian bedforms: ripples, transverse aeolian ridges, dunes, and what are called “draa” 28/30 Expedition 39 Landing A sokol suit helmet can be seen against the window of the Soyuz TMA-11M capsule shortly after the spacecraft landed with Expedition 39 Commander Koichi Wakata of the Japan Aerospace Exploration Agency (JAXA), Soyuz Commander Mikhail Tyurin of Roscosmos, and Flight Engineer Rick Mastracchio of NASA near the town of Zhezkazgan, Kazakhstan 29/30 Jupiter's Great Red Spot Viewed by Voyager I 30/30 Chandra Observatory Sees a Heart in the Darkness 1/30 Earth from the ISS From the International Space Station, Expedition 42 Flight Engineer Terry W. Virts took this photograph of the Gulf of Mexico and U.S. Gulf Coast at sunset Nasa 2/30 Frosty slopes of Mars This image of an area on the surface of Mars, approximately 1.5 by 3 kilometers in size, shows frosted gullies on a south-facing slope within a crater. The image was taken by Nasa's HiRISE camera, which is mounted on its Mars Reconaissance Orbiter Nasa 3/30 Orion Capsule splashes down The Orion capsule jetted off into space before heading back a few hours later — having proved that it can be used, one day, to carry humans to Mars Nasa 4/30 The Soyuz TMA-15M rocket launch The Soyuz TMA-15M rocket launches from the Baikonur Cosmodrome in Kazakhstan on Monday, Nov. 24, 2014, carrying three new astronauts to the International Space Station. It also took caviar, ready for the satellite's inhabitants to celebrate the holidays Nasa 5/30 Yellowstone from space NASA astronaut Reid Wiseman shared this image of Yellowstone via his twitter account Nasa 6/30 Black Hole Friday Nasa celebrated Black Friday by looking into space instead — sharing pictures of black holes Nasa 7/30 NuSTAR X-rays stream off the sun in this image showing observations from by NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, overlaid on a picture taken by NASA's Solar Dynamics Observatory (SDO) Nasa 8/30 Saturn This near-infrared color image shows a specular reflection, or sunglint, off of a hydrocarbon lake named Kivu Lacus on Saturn's moon Titan Nasa 9/30 Worlds Apart Although Mimas and Pandora, shown here, both orbit Saturn, they are very different moons. Pandora, "small" by moon standards (50 miles or 81 kilometers across) is elongated and irregular in shape. Mimas (246 miles or 396 kilometers across), a "medium-sized" moon, formed into a sphere due to self-gravity imposed by its higher mass Nasa 10/30 Solar Flare An X1.6 class solar flare flashes in the middle of the sun in this image taken 10 September, captured by NASA's Solar Dynamics Observatory Nasa 11/30 Solar Flare An image from Nasa's Solar Dynamics Observatory (SDO) shows a 200,000 mile long solar filament ripping through the Sun's corona in September 2013 Nasa 12/30 Cassiopeia A c A false colour image of Cassiopeia A comprised with data from the Spitzer and Hubble Space Telescopes and the Chandra X-Ray observatory Nasa 13/30 Large Magellanic Cloud galaxy An image of the Large Magellanic Cloud galaxy seen in infrared light by the Herschel Space Observatory. Regions of space such as this are where new stars are born from a mixture of elements and cosmic dust Nasa 14/30 Mars Rover Spirit Nasa's Mars Rover Spirit took the first picture from Spirit since problems with communications began a week earlier. The image shows the robotic arm extended to the rock called Adirondack Nasa 15/30 Morning Aurora From the Space Station Nasa astronaut Scott Kelly captured this photograph of the green lights of the aurora from the International Space Station 16/30 Launch of History - Making STS-41G Mission in 1984 The Space Shuttle Challenger launches from Florida at dawn. On this mission, Kathryn Sullivan became the first U.S. woman to perform a spacewalk and Marc Garneau became the first Canadian in space. The crew of seven was the largest to fly on a spacecraft at that time, and STS-41G was the first flight to include two female astronauts 17/30 A Fresh Perspective on an Extraordinary Cluster of Galaxies Galaxy clusters are often described by superlatives. After all, they are huge conglomerations of galaxies, hot gas, and dark matter and represent the largest structures in the Universe held together by gravity 18/30 Veil Nebula Supernova Remnant Nasa's Hubble Space Telescope has unveiled in stunning detail a small section of the Veil Nebula - expanding remains of a massive star that exploded about 8,000 years ago 19/30 Hubble Sees a Galactic Sunflower The arrangement of the spiral arms in the galaxy Messier 63, seen here in an image from the Nasa Hubble Space Telescope, recall the pattern at the center of a sunflower 20/30 A Hubble Cosmic Couple The spectacular cosmic pairing of the star Hen 2-427 — more commonly known as WR 124 — and the nebula M1-67 which surrounds it 21/30 Pluto image Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with colour data from the Ralph instrument to create this enhanced colour global view of Pluto 22/30 Fresh Crater Near Sirenum Fossae Region of Mars The HiRISE camera aboard Nasa's Mars Reconnaissance Orbiter acquired this closeup image of a "fresh" (on a geological scale, though quite old on a human scale) impact crater in the Sirenum Fossae region of Mars. This impact crater appears relatively recent as it has a sharp rim and well-preserved ejecta 23/30 Earth Observations From Gemini IV in 1965 This photograph of the Florida Straits and Grand Bahama Bank was taken during the Gemini IV mission during orbit no. 19 in 1965. The Gemini IV crew conducted scientific experiments, including photography of Earth's weather and terrain, for the remainder of their four-day mission following Ed White's historic spacewalk on June 3 24/30 Nasa Celebrates 50 Years of Spacewalking For 50 years, NASA has been "suiting up" for spacewalking. In this 1984 photograph of the first untethered spacewalk, NASA astronaut Bruce McCandless is in the midst of the first "field" tryout of a nitrogen-propelled backpack device called the Manned Maneuvering Unit (MMU) 25/30 Hubble Peers into the Most Crowded Place in the Milky Way This Nasa Hubble Space Telescope image presents the Arches Cluster, the densest known star cluster in the Milky Way 26/30 An Astronaut's View from Space Nasa astronaut Reid Wiseman tweeted this photo from the International Space Station on 2 September 2014 27/30 Giant Landform on Mars On Mars, we can observe four classes of sandy landforms formed by the wind, or aeolian bedforms: ripples, transverse aeolian ridges, dunes, and what are called “draa” 28/30 Expedition 39 Landing A sokol suit helmet can be seen against the window of the Soyuz TMA-11M capsule shortly after the spacecraft landed with Expedition 39 Commander Koichi Wakata of the Japan Aerospace Exploration Agency (JAXA), Soyuz Commander Mikhail Tyurin of Roscosmos, and Flight Engineer Rick Mastracchio of NASA near the town of Zhezkazgan, Kazakhstan 29/30 Jupiter's Great Red Spot Viewed by Voyager I 30/30 Chandra Observatory Sees a Heart in the Darkness

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.

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.

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