How many strange Earth-like planets lie beyond our solar system?

The search for Earth's twin continues, as scientists hunt for other hospitable worlds in the universe

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  The landmark discovery of Trappist-1 set off a wave of excitement across the space community. It was the first time multiple Earth-sized planets were found in a habitable zone and were orbiting the same star – Trappist-1. Courtesy: Nasa

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  All seven planets orbiting Trappist-1 are believed to be rocky and have potential for water on the surface. Courtesy: Nasa

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  Located in a habitable zone, Kepler-22b was labelled by Nasa as ‘super Earth’. Researchers believe the planet, which is larger than Earth, could be another ocean world. However, because of the planet’s extreme tilt, the north and south poles would experience sunlight and darkness for half a year each. Courtesy: Nasa

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  Discovered in 2020, Toi 700 d is only 20 per cent larger than Earth and orbits an M Dwarf star – a cool and stable type of star that do not release killer stellar flares, or radiation. Located 100 million light years away from Earth, one year on the planet is 37.4 days. Courtesy: Nasa

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  Discovered in 2011, KEPLER-20e is an Earth-size planet that orbits a sun-like star outside of the solar system. It is too close to its star to be in the habitable zone, so it cannot hold liquid water. However, the discovery was still groundbreaking because it was the first time small exoplanets were found to be orbiting around a star that was similar to the Sun. Courtesy: Nasa

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  Kepler-20f was discovered along with Kepler-20e. A year on the planet is19.6 days. Courtesy: Nasa

The search for extraterrestrial life has led scientists to find more than 4,000 planets as they try to locate one similar to Earth.

However, discovering hospitable worlds is not easy. The planet would need to have all the right ingredients for life and be in a habitable zone – a safe distance from its star, so liquid water could exist on the planet’s surface.

Nasa projects such as the Kepler Space Telescope and Transiting Exoplanet Survey Satellite have helped in many discoveries.

“The years and decades ahead will bring us ever closer to the ultimate in self-reflection: a mirror image of our own planet Earth. A small, rocky world with clouds, oceans and an atmosphere bearing signs of possible life,” Nasa said on its website.

“Such a world might be hundreds of light-years away, perhaps forever out of reach. But the molecular evidence we read in its atmosphere, using ever more acute technology, could give us the answer we've awaited since the dawn of humanity: no, we are not alone.”

The National highlights some of the fascinating discoveries of Earthlike planets made beyond the solar system

Trappist-1: a gold mine for space scientists

The discovery of Trappist-1 set off a wave of excitement across the space community.

It was the first time multiple Earth-sized planets were found in a habitable zone and were orbiting the same star – Trappist-1.

All seven planets are believed to be rocky and have potential for water on the surface.

Seven planets in the habitable zone are orbiting the Trappist-1 dwarf star, a cool star that does not emit dangerous levels of radiation. Courtesy: Nasa

Trappist-1, a cool dwarf star, was discovered in 1999. Scientists found three planets orbiting it in 2016, then four more planets were identified two years later.

"We now know more about Trappist-1 than any other planetary system apart from our own," Sean Carey, manager of the Spitzer Science Centre, said.

The planets are so close to each other that a person on the surface would be able to see neighbouring planets in the sky – appearing larger than how the Moon looks from Earth.

Kepler-22b: Earth’s twin

Located in a habitable zone, this exoplanet was labelled by Nasa as ‘super Earth’.

Researchers believe the planet, which is larger than Earth, could be another ocean world.

Kepler-22b is at a safe distance from its star. Courtesy: Nasa

Discovered in 2011, the exoplanet is at a safe distance from its star and could have a surface temperature of 15.5°C.

However, because of the planet’s extreme tilt, the north and south poles would experience sunlight and darkness for half a year each.

Scientists said the discovery was a major milestone in finding Earth’s twin.

"The tremendous growth in the number of Earth-size candidates tells us that we're honing in on the planets Kepler was designed to detect – those that are not only Earth-size, but also are potentially habitable," Natalie Batalha, Kepler deputy science team lead at San Jose State University, said.

"The more data we collect, the keener our eye for finding the smallest planets out at longer orbital periods."

Kepler-22b has a mass 36 times of Earth and takes 289.9 days to complete an orbit around its star.

TOI 700 d: 100 million light years from Earth

Discovered in 2020, TOI 700 d is only 20 per cent larger than Earth and orbits an M Dwarf star – a cool and stable type of star that does not release killer stellar flares, or radiation.

The Toi 700 d exoplanet is in the habitable zone. Courtesy: Nasa

However, the planet is tidally locked to its star, like how the Moon is to the Earth, which means only one side gets daylight and its cloud formations and wind patterns could be much different.

One year on the planet is 37.4 days.

Discovered by Nasa’s Transiting Exoplanet Survey Satellite, TOI 700 d is 100 million light years away from Earth.

Kepler-20e/Kepler-20f: orbiting a star like the Sun

Discovered in 2011, Kepler-20e and Kepler-20f are Earth-size planets that orbit a sun-like star outside the solar system.

They are too close to their star to be in the habitable zone and cannot hold liquid water.

However, their discovery was still groundbreaking because it was the first time small exoplanets were found to be orbiting around a star that was similar to the Sun.

The Kepler-20e and Kepler-20f size compared with Venus and Earth. Courtesy: Nasa

Kepler-20e is 0.87 times the radius of Earth and the other planet is 1.03 times its radius – slightly larger than Earth.

Both have very short orbital periods around their stars – Kepler-20e completes one full circle in 6.1 days, while Kepler-20f takes 19.6 days.

“This discovery demonstrates for the first time that Earth-size planets exist around other stars, and that we are able to detect them,” Francois Fressin, lead author of the study that published the findings, said when the planets were first discovered.

The rocky planets are too hot to be habitable. Kepler-20f is as hot as Mercury at 426°C and the surface temperature on Kepler-20e is 760°C – hot enough to melt glass.

30 incredible images of the UAE from space - in pictures

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  The UAE (centre-right) is well-lit during the night and is very visible from space. This image was captured from the International Space Station. Nasa

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  Nasa astronaut Jessica Meir shared this image of Abu Dhabi two months after Emirati astronaut Hazza Al Mansouri returned to Earth from the space station. Jessica Meir Twitter

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  A stunning image of Downtown Dubai taken in 2012 by the Pleiades satellite. The Burj Khalifa is visible. European Space Agency

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  The largest mosque in Sharjah captured by Emirati satellite KhaliafSat. Mohammed bin Rashid Space Centre

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  An image of Al Ain in 1984, when there was not a lot of greenery. Abu Dhabi emirate is now considered a green oasis with a major focus in agriculture. Nasa's Earth Observatory

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  The Mohammed bin Rashid Space Centre counted 45,000 palm trees in Al Ain. The satellite images are helping to monitor the quantity and health of thousands of trees. MBRSC

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  Umm Al Quwain, one of the seven emirates of the UAE, seen from space. The emirate is on a peninsula and has many attractive sites, including ancient forts. Zoom Earth

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  The Corniche Park in Umm Al Quwain (top) and Municipal Park on the bottom side of the image. Zoom Earth

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  KhalifaSat captured Jebel Jais, the highest summit in the UAE which is about 2,000 metres above sea level. It also has the world’s longest zipline. MBRSC

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  Fujairah is on the east coast of the UAE and is known for its beaches and the Hajar mountains. The mountainous areas are visible in this image, as well as the Fujairah International Airport and the Port Fujairah on the top right. Zoom Earth

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  Abu Dhabi’s Sir Bani Yas Island captured from space in 2010. The island is a major tourist attract with a mix of wildlife, archaeological sites and luxury hotel retreats. Nasa

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  Dubai seen from the International Space Station. Nasa

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  The Strait of Hormuz separates the UAE and Iran. Nasa

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  The UAE captured from space in 2013. Nasa’s Earth Observatory

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  Hazza Al Mansouri took this photo of Umm Ghafa in Al Ain from the space station in 2019. It is the village where his colleague and reserve astronaut Sultan Al Neyadi grew up. Sultan Al Neyadi twitter

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  The Dubai Expo site captured by KhalifaSat in 2019. The much-anticipated event is set to begin on October 1, 2021. MBRSC

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  The man-made Love Lake in Dubai’s Al Qudra desert. MBRSC

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  Dust blows over the Arabian Gulf in 2013. The UAE is on the right side of this image and Saudi Arabia is on the left. Nasa’s Earth Observatory

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  A dust plume over the UAE in 2009. Nasa

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  The Sheikh Khalifa bin Zayed Al Nahyan Mosque in Al Ain captured by KhalifaSat. It features a magnificent dome, which measures 86 metres in diameter. MBRSC

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  The Copernicus Sentinel 2 mission captured this striking view of Abu Dhabi from space. The dark green patch of land is the Mangrove National Park. Ferrari World can be seen in the centre-right of the image. European Space Agency

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  An incredible view of the UAE captured by Hazza Al Mansouri in 2019. Hazza Al Mansouri twitter

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  An image of Abu Dhabi taken from the International Space Station as it orbited 423 kilometres above Oman. Nasa

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  Planes can be seen parked at Dubai International Airport during the Coronavirus Pandemic in May 2020, when travel was restricted. MBRSC

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  KhalifaSat captured this stunning image of Abu Dhabi in 2020. MBRSC

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  Another view of the UAE’s capital city of Abu Dhabi from space. MBRSC

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  One of the most recent photos of Dubai taken in 2020 from space, showing the Palm Jumeirah, Palm Jebel Ali and the World Islands. MBRSC

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  Mangroves, salt domes, salt flats and coral reefs on the south-west coast of the UAE, near Abu Dhabi, captured in 2001. Nasa’s Earth Observatory

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  The first image captured by KhalifaSat in 2018. It is the Palm Jumeirah in Dubai. MBRSC

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  A manufacturing site on the Arabian Gulf coast of the UAE, near Abu Dhabi. Nasa