China is hatching a plan to find Earth 2.0


China is planning its first space mission to study the sky for exoplanets similar to Kepler-186f, a planet the size of Earth orbiting a distant star (artist’s impression). Credit: NASA Ames / JPL-Caltech / T. Pyle

After sending robots to the Moon, landing them on Mars and building its own space station, China is now looking at distant solar systems. This month, scientists will release detailed plans for the country’s first mission to discover exoplanets.

The mission will aim to study planets outside the Solar System in other parts of the Milky Way with the aim of finding the first Earth-like planet orbiting the habitable zone of a star like the Sun. Astronomers believe that such a planet, called an Earth 2.0, would have the right conditions for liquid water – and possibly life – to exist.

More than 5,000 exoplanets have already been discovered in the Milky Way, most with NASA’s Kepler telescope, which was in use for 9 years before running out of fuel in 2018. Some of the planets were rock-filled Earth-like bodies orbiting small reds. dwarf stars, but none fit the definition of an Earth 2.0.

With current technology and telescopes, it is extremely difficult to find the signal from small, Earth-like planets when their host stars are a million times heavier and a billion times brighter, says Jessie Christiansen, astrophysicist at NASA Exoplanet Science Institute in California. Institute of Technology in Pasadena.

The Chinese mission, called Earth 2.0, hopes to change that. It will be funded by the Chinese Academy of Sciences and is nearing completion of its early design phase. If the designers pass a review by a panel of experts in June, the mission team will receive funding to begin building the satellite. The team plans to launch the spacecraft on a Long March rocket by the end of 2026.

Seven eyes

The Earth 2.0 satellite is designed to carry seven telescopes that will observe the sky for four years. Six of the telescopes will work together to survey the Cygnus-Lyra constellations, the same part of the sky that the Kepler telescope searched. “The Kepler field is a low-hanging fruit because we have very good data from it,” said Jian Ge, an astronomer leading the Earth 2.0 mission at the Shanghai Astronomical Observatory at the Chinese Academy of Sciences.

The telescopes will look for exoplanets by detecting small changes in a star’s brightness that indicate that a planet has passed in front of it. Using several small telescopes together gives scientists a wider field of view than a single large telescope like the Kepler. Earth 2.0’s 6 telescopes together will stare at about 1.2 million stars across a 500-square-degree part of the sky, which is about 5 times wider than Kepler’s vision was. At the same time, Earth 2.0 will be able to observe weaker and more distant stars than NASA’s Transiting Exoplanet Survey Satellite (TESS), which examines bright stars near Earth.

“Our satellite may be 10-15 times more powerful than NASA’s Kepler telescope in its space exploration capability,” says Ge.

The satellite’s seventh instrument will be a gravitational microlens telescope to study rogue planets – free-moving celestial bodies orbiting any star – and exoplanets far from their star, which looks like Neptune. It will detect changes in starlight when the gravity of a planet or star distorts the light from a background star as it passes in front of it. The telescope will target the center of the Milky Way, where a massive number of stars are located. If launched successfully, this would be the first gravitational microlens telescope operating from space, Ge says.

“Our satellite can essentially perform a census that identifies exoplanets of different sizes, masses and ages. The mission will provide a good collection of exoplanet samples for future research,” he says.

Doubling of data

NASA launched Kepler in 2009 with the aim of finding out how common Earth-like planets are in the galaxy. To confirm that an exoplanet is Earth-like, astronomers must measure the time it takes to orbit its sun. Such planets should have an orbital period similar to Earth’s and pass their suns about once a year. Chelsea Huang, an astrophysicist at the University of Southern Queensland in Toowoomba, says scientists need at least three transits to calculate an exact orbital period that takes about three years of data, and sometimes more if there are data gaps.

But four years inside the Kepler mission, parts of the instrument failed, making the telescope unable to stare at part of the sky for an extended period of time. Kepler was on the verge of finding some truly Earth-like planets, says Huang, who has worked with the Earth 2.0 team as a data simulation consultant.

With Earth 2.0, astronomers could have an additional four years of data that, when combined with Kepler’s observations, could help confirm which exoplanets are truly Earth-like. “I’m very excited about the prospect of returning to the Kepler field,” says Christiansen, who hopes to study Earth 2.0 data if made available.

Ge hopes to find a dozen Earth 2.0 planets. He says he plans to publish the data within a year or two of their collection. “There will be a lot of data so we need all the hands we can get,” he says. The team already has about 300 scientists and engineers, mostly from China, but Ge hopes more astronomers around the world will join. “Earth 2.0 is an opportunity for better international cooperation.”

The European Space Agency is also planning an exoplanet mission – called the Planetary Transits and Oscillations of Stars (PLATO) – which is scheduled to be launched in 2026. PLATO’s design has 26 telescopes, which means it will have a much larger field of view than Earth 2.0. But the satellite will change gaze every two years to observe different areas of the sky.

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