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Researchers in China have completed the concept study for a 6-metre (20-foot) space telescope to examine the atmosphere of nearby Earth-like planets and search for signs of life with unprecedented precision.
If selected to enter the design phase, the HABItable Terrestrial planetary ATmospheric Surveyor – or Habitats – will join the global race to find a twin of planet Earth.
With a potential price tag of over 10 billion yuan (US$1.48 billion), it will also be the most ambitious and expensive space science project China has ever funded.
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Thanks to telescopes such as Kepler and TESS surveying the sky for planets outside the solar system, humanity has discovered more than 5,000 exoplanets and edged ever closer to answering the question “are we alone in the universe?”
But the details of those exoplanets remain extremely difficult to observe as their parent star often outshines them by billions of times in a sun-Earth-like system.
A powerful space telescope like the James Webb can detect water molecules in an exoplanet’s atmosphere with the precision of about 100 parts per million (ppm).
That would need to get to 0.0001 ppm for scientists to characterise the atmosphere of an Earth-sized rocky planet orbiting a sun-like star in a potentially habitable zone, according to Wang Wei from the National Astronomical Observatories in Beijing.
While future missions are being planned in Europe and the United States, Chinese scientists also want to be part of the next round of the search.
China is a latecomer to exoplanet research and space telescopes, but it has caught up quickly with the development of a 2-metre Hubble-like space telescope under way, which will fly with the country’s space station in 2024.
For Habitats – also known as Tianlin, or “neighbours of heaven” – Wang’s team proposed a three-mirror system with a main mirror as wide as 6 to 6.5 metres. It will join the James Webb at the so-called sun-Earth L2 point, 1.5 million km (932,000 miles) away from Earth, for a highly stable observation environment.
“We will be looking for the so-called biosignature molecules including water (H2O), oxygen (O2), ozone (O3), and methane (CH4) in the atmosphere of Earth-like planets orbiting sun-like stars,” said Wang, who led the concept study.
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While water and oxygen molecules are easily detectable and essential to the formation of life, the search for by-products of biological activities such as ozone and methane were equally important, he said.
Each type of molecule emits a unique spectral line that can be detected by an optical instrument on the telescope called a spectrometer.
To collect as many spectra as possible, the team decided to expand the main mirror’s size from 4 to 6 metres. “This way, the telescope will be able to see more, fainter exoplanets, and its precision is expected to reach 0.0001 ppm,” Wang said.
The team estimates that Habitats will be able to obtain the spectrum of more than 20 candidate exoplanets during the telescope’s first five years of operation.
They are also hoping to find signs of life on the surface of those rocky planets. “If the weather is clear enough, we might be able to receive reflected signals if the planet is covered with plantation or bacteria,” he said.
It is an ambitious project that will face multiple technical challenges, including developing a satellite platform that can support the telescope to point precisely at a remote, dim planet for hundreds of hours of continuous observation.
Since the mirrors are not foldable, a Long March 9 super-heavy rocket is likely to be needed to send Habitats into orbit.
That rocket is currently under development but should be ready in time for a potential target launch date for the space telescope of between 2035 and 2040.
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Meanwhile, Nasa is considering merging two of its mission concepts – one dubbed HabEx and the other Luvoir – for similar purposes to Habitats and to be launched in the early 2040s, with a budget of at least US$10 billion.
“As humanity approaches the first opportunity to finally find and understand a planet like our own, Chinese scientists will need to work hard for a front row seat,” Wang said.
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