Proposed 900-telescope array could detect an Earth-like exoplanet’s atmosphere in a single transit

What do you do when the observation you need comes around once a year? Well, preparation is key, but this is the awkward truth about finding another Earth. When a planet crosses the face of its star, a sliver of starlight passes through its atmosphere on the way to us, and the gases there absorb their own particular colors. Read the spectrum carefully and you can list what the air is made of: oxygen, ozone and water vapor, the things that would make you sit up.

For a genuine Earth-type planet orbiting a star like the sun, that signal amounts to roughly 1 part per million. It’s a very faint fingerprint on a very bright light. Astronomers have a standard answer to faint signals: Collect the same measurement repeatedly until the noise averages itself away.

It works beautifully for hot Jupiters, which whip around their stars every few days and hand you a fresh transit most weeks. But an Earth at an Earth-like distance from its star transits once per orbit, and an Earth-like orbit takes a year. Wait a decade and you have 10 attempts. Stacking is no longer the plan because each single transit has to be good enough on its own.

Which leaves aperture. You need to catch enough photons in those few hours, and that means a telescope around 30 meters across (98 feet), in space. JWST’s mirror is 6.5 meters (21 feet), it took decades, and it had to unfold itself on arrival in orbit.

Jian Ge and colleagues at Shanghai Astronomical Observatory, working with collaborators in China and Spain, have proposed an alternative.

Their concept, Life 2.0, is 900 1-meter telescopes (3.3 feet) flying as a distributed array. Each carries a miniature spectrograph and a very low-noise detector; each observes the transit independently, each is calibrated on its own, and the spectra are combined afterward. The result collects light like a 30-meter aperture (98 feet) without anybody having to build one.

The work is published on the arXiv preprint server.

The appeal is that identical detectors can be manufactured. A single vast mirror is a custom, slow-build process and terrifying if it gets dropped. Nine hundred identical 1-meter units (3.3 feet) are a production line, with lightweight silicon carbide mirrors and CMOS detectors. The waveguide spectrographs are not hypothetical, either, as prototypes have already reached 40% to 66% throughput.

The PLATO and China’s Earth 2.0 missions are being built to find the candidate worlds. Somebody has to be ready to look at them properly, and maybe this proposal is the way to do just that.

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

Full profile →

Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

Full profile →