WASHINGTON, July 21 — The James Webb Space Telescope has already rewritten the rulebook on how we study planets far beyond our solar system. But its next big challenge? Sniffing the air of a world barely bigger than our own.
Launched on December 25, 2021, Webb has quickly become the go-to tool for exoplanet atmosphere characterization. Its Near-Infrared Spectrograph (NIRSpec) and Mid-Infrared Instrument (MIRI) can pick out molecules like water, methane, carbon dioxide, and ammonia floating in a planet’s atmosphere.
It does this using a technique called transmission spectroscopy — think of it like holding a prism up to a star’s light as it filters through a planet’s air. Each molecule leaves a unique fingerprint in the spectrum. In 2022, Webb made headlines by spotting carbon dioxide in the atmosphere of the hot Jupiter WASP-39b.
That was a big first. But now astronomers have their sights set on something much smaller: an Earth-sized planet orbiting a faint star.
And here’s where the challenge gets real. In plain terms, a big, puffy planet like WASP-39b is easy to read. It blocks a lot of starlight, and its thick atmosphere leaves a strong signal.
A rocky, Earth-sized world? That’s a whisper in a stadium. The signal is tiny.
To get a detectable reading, Webb would need to watch the planet cross in front of its star multiple times — at least ten transits. The practical upshot?
This isn’t a quick snapshot. It’s a long observing campaign, spread out over many orbits. But the payoff could be enormous: the first confirmed atmosphere on a planet close to Earth’s size.
So when could this happen? Observations could have been scheduled as early as 2025, according to the mission’s planning timelines.
Whether those observations are already in the pipeline or still waiting for telescope time, Webb’s expected operational lifetime of at least ten years gives plenty of room to look.
What if there’s nothing there?
That outcome might sound like a letdown, but scientists see a silver lining. If no atmosphere is detected, the planet becomes a laboratory for studying airless rocky worlds orbiting nearby stars. Think of it like our Moon — a bare rock bathed in stellar radiation, stripped of any protective envelope.
That’s a valuable data point too, especially when we’re trying to understand how common Earth-like environments really are. We know Webb can detect carbon dioxide, methane, water, and ammonia.
We’ve seen it work on a giant. Now the telescope is being asked to do the same for a world that barely makes a dent in its star’s light. It’s the kind of observation that pushes the limits of what the telescope was designed for.
And that’s the real story here. Webb wasn’t just built to take pretty pictures.
Its instruments were designed to read the chemistry of distant worlds. With at least a decade of fuel and a suite of sensitive tools, the telescope is now the premier facility for this kind of work. Each transit observation is a careful, painstaking peek into another world’s air — and we’re just getting started.
Sources
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