JWST Measures the Atmosphere of an Exoplanet in the Habitable Zone

The James Webb Space Telescope is delivering exciting data again. This time it is not a distant image but the chemical signature of an alien world.

6.5 m JWST mirror

2021 JWST launched

5,000+ Known exoplanets

What was measured

When an exoplanet passes in front of its star, some starlight shines through its atmosphere. Individual gases absorb specific colors. From this pattern, researchers read the composition.

For the studied planet in the habitable zone, the spectra hint at water vapor. The measurement is still preliminary and must be confirmed.

How transmission spectroscopy works

The method uses a brief moment. Only during the transit does the atmosphere filter a tiny part of the starlight. This share is often below one hundredth of a percent.

The James Webb telescope is sensitive enough to measure this small effect. Its large mirror and infrared instruments are what make such observations possible at all.

Why water vapor is not yet life

Water vapor alone is no sign of life. It also occurs on lifeless worlds and says little about the surface. The real progress lies in the sensitivity of the method.

Only combinations of several gases count as possible biosignatures. Such patterns are far harder to measure and need many hours of observation.

Where the uncertainties lie

Stars are rarely calm. Spots and activity on the stellar surface can fake a signal that looks like an atmosphere. Researchers must carefully subtract this effect.

That is why every first measurement counts as preliminary. Only when independent observations show the same pattern does a hint become a finding.

What happens next

The team plans further transits of the same planet. More data shrink the error bars and test whether the water signal stays stable.

With better data, gases that are harder to explain could later be sought too. The question of life in space thus moves a small step closer, as the exoplanets section shows.

Frequently asked questions

Was life found?

No. Water vapor in an atmosphere is not a sign of life. It only shows the method is becoming sensitive enough for such molecules.

What is the habitable zone?

The habitable zone is the range of distances around a star where liquid water could exist on a surface. It is no guarantee of life, but it is seen as an interesting region to search.

How does JWST measure an atmosphere?

When a planet passes in front of its star, its atmosphere filters a tiny part of the starlight. From the absorbed colors the telescope reads off which gases are present.

Why is water vapor alone not proof of life?

Water vapor also occurs on lifeless worlds. Only certain combinations of several gases count as possible biosignatures, and those are far harder to measure.

How reliable is the measurement?

The measurement is preliminary. Starspots and activity can mimic an atmospheric signal, so further transits are needed before a hint becomes a confirmed result.

What can JWST do that earlier telescopes could not?

Its large 6.5-meter mirror and infrared instruments make the tiny changes in light measurable, which in transmission spectroscopy often lie below a hundredth of a percent.