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STARSStories

2022

A breath taken at 4.05 microns

A space telescope watches a Saturn-mass world cross its star. In the missing starlight: water, carbon dioxide, and sulfur dioxide made by starlight itself.

Lagrange Point 2, looking at WASP-39

SCIENTIFIC FIGURENo painted planet. WASP-39b is inferred from a transmission spectrum. JWST saw starlight filtered through an atmosphere, not a landscape.

The filter

WASP-39b crosses its sun. A little of the starlight passes through the planet’s air. JWST, at L2, spreads that missing light into a spectrum. Water is there. Carbon dioxide is there. At 4.05 microns a feature is identified as sulfur dioxide, a molecule that, at this temperature, is not expected in equilibrium. Starlight has cooked the air. Photochemistry.

Hundreds of scientists, one telescope, a planet no one will walk. The destination is still only a spectrum. That is already a kind of going: we are reading weather we cannot stand in.

ASTRONOMY

Transmission spectroscopy is Kirchhoff’s method moved off the Sun. A dark line, once sodium in Heidelberg, is now a molecule in another system. The star is still the lamp. The world is the filter. Payne’s hydrogen stars have planets whose air we can, at last, name by wavelength.

Question

What remains of going, when the first air we taste is a missing color in a star?

Sources

Also this sky