Original title: WINERED Detects a Strong Atmospheric Outflow on the Sub-Neptune GJ 3090b
Shreyas Vissapragada, Zifan Lin, Annabella Meech, Collin Cherubim +11 · September 2026
Sub-Neptunes are common planets orbiting close to their stars, but scientists still puzzle over how they evolve and what they are made of. To learn more, astronomers watched the sub-Neptune GJ 3090b cross in front of its star during two transits. As starlight passes through the outer atmosphere of a planet, escaping gases like helium absorb specific colors. By tracking this energized helium, researchers can watch an atmosphere bleed out into space. They used the WINERED instrument and spotted a strong, variable helium signal without a significant velocity shift. This implies stellar light is driving photoevaporation, where intense radiation boils the upper gas away. The team found that GJ 3090b has an atmospheric lifetime of ~300 Myr, far shorter than older estimates. Now about ~1 Gyr old, this adolescent world is rapidly losing its outer envelope.
You buy a helium balloon and expect it to float for a month. But after just two days, it's nearly deflated, much faster than promised. Something is making the gas escape faster than normal. In this paper, the planet's atmosphere leaks helium much faster than models predicted—just like the balloon leaking faster than expected.
This discovery shows that some sub-Neptune planets can lose their atmospheres at dramatically faster rates than previous models assumed. It helps astronomers understand how common planets like these evolve and whether they formed with different compositions. For the search for habitable worlds, it shows that atmospheric escape can reshape a planet's future on timescales of less than a billion years.
The abstract notes that the first transit was affected by a stellar flare, complicating the signal, and only the second transit was clean. The amplitude variation is observed but not fully explained. The atmospheric metallicity constraint is an upper limit, and the presence of aerosols in the lower atmosphere is inferred rather than directly measured. The lifetime estimate depends on outflow modeling assumptions.
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WINERED Detects a Strong Atmospheric Outflow on the Sub-Neptune GJ 3090b — Shreyas Vissapragada, Zifan Lin, Annabella Meech et al.
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.