JWST detects dry ice in a planetary nebula for the first time

Astronomers have discovered carbon dioxide ice — commonly known as dry ice — inside a planetary nebula for the first time, using the James Webb Space Telescope to peer into the heart of NGC 6302, the Butterfly Nebula.

The finding, detailed in a paper published February 25 on the arXiv preprint server, challenges the assumption that planetary nebulae are too hostile for fragile molecular ices to survive. The research was led by Charmi Bhatt of the University of Western Ontario in Canada and involved an international team of 26 scientists from institutions across North America, Europe, and South America.

A Surprising Detection

NGC 6302, also called the Bug Nebula, is a bipolar planetary nebula located roughly 3,400 light-years from Earth in the constellation Scorpius. At its center lies the ancient core of a Sun-like star, surrounded by a massive dusty torus and bright lobes of expelled gas.

Using JWST's Mid-Infrared Instrument (MIRI), the team identified two absorption features characteristic of pure, crystalline carbon dioxide ice within the nebula's dusty torus. The ice absorption profile displayed a distinctive double-peak pattern between 14.9 and 15.3 micrometers, accompanied by cold gas-phase carbon dioxide at temperatures of 20 to 50 Kelvin along the same lines of sight.

Planetary nebulae are expanding shells of gas and dust shed by dying stars, and their environments are generally bathed in intense ultraviolet radiation — conditions long thought to destroy delicate ice molecules. The detection suggests the dense torus around NGC 6302's central star provides enough shielding for ice chemistry to persist.

Distinct Chemistry in a Dying Star's Envelope

The researchers found that the ratio of gas-phase to ice-phase carbon dioxide in NGC 6302 is more than an order of magnitude higher than what is typically observed in young stellar objects, according to the paper. This points to a fundamentally different ice formation or processing mechanism in evolved stellar environments compared to the cold molecular clouds and protoplanetary disks where ices are more commonly found.

The result builds on earlier JWST observations of NGC 6302 that revealed the presence of methyl cation and polycyclic aromatic hydrocarbons, suggesting the nebula hosts unexpectedly rich organic chemistry. The authors emphasized that future high-resolution observations of planetary nebulae will be essential to determine whether ice chemistry is common in dense nebular tori, or whether the Butterfly Nebula is an outlier.