Neon gas in protoplanetary disk SZ Chamaeleontis

In 2008 NASA’s Spitzer Space Telescope found a protoplanetary disk unlike any other. The dusty disk of gas surrounding the young Sun-like star SZ Chamaeleontis (SZ Cha) was being battered by extreme ultraviolet radiation – something previously seen only in computer models, never in the real universe. Planets in this system would have more time to form than in a disk being evaporated by X-rays, which is the norm. However, when the NASA/ESA/CSA James Webb Space Telescope followed up on SZ Cha, it found nothing out of the ordinary, as the ratio of neon II to III was within typical levels (no abundance of ultraviolet). In a short space of cosmic time, conditions in SZ Cha’s disk had changed, leaving astronomers to untangle meaning from the mismatched data and its implications for the formation of other solar systems.

This is significant because protoplanetary disks are the stuff of future planetary systems – and those potential planets are in a race against time. Astronomers use neon as an indicator of the dominant radiation hitting the disk and causing it to evaporate. When extreme ultraviolet light is dominant, there is more neon III. That is the unusual circumstance that Spitzer observed in 2008. Typically, a disk is dominated by X-ray radiation, which evaporates the disk more quickly, leaving planets less time to form.

Researchers think the dramatic differences in neon detections are the result of a wind that, when present, absorbs ultraviolet light and leaves X-rays to impact the disk. They will continue using Webb to find other examples of variability in disk conditions, working toward a better understanding of how planetary systems develop around Sun-like stars.