Free Astronomy Magazine May-June 2025

41 MAY-JUNE 2025 ASTRO PUBLISHING o b s e r v e d with no fear of light contamina- tion or variability caused by a host star. And its short rotation pe- riod of just 2.4 hours makes it possible to survey very efficiently. Prior to the Webb observations, SIMP 0136 had been studied exten- sively using ground-based observa- tories and NASA’s Hubble and Spitzer space telescopes. “We already knew that it varies in brightness, and we were confident that there are patchy cloud layers that rotate in and out of view and evolve over time,” explained Allison McCarthy, doctoral student at Boston University and lead author on a study published in The Astro- physical Journal Letters . “We also thought there could be temperature variations, chemical reactions, and possibly some effects of auroral ac- tivity affecting the brightness, but we weren’t sure.” To figure it out, the team needed Webb’s ability to measure very pre- cise changes in brightness over a broad range of wavelengths. Using NIRSpec (Near-Infrared Spec- trograph), Webb captured thou- sands of individual 0.6- to 5.3- micron spectra — one every 1.8 sec- onds over more than three hours as the object completed one full rota- tion. This was immediately followed by an observation with MIRI (Mid- Infrared Instrument), which col- lected hundreds of spectroscopic measurements of 5- to 14-micron light — one every 19.2 seconds, over another rotation. The result was hundreds of detailed light curves, each showing the change in brightness of a very pre- cise wavelength (color) as different sides of the object rotated into view. “To see the full spectrum of this ob- ject change over the course of min- utes was incredible,” said principal investigator Johanna Vos, from Trin- ity College Dublin. “Until now, we only had a little slice of the near-in- frared spectrum from Hubble, and a few brightness measurements from Spitzer.” The team noticed almost immediately that there were several distinct light-curve shapes. At any given time, some wavelengths were growing brighter, while others were becoming dimmer or not changing much at all. A number of different factors must be affecting the bright-