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What did the James Webb Space Telescope’s 11-hour observation of WISE 0855—the coldest known brown dwarf, about 7.4 light-years away, with a temperature near 265 kelvin (−8 °C), roughly twice Jupiter’s mass and nearly its size—reveal about its changing weather, including how NIRS
Webb found that WISE 0855’s atmosphere changes over hours: its infrared light varies in ways consistent with patchy water clouds changing thickness, alongside changes in gases brought up from deeper layers. The result was announced as the first confirmation of variable water clouds beyond the sola Webb found that WI...
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- Webb found that WISE 0855’s atmosphere changes over hours: its infrared light varies in ways consistent with patchy water clouds changing thickness, alongside changes in gases brought up from deeper layers. The result was announced as the first confirmation of *variable* water clouds beyond the sola
- Webb found that WISE 0855’s atmosphere changes over hours: its infrared light varies in ways consistent with patchy water clouds changing thickness, alongside changes in gases brought up from deeper layers. The result was announced as the first confirmation of *variable* water cl
- **What Webb measured:** On December 2, 2023, NIRSpec collected a spectrum about every 15 minutes over 11 hours. Brightness changed by up to 10% at some wavelengths; the largest variation was associated with carbon-monoxide absorption, not a 10% change at every wavelength. [13]
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Webb found that WISE 0855’s atmosphere changes over hours: its infrared light varies in ways consistent with patchy water clouds changing thickness, alongside changes in gases brought up from deeper layers. The result was announced as the first confirmation of variable water clouds beyond the solar system, but it is an inference from spectra and atmospheric models—not a photograph of clouds. 9
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- What Webb measured: On December 2, 2023, NIRSpec collected a spectrum about every 15 minutes over 11 hours. Brightness changed by up to 10% at some wavelengths; the largest variation was associated with carbon-monoxide absorption, not a 10% change at every wavelength.
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- How the team separated the effects: Different wavelengths probe different gases and atmospheric depths. Miles’s team interpreted part of the changing spectral pattern as uneven upper-atmosphere water-cloud cover rotating into view, while changes in carbon monoxide—and a less certain phosphine contribution—pointed to vertical mixing. Convection can lift gases into cooler layers faster than chemistry restores equilibrium, producing this “disequilibrium” signature. The exact cloud and gas contributions remain model-dependent.
- What was new: Earlier brightness measurements established that WISE 0855 varied, and Andrew Skemer’s 2016 Gemini North spectrum supplied evidence for water clouds, but neither tracked changing cloud thickness through a sequence of detailed spectra. Skemer is also a co-author of the Webb study, which grew out of the effort to obtain that time-resolved view.
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- Why its day length remains unknown: Features in the Webb data suggest roughly 5.4–5.6-hour timescales, whereas earlier Spitzer monitoring suggested about nine hours. A changing light pattern need not equal the body’s spin: clouds, winds or atmospheric waves can move and evolve, and an 11-hour record offers too few repeats to settle the difference. Observations exceeding 20 hours on multiple dates would help separate persistent rotation from moving weather and, by comparing wavelengths that probe different depths, build a three-dimensional picture of atmospheric motion.
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What is the short answer to "What did the James Webb Space Telescope’s 11-hour observation of WISE 0855—the coldest known brown dwarf, about 7.4 light-years away, with a temperature near 265 kelvin (−8 °C), roughly twice Jupiter’s mass and nearly its size—reveal about its changing weather, including how NIRS"?
Webb found that WISE 0855’s atmosphere changes over hours: its infrared light varies in ways consistent with patchy water clouds changing thickness, alongside changes in gases brought up from deeper layers. The result was announced as the first confirmation of *variable* water clouds beyond the sola
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Webb found that WISE 0855’s atmosphere changes over hours: its infrared light varies in ways consistent with patchy water clouds changing thickness, alongside changes in gases brought up from deeper layers. The result was announced as the first confirmation of *variable* water clouds beyond the sola Webb found that WISE 0855’s atmosphere changes over hours: its infrared light varies in ways consistent with patchy water clouds changing thickness, alongside changes in gases brought up from deeper layers. The result was announced as the first confirmation of *variable* water cl
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**What Webb measured:** On December 2, 2023, NIRSpec collected a spectrum about every 15 minutes over 11 hours. Brightness changed by up to 10% at some wavelengths; the largest variation was associated with carbon-monoxide absorption, not a 10% change at every wavelength. [13]