Determine the rotation period of WISE 0855

Determine the exact rotation period of the brown dwarf WISE 0855 from observations with a sufficiently long temporal baseline.

Background

The paper analyzes 11 hours of JWST/NIRSpec time-series spectroscopy together with previously published Spitzer photometry. Significant power appears near 5.4–5.6 hours in the JWST data, while some Spitzer epochs show different or longer periods. Because the observations do not cover enough complete rotations and do not yield a consistent periodicity across epochs, the authors identify the exact rotation period as unresolved. Establishing this period is necessary for interpreting the observed atmospheric modulations and distinguishing rotational variability from evolving atmospheric structures.

References

WISE 0855 has shown amplitude modulations on timescales between $\sim$5 and 10 hours, but the exact rotation period of WISE 0855 is still unknown.

— Water Cloud and Chemical Modulations in the Coldest Brown Dwarf  (2609.20664 - Miles et al., 17 Sep 2026) in Section 4.2, “Periodicity of WISE 0855 and Long-Term Variability”; reiterated in Section 8, “Summary”