Neptune's Dynamic Atmosphere from Kepler K2 Observations: Implications for Brown Dwarf Light Curve Analyses

TL;DR

This study analyzes Neptune's atmosphere using Kepler K2 data and high-resolution imaging, validating cloud feature tracking and offering insights into atmospheric variability relevant to brown dwarf and exoplanet studies.

Contribution

It provides a direct comparison between light curve data and imaging to validate cloud feature analysis and discusses implications for substellar atmospheric variability.

Findings

Large discrete storms dominate Neptune's light curves.

Cloud variability occurs on short and long timescales.

Atmospheric stability may depend on the size and number of features.

Abstract

Observations of Neptune with the Kepler Space Telescope yield a 49-day light curve with 98% coverage at a 1-minute cadence. A significant signature in the light curve comes from discrete cloud features. We compare results extracted from the light curve data with contemporaneous disk-resolved imaging of Neptune from the Keck 10-meter telescope at 1.65 microns and Hubble Space Telescope visible imaging acquired 9 months later. This direct comparison validates the feature latitudes assigned to the K2 light curve periods based on Neptune's zonal wind profile, and confirms observed cloud feature variability. Although Neptune's clouds vary in location and intensity on short and long time scales, a single large discrete storm seen in Keck imaging dominates the K2 and Hubble light curves; smaller or fainter clouds likely contribute to short-term brightness variability. The K2 Neptune light curve, in conjunction with our imaging data, provides context for the interpretation of current and future brown dwarf and extrasolar planet variability measurements. In particular we suggest that the balance between large, relatively stable, atmospheric features and smaller, more transient, clouds controls the character of substellar atmospheric variability. Atmospheres dominated by a few large spots may show inherently greater light curve stability than those which exhibit a greater number of smaller features.