Abstract
Abstract Rotational modulations are observed on brown dwarfs and directly imaged exoplanets, but the underlying mechanism is not well understood. Here we analyze Jupiter’s rotational light curves at 12 wavelengths from the ultraviolet (UV) to the mid-infrared (mid-IR). The peak-to-peak amplitudes of Jupiter’s light curves range from subpercent to 4% at most wavelengths, but the amplitude exceeds 20% at 5 μm, a wavelength sensing Jupiter’s deep troposphere. Jupiter’s rotational modulations are primarily caused by discrete patterns in the cloudless belts instead of the cloudy zones. The light-curve amplitude is controlled by the sizes and brightness contrasts of the Great Red Spot (GRS), expansions of the North Equatorial Belt (NEB), patchy clouds in the North Temperate Belt (NTB), and a train of hot spots in the NEB. In reflection, the contrast is controlled by upper tropospheric and stratospheric hazes, clouds, and chromophores in the clouds. In thermal emission, the small rotational variability is caused by the spatial distribution of temperature and opacities of gas and aerosols; the large variation is caused by the NH3 cloud holes and thin-thick clouds. The methane-band light curves exhibit opposite-shape behavior compared with the UV and visible wavelengths, caused by a wavelength-dependent brightness change of the GRS. Light-curve evolution is induced by periodic events in the belts and longitudinal drifting of the GRS and patchy clouds in the NTB. This study suggests several interesting mechanisms related to distributions of temperature, gas, hazes, and clouds for understanding the observed rotational modulations on brown dwarfs and exoplanets.
Highlights
Rotational photometric variabilities have been observed on brown dwarfs (e.g., Radigan et al 2012; Yang et al 2016; Apai et al 2017), exoplanets (Zhou et al 2016), and solar system gas giants (e.g., Gelino & Marley 2000; Karalidi et al 2015; Simon et al 2016)
We use the global maps of Jupiter in reflected sunlight obtained during the Outer Planets Atmosphere Legacy (OPAL) program by the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) (Simon et al 2015)
One can see the rotational variations caused by the Great Red Spot (GRS), North Equatorial Belt (NEB) expansion event, and hot spots in the light-curve contribution map (Figure 3)
Summary
Rotational photometric variabilities have been observed on brown dwarfs (e.g., Radigan et al 2012; Yang et al 2016; Apai et al 2017), exoplanets (Zhou et al 2016), and solar system gas giants (e.g., Gelino & Marley 2000; Karalidi et al 2015; Simon et al 2016). The distributions of deep H2O clouds (8–5 bars), NH4HS (2–1.5 bars), and NH3 clouds (0.7–0.3 bars) in the troposphere (West et al 2004); hazes in the upper troposphere and stratosphere; and chromophores in and above the NH3 clouds have all been well observed and studied for decades (e.g., Ferris & Ishikawa 1987; Taylor et al 2004; West et al 2004; Carlson et al 2016; Sromovsky et al 2017) These data allow us to thoroughly investigate the underlying mechanism of the rotational light curves of Jupiter in thermal emission and quantify the important roles of temperature, gas, and clouds.
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