Using Jupiter's Light Curves from the UV to the Mid-IR to Study the Light Curves on Brown Dwarfs and Direct-Imaging Planets
Abstract
It is suggested that the rotational modulations on brown dwarfs and direct-imaging planets are driven by the temperature perturbations and patchy clouds, but the underlying mechanism is not well understood. Here we analyze Jupiter's rotational light curves constructed from its global maps at 12 wavelengths from the UV to the mid-IR. The peak-to-peak amplitude of Jupiter's light curves at most wavelengths ranges from sub-percent level to 4%, but that at 5 μm exceeds 20%. The multi-wavelength light curves exhibit various kinds of shapes, time evolution and phase shifts between wavelengths. We find that Jupiter's rotational modulations are mainly caused by discrete patterns in the belts instead of in the zones. The light curve amplitude is dominated by the size and the brightness contrast of the Great Red Spot (GRS), the North Equatorial Belt (NEB) expansion, patchy clouds in the North Tropical Belt and the train of hot spots in the NEB. The reflection brightness contrast of the local patterns is controlled by distributions of tropospheric haze and clouds and chromophores in the clouds. The thermal emission brightness contrast is produced by distributions of temperature, tropospheric gas and clouds. Light curves in the methane absorption band at 0.89 μm exhibit significant phase shift compared with the UV and visible wavelengths. This phase shift is caused by the brightness change of the GRS at different wavelengths. At visible wavelengths, the GRS is a dark spot because of the chromophores in the GRS; In the CH4 band, the GRS is a bright spot because there is less CH4 above the GRS. This work sheds light on the underlying mechanism of the rotational modulations on brown dwarfs and direct-imaging planets. We suggest that distributions of the temperature, gas, and clouds are essential for the rotational modulations on brown dwarfs and exoplanets. At the wavelengths that the sensitive pressure level is above the cloud top, the opacity of the inhomogeneously distributed gas and temperature distributions are essential to the rotational modulation. The patchy cloud opacity is more likely to produce large photometric variability at the wavelengths of atmospheric windows. This project is supported by the NESSF.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5040201G