Evolution of Neptune at Near-Infrared Wavelengths from 1994 through 2022

• Main Authors: Chavez, Erandi, de Pater, Imke, Redwing, Erin, Molter, Edward M, Roman, Michael T, Zorzi, Andrea, Alvarez, Carlos, Campbell, Randy, de Kleer, Katherine, Hueso, Ricardo, Wong, Michael H, Lynam, Elinor Gates Paul David, Davies, Ashley G, Aycock, Joel, Mcilroy, Jason, Pelletier, John, Ridenour, Anthony, Stickel, Terry
• Format: Journal Article
• Language: English
• Published: 16-07-2023
• Subjects: Physics - Earth and Planetary Astrophysics
• DOI: 10.48550/arxiv.2307.08157

Icarus Volume 404, 1 November 2023, 115667 Using archival near-infrared observations from the Keck and Lick
Observatories and the Hubble Space Telescope, we document the evolution of
Neptune's cloud activity from 1994 to 2022. We calculate the fraction of
Neptune's disk that contained clouds, as well as the average brightness of both
cloud features and cloud-free background over the planet's disk. We observe
cloud activity and brightness maxima during 2002 and 2015, and minima during
2007 and 2020, the latter of which is particularly deep. Neptune's lack of
cloud activity in 2020 is characterized by a near-total loss of clouds at
mid-latitudes and continued activity at the South Pole. We find that the
periodic variations in Neptune's disk-averaged brightness in the near-infrared
H (1.6 $\mu$m), K (2.1 $\mu$m), FWCH4P15 (893 nm), F953N (955 nm), FWCH4P15
(965 nm), and F845M (845 nm) bands are dominated by discrete cloud activity,
rather than changes in the background haze. The clear positive correlation we
find between cloud activity and Solar Lyman-Alpha (121.56 nm) irradiance lends
support to the theory that the periodicity in Neptune's cloud activity results
from photochemical cloud/haze production triggered by Solar ultraviolet
emissions.