Keck Near-Infrared Detections of Mab and Perdita

• Main Authors: Molter, Edward M, de Pater, Imke, Moeckel, Chris
• Format: Journal Article
• Language: English
• Published: 25-07-2023
• Subjects: Physics - Earth and Planetary Astrophysics
• DOI: 10.48550/arxiv.2307.13773

Icarus, Volume 405, 2023, 115697, ISSN 0019-1035 We report the first near-infrared detection of Uranus's tiny moon Mab, the
presumed source of the blue and diffuse $\mu$ ring, using the NIRC2 instrument
at Keck Observatory. The detection was permitted by an updated shift-and-stack
procedure allowing us to integrate on Mab as it moved across the detector in 23
separate exposures taken over $\sim$2 hours, as well as the very low
(0.02$^{\circ}$) phase angle at the time of observation. At this phase angle,
Mab has an integrated I/F of 24 $\pm$ 3 km$^2$ at 1.6 $\mu$m and $\lesssim$37
km$^2$ at 2.1 $\mu$m. Comparing these values with Mab's visible reflectance as
derived by HST reveals that Mab is spectrally blue; its (0.5 $\mu$m)/(1.6
$\mu$m) color is more consistent with Miranda's value than Puck's value. Mab is
therefore more likely a $\sim$6-km radius body with a Miranda-like surface than
a 12-km radius body with a Puck-like surface, in agreement with prior work
based on infrared upper limits, but we caution that a Puck-like color is only
ruled out at the 2$\sigma$ level. We also report the first infrared photometry
of Perdita, finding an integrated I/F of 31 $\pm$ 3 km$^2$ at 1.6 $\mu$m.