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Precipitation is expected in Titan's atmosphere, yet it has not been directly observed, and the geographical regions where rain occurs are unknown. Here we present near-infrared spectra from the Very Large Telescope and W. M. Keck Observatories that reveal an enhancement of opacity in Titan's troposphere on the morning side of the leading hemisphere. Retrieved extinction profiles are consistent with condensed methane in clouds at an altitude near 30 kilometers and concomitant methane drizzle below. The moisture encompasses the equatorial region over Titan's brightest continent, Xanadu. Diurnal temperature gradients that cause variations in methane relative humidity, winds, and topography may each be a contributing factor to the condensation mechanism. The clouds and precipitation are optically thin at 2.0 micrometers, and models of "subvisible" clouds suggest that the droplets are 0.1 millimeter or larger.

We report observations of the ro-vibronic a 1 ∆ → X 3 Σ − transition of SO at 1.707 µm on Io. These data were taken while Io was eclipsed by Jupiter, on four nights between July 2000 and March 2003. We analyze these results in conjunction with a previously published night to investigate the temporal behavior of these emissions. The observations were all conducted using the near-infrared spectrometer NIRSPEC on the W.M. Keck II telescope. The integrated emitted intensity for this band varies from 0.8 x 10 27 to 2.4 x 10 27 photons/sec, with a possible link to variations in Loki's infrared brightness. The band-shapes imply rotational temperatures of 550-1000K for the emitting gas, lending further evidence to a volcanic origin for sulfur monoxide. An attempt to detect the B 1 Σ → X 3 Σ − transition of SO at 0.97 µm was unsuccessful; simultaneous detection with the 1.707 µm band would permit determination of the SO column abundance.

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We observed (22) Kalliope and its companion Linus with the integral-field spectrograph OSIRIS, which is coupled to the adaptive optics system at the W.M. Keck 2 telescope on March 25 2008. We present, for the first time, component-resolved spectra acquired simultaneously in each of the Zbb (1-1.18µm), Jbb (1.18-1.42µm), Hbb (1.47-1.80µm), and Kbb (1.97-2.38µm) bands. The spectra of the two bodies are remarkably similar and imply that both bodies were formed at the same time from the same material; such as via incomplete re-accretion after a major impact on the precursor body.

Observations obtained with the near-infrared camera NIRC2, coupled to the adaptive optics system on the 10-m W.M. Keck II telescope on Mauna Kea, Hawaii, on 14 August 2007 revealed an active and highly-energetic eruption at Pillan at 245.2±0.7 °W and 8.5±0.5 °S. A onetemperature blackbody fit to the data revealed a (blackbody) temperature of 840 ± 40 K over an area of 17 km 2 , with a total power output of ~500 GW. Using Davies' (1996) Io Flow Model, we find that the oldest lava present is less than 1-2 hrs old, having cooled down from the eruption temperature of >1400 K to ~710 K; this young hot lava suggests that an episode of lava fountaining was underway. In addition to an examination of this eruption, we present data of the Pele and Pillan volcanoes obtained with the same instrument and telescope from 2002 through 2015. These data reveal another eruption at Pillan on UT 28 June 2010. Model fits to this eruption yield a blackbody temperature of 600-700 K over an area of ~60 km 2 , radiating over 600 GW. On UT 18 February 2015 an energetic eruption was captured by the InfraRed Telescope Facility (IRTF) via mutual event occultations. The eruption took place at 242.7±1 °W and 12.4±1 °S, i.e., in the eastern part of Pillan Patera. Subsequent observations showed a gradual decrease in the intensity of the eruption. Images obtained with the Keck telescope on 31 March and 5 May 2015 revealed that the locations of the eruption had shifted by 120-160 km to the NW. In contrast to the episodicity of Pillan, Pele has been persistent, observed in every appropriate 4.7 μm observation. Pele was remarkably consistent in its thermal emission from the Galileo era through February 2002, when a blackbody temperature of 940 ± 40 K and an area of 6.5 km was measured. Since that time, however, the radiant flux from this potentially large overturning lava lake has gradually subsided over the next decade by a factor of ~4, while the location of the thermal source was moving back and forth between areas roughly ~100 km to the W of the 2002 location, to an area roughly ~100 km to the SE of the 2002 location.

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