With hundreds of active volcanoes varying in intensity on different timescales, Jupiter's moon Io is the most volcanically active body in the solar system. Io has been observed from Earth using high-cadence near-infrared photometry during occultations by Jupiter and other Galilean moons since the 1980s. These observations encode a wealth of information about the volcanic features on its surface. We built a generative model for the observed occultation light curves using the code starry, which enables fast, analytic, and differentiable computation of occultation light curves in emitted and reflected light. Using this model, we are able to recover surface thermal emission maps of Io containing known volcanic hot spots without having to make assumptions about the locations, shapes, or number of hot spots. Our model is also directly applicable to the problem of mapping the surfaces of stars and exoplanets.

We present observations of five stellar occultations for (11351) Leucus and reports from two efforts on (21900) Orus. Both objects are prime mission candidate targets for the Lucy Discovery mission. Combined results for Leucus indicate a very dark surface with p V = 0.037 ± 0.001, which is derived from the average of the multichord occultations. Our estimate of the triaxial ellipsoidal shape is for axial diameters of 63.8 × 36.6 × 29.6 km assuming that the spin pole is normal to the line of sight. The actual shape of the object is only roughly elliptical in profile at each epoch. Significant topography is seen with horizontal scales up to 30 km and vertical scales up to 5 km. The most significant feature is a large depression on the southern end of the object as seen from a terrestrial viewpoint. For this work we developed a method to correct for differential refraction, accounting for the difference in color between the target object and the reference stars for astrometry derived from ground-based images.

Observations from field remote sensing of the morphology, kinematics and temperature of the Marum/Mbwelesu lava lake in the Vanuatu archipelago in 2014 reveal a highly active, vigorously erupting lava lake. Active degassing and fountaining observed at the ~50m lava lake led to large areas of fully exposed lavas and rapid (~5m/s) movement of lava from the centers of upwelling outwards to the lake margins. These rapid lava speeds precluded the formation of thick crust; there was never more than 30% non-translucent crust. The lava lake was observed with several portable, handheld, low-cost, near-infrared imagers, all of which measured temperatures near 1000°C and one as high as 1022°C, consistent with basaltic temperatures. Fine-scale structure in the lava fountains and cooled crust was visible in the near infrared at ~5cm/pixel from 300m above the lake surface. The temperature distribution across the lake surface is much broader than at more quiescent lava lakes, peaking ~850°C, and is attributed to the highly exposed nature of the rapidly circulating lake. This lava lake has many characteristics in common with other active lava lakes, such as Erta Ale in Ethiopia, being confined, persistent and high-temperature; however it was much more active than is typical for Erta Ale, which often has >90% crust. Furthermore, it is a good analogue for the persistent, high-temperature lava lakes contained within volcanic depressions on Jupiter's moon Io, such as Pele, also believed from spacecraft and ground-based observations to exhibit similar behavior of gas emission, rapid overturn and fountaining.

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 degrees W and 8.5 +/- 0.5 degrees S. A one-temperature 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 similar to 500 GW. Using Davies' (Davies, A.G. [1996]. Icarus 124(1), 45-61) Io Flow Model, we find that the oldest lava present is less than 1-2 h old, having cooled down from the eruption temperature of >1400 K to similar 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 similar to 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 degrees W and 12.4 +/- 1 degrees 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 mu m 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(2) was measured. Since that time, however, the radiant flux from what is likely a apparently large, overturning lava lake has gradually subsided over the next decade by a factor of similar to 4, while the location of the thermal source was moving back and forth between areas roughly similar to 100 km to the W of the 2002 location and an area roughly similar to 100 km to the SE of the 2002 location. (C) 2015 Elsevier Inc. All rights reserved.

We documented eruption activity at three primary vents at Yasur volcano, Tanna Island, Vanuatu using portable instrumentation in the field over a period of 5h on 21 May 2014, and acquired aerial images of the craters and vents on 22 May 2014. Although limited in duration, our observations of eruption intervals, durations, temperatures, and speeds of ejected material illustrate the characteristics of the activity at the time at each of the primary vents, providing a useful snapshot of eruption behavior and revealing continued variability at Yasur in comparison to other observation campaigns. Hand-held, high-resolution, near-infrared observations of one of the vents gave peak temperatures of 850°C to 930°C for ejected clasts, with a maximum temperature of 1033°C. These temperatures are significantly higher than previous measurements because exposed lavas could be resolved at timescales less than a second. Our aerial near-infrared images allowed us to estimate the combined area of the active vents within the crater to be ~150m2, and comparison to MODIS radiance measurements in the same time frame yields temperatures, averaged over the combined vent area, of 530–730°C. In the context of previous observations at Yasur, the activity in May 2014 exhibited lower overall intensity, as well as differences in the nature of the eruptions at the various vents, providing insight regarding the temporal variability of Yasur's activity.

We describe how near-field audio recording using a pocket digital sound recorder can usefully document volcanic activity, demonstrating the approach at Yasur, Vanuatu in May 2014. Prominent emissions peak at 263Hz, interpreted as an organ-pipe mode. High-pass filtering was found to usefully discriminate volcano vent noise from wind noise, and autocorrelation of the high pass acoustic power reveals a prominent peak in exhalation intervals of ~2.5, 4 and 8s, with a number of larger explosive events at ~200s intervals. We suggest that this compact and inexpensive audio instrumentation can usefully supplement other field monitoring such as seismic or infrasound. A simple estimate of acoustic power interpreted with a dipole jet noise model yielded vent velocities too low to be compatible with pyroclast emission, suggesting difficulties with this approach at audio frequencies (perhaps due to acoustic absorption by volcanic gases).

In July 2007, we observed a stellar occultation by Pluto from three sites in New Zealand and Australia. From these occultation observations, we find that Pluto's atmospheric pressure is still at the increased level measured in 2002 and 2006 with a pressure at a radius of 1275 km of 2.09 +/- 0.09 mu bar. One of the sites, Mt. John Observatory, was similar to 70 km from the shadow center and we recorded the first central-flash occultation by Pluto. We carried out a dual-wavelength observation from this site with two different cameras using filtered high-time resolution observations in the visible from the one-meter telescope at Mt. John Observatory. From our central-flash observations, we find the elliptical shape that best matches the data corresponds to a nearly prolate atmosphere with an ellipticity of 0.09. The flux observed in the central-flash data can be fit equally well with either a haze layer or a thermal gradient in the altitudes probed by the occultation. However, the star light contributing to the central-flash occultation for the haze layer model would pass through a radius of 1130 km from Pluto's center. Given our current best estimate of Pluto's surface radius is greater than 1151 km (Tholen, D.J., Buie, M.W. [1997]. Bulk properties of Pluto and Charon. In: Stern, S.A., Tholen, D.J. (Eds.), Pluto and Charon. The University of Arizona Press), we prefer the thermal gradient solution or a combination of haze and thermal gradient to explain the occultation light curves. (C) 2014 Elsevier Inc. All rights reserved.

•We map locations and compositions of volatiles at Loki Patera on Jupiter’s moon Io.•Those results constrain models of the Loki “periodic” resurfacing wave.•The light deposits in Loki Patera called “bergs” are composed primarily of sulfur.•The “bergs” avoid each other and avoid the patera margins.•Some “bergs” survive resurfacings and so are not just lava crust fumarolic deposits.

The width and temperature of the active fissures on Saturn's satellite Enceladus provide key observable constraints on physical models of these geyser-like eruptions. We analyze a sequence of high spatial resolution near-infrared spectra acquired with VIMS at 0.025 s intervals during a 74 km altitude flyover of the South Pole of Enceladus by the Cassini spacecraft on 14 April 2012 UTC. A thermal-emission spectrum covering 3- to 5-mu m wavelengths was detected as the field of view crossed one of the four major fissures, Baghdad Sulcus, within I km of 82.36S latitude and 28.24W longitude. We interpret this spectrum as thermal emission from a linear fissure with temperature 197 +/- 20 K and width 9 m. At the above wavelengths, the spectrum is dominated by the warmest temperature component. Looking downward into the fissure at only 13 degrees from the vertical, we conclude that our results measure the temperature of the interior fissure walls (and the H2O vapor) at depths within 40 m of the surface. (C) 2013 Elsevier Inc. All rights reserved.

The Pele region of lo has been the site of vigorous volcanic activity from the time of the first Voyager 1 observations in 1979 up through the final Galileo ones in 2001. There is high-temperature thermal emission from a visibly dark area that is thought to be a rapidly overturning lava lake, and is also the source of a large sulfur-rich plume. We present a new analysis of Voyager I visible wavelength images, and Galileo Solid State Imager (SSI) and Near Infrared Mapping Spectrometer (NIMS) thermal emission observations which better define the morphology of the region and the intensity of the emission. The observations show remarkable correlations between the locations of the emission and the features seen in the Voyager images, which provide insight into eruption mechanisms and constrain the longevity of the activity. We also analyze an additional wavelength channel of NIMS data (1.87 mu m) which paradoxically, because of reduced sensitivity, allows us to estimate temperatures at the peak locations of emission. Measurements of eruption temperatures on lo are crucial because they provide our best clues to the composition of the magma. High color temperatures indicative of ultramafic composition have been reported for the Pillan hot spot and possibly for Pele, although recent work has called into question the requirement for magma temperatures above those expected for ordinary basalts. Our new analysis of the Pele emission near the peak of the hot spot shows color temperatures near the upper end of the basalt range during the 127 and 132 encounters. In order to analyze the observed color temperatures we also present an analytical model for the thermal emission from fire-fountains, which should prove generally useful for analyzing similar data. This is a modification of the lava flow emission model presented in Howell (Howell, R.R. [1997]. Icarus 127, 394-407), adapted to the fire-fountain cooling curves first discussed in Keszthelyi et al. (Keszthelyi, L., Jaeger, W., Milazzo, M., Radebaugh, J., Davies, A.G., Mitchell, K.L. [2007]. Icarus 192, 491-502). When applied to the 132 observations we obtain a fire-fountain mass eruption rate of 5.1 x 10(5) kg s(-1) for the main vent area and 1.4 x 10(4) kg s(-1) for each of two smaller vent regions to the west. These fire-fountain rates suggest a solution to the puzzling lack of extensive lava flows in the Pele region. Much of the erupted lava may be ejected at high speed into the fire-fountains and plumes, creating dispersed pyroclastic deposits rather than flows. We compare gas and silicate mass eruption rates and discuss briefly the dynamics of this ejection model and the observational evidence. (C) 2011 Elsevier Inc. All rights reserved.