Hot spots on Io: Initial results from Galileo's near infrared mapping spectrometerLopes‐Gautier, Rosaly; Davies, A. G.; Carlson, R.; Smythe, W.; Kamp, L.; Soderblom, L.; Leader, F. E.; Mehlman, R.
doi: 10.1029/97GL02662pmid: N/A
The Near‐Infrared Mapping Spectrometer on Galileo has monitored the volcanic activity on Io since June 28, 1996. This paper presents preliminary analysis of NIMS thermal data for the first four orbits of the Galileo mission. NIMS has detected 18 new hot spots and 12 others which were previously known to be active. The distribution of the hot spots on Io's surface may not be random, as hot spots surround the two bright, SO2‐rich regions of Bosphorus Regio and Colchis Regio. Most hot spots seem to be persistently active from orbit to orbit and 10 of those detected were active in 1979 during the Voyager encounters. We report the distribution of hot spot temperatures and find that they are consistent with silicate volcanism.
High‐temperature hot spots on Io as Seen by the Galileo solid state imaging (SSI) ExperimentMcEwen, Alfred S.; Simonelli, Damon P.; Senske, David R.; Klaasen, Kenneth P.; Keszthelyi, Laszlo; Johnson, Torrence V.; Geissler, Paul E.; Carr, Michael H.; Belton, Michael J. S.
doi: 10.1029/97GL01956pmid: N/A
High‐temperature hot spots on Io have been imaged at ∼50 km spatial resolution by Galileo's CCD imaging system (SSI). Images were acquired during eclipses (Io in Jupiter's shadow) via the SSI clear filter (∼0.4–1.0 µm), detecting emissions from both small intense hot spots and diffuse extended glows associated with Io‧s atmosphere and plumes. A total of 13 hot spots have been detected over ∼70% of Io–s surface. Each hot spot falls precisely on a low‐albedo feature corresponding to a caldera floor and/or lava flow. The hot‐spot temperatures must exceed ∼700 K for detection by SSI. Observations at wavelengths longer than those available to SSI require that most of these hot spots actually have significantly higher temperatures (∼1000 K or higher) and cover small areas. The high‐temperature hot spots probably mark the locations of active silicate volcanism, supporting suggestions that the eruption and near‐surface movement of silicate magma drives the heat flow and volcanic activity of Io.
Temperature and area constraints of the South Volund Volcano on Io from the NIMS and SSI instruments during the Galileo G1 orbitDavies, Ashley Gerald; McEwen, Alfred S.; Lopes‐Gautier, Rosaly M. C.; Keszthelyi, Laszlo; Carlson, Robert W.; Smythe, William D.
doi: 10.1029/97GL02310pmid: N/A
Analysis of data from darkside and eclipse observations of Io by the NIMS and SSI instruments show that the South Volund hot spot is a manifestation of high temperature active silicate volcanism. The NIMS data are fitted with a two temperature model (developed from modelling terrestrial lavas) which yields a better fit to the data than a single temperature fit. The multispectral color temperatures obtained from NIMS are compared with the brightness temperatures obtained from the SSI instrument, and show excellent agreement for the hotter of the two components fitted to the NIMS data. The two components might correspond to a cooled crust which has formed on the surface of an active flow or lava lake, at a temperature of approximately 450 K, and covering an area of about 50 km², and a hotter and much smaller component, at a temperature of approximately 1100 K and an area of less than 0.1 km². The hot component implies the existence of cracks in the surface crust of a flow or lake through which the hot interior radiates, a hot vent area, or breakouts of lava forming new flow lobes. The ratio of these areas is consistent with the crack‐to‐crust ratio of some lava flows and lava lakes on Earth.
A history of high‐temperature Io volcanism: February 1995 to May 1997Spencer, John R.; Stansberry, John A.; Dumas, Christophe; Vakil, David; Pregler, Randy; Hicks, Michael; Hege, Keith
doi: 10.1029/97GL02591pmid: N/A
Ground‐based observations of Io's infrared thermal emission between February 1995 and May 1997 show several discrete brightenings for which we can constrain locations, fluxes, and durations. Several of these were brief high‐temperature events, with temperatures up to at least 1500 K, similar to but often smaller than the rare “outbursts” seen previously. Loki, Io's most powerful volcano, was relatively active before and probably during Galileo's December 1995 Io flyby, was faint during most of 1996, and began a major, long‐lived brightening between February 20 and March 12 1997. Thermal emission was not seen from Ra Patera, site of an active plume in Galileo images. Major outbursts were seen on March 2nd and September 27 1995.
Io's thermal anomalies: Clues to their origins from comparison of ground based observations between 1 and 20 µmBlaney, Diana L.; Veeder, Glenn J.; Matson, Dennis L.; Johnson, Torrence V.; Goguen, Jay D.; Spencer, John R.
doi: 10.1029/97GL02509pmid: N/A
Io's thermal emission for 1995 from eclipse photometry at 2.2 µm; broad band radiometry at 4.8 µm 8.7 µm and 20 µm; and in eclipse imaging between 1.7 and 5 µm are compared. The variability of thermal emission from Io at wavelengths between 1–5 µm (Silverstone et al., 1995; Spencer et al., 1997) is in agreement with the expected variability based on the 13 year record presented in Veeder et al. (1994) and Goguen et al. (1996). We conclude that 1995 was typical for Io, in terms of overall observed variability in the volcanic sources. Detailed comparison of data from Goguen et al. on Aug. 24 and Spencer et al. on Aug. 26 provides evidence of a high temperature eruption that produced a larger, cooler region over the course of two days. The observed frequency of occurrence of high temperature events, the linking of high and lower temperature thermal anomalies, and the observed stability of volcanic regions since Voyager suggests that high temperature silicate eruptions could support the entire observed population of cooler temperature anomalies. It may be more productive to consider sulfur flows on Io in the context of remobilization of existing sulfur deposits.
Thermal models for basaltic volcanism on IoKeszthelyi, L.; McEwen, A.
doi: 10.1029/97GL01368pmid: N/A
We present a new model for the thermal emissions from active basaltic eruptions on Io. While our methodology shares many similarities with previous work, it is significantly different in that (1) it uses a field tested cooling model and (2) the model is more applicable to pahoehoe flows and lava lakes than fountain‐fed, channelized, 'a'a flows. This model demonstrates the large effect lava porosity has on the surface cooling rate (with denser flows cooling more slowly) and provides a preliminary tool for examining some of the hot spots on Io. The model infrared signature of a basaltic eruption is largely controlled by a single parameter, τ, the average survival time for a lava surface. During an active eruption surfaces are quickly covered or otherwise destroyed and typical values of τ for a basaltic eruption are expected to be on the order of 10 seconds to 10 minutes. Our model suggests that the Galileo SSI eclipse data are consistent with moderately active to quiescent basaltic lava lakes but are not diagnostic of such activity.
Geology and topography of Ra Patera, Io, in the Voyager era: Prelude to eruptionSchenk, Paul M.; McEwen, Alfred; Davies, A. G.; Davenport, Trevor; Jones, Kevin; Fessler, Brain
doi: 10.1029/97GL02688pmid: N/A
Voyager era stereo images are used to map the geology and topography of Ra Patera (a major active volcanic center and possible site of sulfur eruptions on Io). The summit of Ra Patera reaches only ∼1 km above the surrounding plains. Pre‐Voyager‐era lava flows occur on slopes of 0.1–0.3°, comparable to the lunar mare. These flows were emplaced at either low viscosities, high eruption rates, or both. A 600‐km‐long ridged mountain unit (rising to ∼8 km near Carancho Patera) forms a 60 by 90 km wide plateau ∼0.5 km high 50 km east of Ra Patera. The new lava flows observed by Galileo flowed around the southern edge of this plateau.
The Pele Plume (Io): Observations with the Hubble Space TelescopeSpencer, John R.; Sartoretti, Paola; Ballester, Gilda E.; McEwen, Alfred S.; Clarke, John T.; McGrath, Melissa A.
doi: 10.1029/97GL02592pmid: N/A
In July 1996, with the Hubble Space Telescope (HST), we observed the Pele plume silhouetted against Jupiter at a wavelength of 0.27µm, the first definitive observation of an Io plume from Earth. The height, 420 ± 40 km, was greater than any plume observed by Voyager. The plume had significantly smaller optical depth at 0.34 and 0.41µm, where it was not detected. The wavelength dependence of the optical depth can be matched by a plume either of fine dust, with minimum mass of 1.2 × 109 g and maximum particle size of 0.08µm, or of SO2 gas with a column density of 3.7 × 1017 cm−2 and total mass of 1.1 × 1011 g. Our models suggest that early Voyager imaging estimates of the minimum mass of the Loki plume (Collins, 1981) may have been too large by a factor of ∼ 100. We may have detected the Pele plume in reflected sunlight, at 0.27µm, in July 1995, but did not see it 21 hours earlier, so the plume may be capable of rapid changes.
Io: Galileo evidence for major variations in regolith propertiesSimonelli, Damon P.; Veverka, Joseph; McEwen, Alfred S.
doi: 10.1029/97GL02506pmid: N/A
Galileo SSI images taken at different times early in the Jupiter orbital tour show striking, widespread changes in Io's color and albedo patterns that result from observing the satellite's surface at different lighting and viewing geometries. Such changes indicate significant variations in the photometric or light‐scattering behavior of the Ionian surface from region to region, and thereby provide strong evidence for major lateral variations in regolith properties. In particular, the regolith particles in Io's bright equatorial band appear to be larger than, or have a higher density of internal scatterers than, those in the satellite's higher‐latitude regions. Such heterogeneity is not surprising on Io, given the rapid rate of volcanic resurfacing.