Elsevier

Icarus

Volume 179, Issue 1, 1 December 2005, Pages 235-251
Icarus

Volcanic activity at Tvashtar Catena, Io

https://doi.org/10.1016/j.icarus.2005.05.013Get rights and content

Abstract

Galileo's Solid State Imager (SSI) observed Tvashtar Catena four times between November 1999 and October 2001, providing a unique look at a distinctive high latitude volcanic complex on Io. The first observation (orbit I25, November 1999) resolved, for the first time, an active extraterrestrial fissure eruption; the brightness temperature was at least 1300 K. The second observation (orbit I27, February 2000) showed a large (500km2) region with many, small, hot, regions of active lava. The third observation was taken in conjunction with Cassini imaging in December 2000 and showed a Pele-like, annular plume deposit. The Cassini images revealed an 400km high Pele-type plume above Tvashtar Catena. The final Galileo SSI observation of Tvashtar (orbit I32, October 2001), revealed that obvious (to SSI) activity had ceased, although data from Galileo's Near Infrared Mapping Spectrometer (NIMS) indicated that there was still significant thermal emission from the Tvashtar region. In this paper, we primarily analyze the style of eruption during orbit I27 (February 2000). Comparison with a lava flow cooling model indicates that the behavior of the Tvashtar eruption during I27 does not match that of simple advancing lava flows. Instead, it may be an active lava lake or a complex set of lava flows with episodic, overlapping eruptions. The highest reliable color temperature is 1300K. Although higher temperatures cannot be ruled out, they do not need to be invoked to fit the observed data. The total power output from the active lavas in February 2000 was at least 1011W.

Introduction

Jupiter's moon, Io (Fig. 1), the most volcanically active body in the Solar System, has provided important insight into volcanic processes on the terrestrial planets. The nature of Io's volcanic activity has been the subject of intense investigation since its discovery in 1979 (e.g., Witteborn et al., 1979, Morabito et al., 1979). Peale et al. (1979) predicted the existence of volcanism caused by tidally induced heating. Io is deformed into triaxial ellipsoids of changing dimensions due to its eccentric orbit around Jupiter, forced by orbital resonances with Europa and Ganymede (e.g., Greenberg, 1982). This tidal flexing causes about two orders of magnitude more heating than any plausible non-tidal mechanism (Peale et al., 1979). This prodigious amount of energy heats Io's interior, is transported via volcanism to the surface, and is eventually lost to space. Io's power output is on the order of 1014 W (cf. Matson et al., 1981, Veeder et al., 2004).

The Voyager spacecraft discovered 22 active hotspots Pearl and Sinton, 1982, McEwen et al., 1992a, McEwen et al., 1992b. Nine active eruptive plumes were detected Strom et al., 1981, McEwen et al., 1989. The composition of the lavas was not established by Voyager, and is still unclear today. The colors and temperature constraints on the lavas as observed by Voyager and ground-based instruments were all consistent with sulfurous lava compositions. Voyager's Infrared Interferometer Spectrometer and Radiometer (IRIS) did not have sufficient signal at short wavelengths to show the existence of high temperatures that would indicate silicate lavas. Many of the investigators of the era thought that the surface expression of Io's volcanoes was dominated by sulfurous rather than silicate lavas. However, later, ground-based, telescopic observations of infrared emissions from Io revealed temperatures in excess of the boiling point of sulfur (718 K) or likely sulfur compounds Johnson et al., 1988, Veeder et al., 1994. By the time Galileo arrived in Jupiter orbit, it had been predicted that active silicate (i.e., basaltic) and sulfur volcanism would be seen on Io's surface (e.g., Blaney et al., 1995, Spencer and Schneider, 1996). When Galileo returned thermal information about Io's volcanoes, most exhibited temperatures consistent with basaltic lavas (1200–1400 K) although even higher temperatures could not be ruled out (e.g., McEwen et al., 1998a, Davies et al., 2000b). At least one of the volcanoes exhibited temperatures too high to be explained by normal basaltic lavas. A 1997 eruption of Pillan patera was observed to have a minimum temperature of 1870 K estimated through model fits to NIMS spectra and SSI color images of the thermal emission McEwen et al., 1998b, Davies et al., 2001.

The goals of the present study are: (1) to provide a reliable temperature estimate for the liquid lava temperatures during the eruptions at Tvashtar that were observed by Galileo SSI, (2) to provide improved error analysis techniques for further study of SSI observations of other active volcanoes on Io, and (3) to discuss application of, and modifications to, existing lava flow cooling models to Tvashtar and other volcanoes.

The Galileo spacecraft spent a very productive eight years in orbit of the jovian system, completing 34 orbits during its mission. Galileo entered Jupiter orbit in December 1995, and ended its tour by diving into Jupiter's atmosphere in September 2003. High spatial resolution imaging of the innermost Galilean satellite, Io, was abandoned during Jupiter Orbit Insertion (JOI) due to a concern about the condition of the tape recorder, and was subsequently postponed until late in the first mission extension because of the high-energy radiation environment close to Jupiter. Unfortunately, during the final orbits, the effects of age and the intense radiation environment took their toll on the spacecraft and camera, resulting in the loss of roughly half of the Io imaging observations during the extended missions McEwen et al., 2000, Keszthelyi et al., 2001, Turtle et al., 2001, Turtle et al., 2004. Despite these problems, Galileo returned an extremely valuable scientific data set, including data from other remote sensing instruments such as NIMS (e.g., Lopes et al., 2004, Lopes et al., 2001, and references therein) and the Photo-Polarimeter Radiometer (PPR) (e.g., Rathbun et al., 2004).

Galileo had highly elliptical orbits around Jupiter, so data collection was concentrated around perijove. Each orbit had a targeted close flyby of one of the Galilean satellites. Orbits were named according to the first letter of the targeted satellite and the orbit number. For example, the seventh jovian orbit, during which Ganymede was the satellite to which Galileo made its closest approach, was called G7.

Section snippets

Styles of volcanism on Io

The surface manifestation of Io's tidal heating is its volcanoes, whose eruptions are quite varied, from gaseous plumes reaching hundreds of kilometers above the surface to different types of flow fields and lava lakes. Each of these styles of volcanism provides us with clues to the nature of Io's interior and its geologic history.

The Galileo Solid State Imager

The Solid State Imaging (SSI) camera on Galileo used an 800×800 pixel charge coupled device (CCD) as its detector, with a filter wheel containing eight filters Klaasen et al., 1997, Klaasen et al., 1999, Klaasen et al., 2003. The filters used for collecting data at Io were the 413 nm (violet), 559 nm (green), 664 nm (red), 756 nm, and 889 nm bandpass filters, a 968 nm cutoff (>968nm) filter, and a clear filter (380–1100 nm) (Turtle et al., 2004). The clear filter's effective center wavelength

Observations of volcanic activity at Tvashtar

Tvashtar Catena (63° N, 120° W) (Fig. 1) is a chain of large paterae that has exhibited highly variable volcanic activity over the Galileo mission. Tvashtar was first imaged in global views by the Voyager spacecraft (Fig. 3). Its gross structure was essentially unchanged from the Voyager to Galileo eras. Evidence for a hotspot at Tvashtar was first detected in an eclipse observation in April 1997 (Orbit G7) by Galileo SSI (McEwen et al., 1998a). No further activity was detected until August

Liquid lava temperatures

The most reliable temperature estimates for the I25 (brightness temperature) and I27 (color temperature) eruptions are near 1300 K. For a color temperature of 1300 K, we can only estimate the actual liquid lava temperature by assuming an exposure age (Fig. 11). An eruption temperature of 1500 K (basaltic composition) would suggest an exposure age τ=10s for the entire active surface of the I27 eruptive region. A 1700 K (ultramafic composition) temperature of the liquid would imply τ=100s.

Acknowledgements

The authors thank David Williams and Rosaly Lopes for thorough and insightful reviews from which this manuscript benefited greatly. We would also like to thank the Galileo SSI team for their hard work and dedication in acquiring the rich data set without which this work would not have been possible.

References (69)

  • F. Marchis et al.

    Keck AO survey of Io global volcanic activity between 2 and 5 μm

    Icarus

    (2005)
  • A.S. McEwen et al.

    Two classes of volcanic plumes on Io

    Icarus

    (1983)
  • A.S. McEwen et al.

    Active volcanism on Io as seen by Galileo SSI

    Icarus

    (1998)
  • J. Radebaugh et al.

    Observations and temperatures of Io's Pele patera from Cassini and Galileo spacecraft images

    Icarus

    (2004)
  • J.A. Rathbun et al.

    Mapping of Io's thermal radiation by the Galileo photopolarimeter-radiometer (PPR) instrument

    Icarus

    (2004)
  • G.J. Veeder et al.

    The polar contribution to the heat flow of Io

    Icarus

    (2004)
  • D. Blaney et al.

    Io's thermal anomalies: Clues to their origins from comparison of ground-based observations between 1 and 20 μm

    Geophys. Res. Lett.

    (1995)
  • P. Burgi et al.

    Field temperature measurements at Erta'Ale Lava Lake, Ethiopia

    Bull. Volcanol.

    (2002)
  • A.G. Davies

    Temperature, age and crust thickness distributions of Loki patera on Io from Galileo NIMS data: Implications for resurfacing mechanism

    Geophys. Res. Lett.

    (2003)
  • A.G. Davies

    Volcanism on Io: Estimation of eruption parameters from Galileo NIMS data

    J. Geophys. Res.

    (2003)
  • A.G. Davies et al.

    Eruption evolution of major volcanoes on Io: Galileo takes a close look

    Lunar Planet. Sci.

    (2000)
  • A.G. Davies et al.

    Thermal signature, eruption style, and eruption evolution at Pele and Pillan on Io

    J. Geophys. Res.

    (2001)
  • A.G. Davies et al.

    ‘Active’ and ‘passive’ lava resurfacing processes on Io: A comparative study of Loki patera and Prometheus

    Lunar Planet. Sci.

    (2004)
  • L.A. Frank et al.

    Passage through Io's ionospheric plasmas by the Galileo spacecraft

    J. Geophys. Res.

    (2001)
  • P.E. Geissler et al.

    Morphology and time variability of Io's visible aurora

    J. Geophys. Res.

    (2001)
  • R. Greenberg

    Orbital evolution of the Galilean satellites

  • A.J.L. Harris et al.

    Mass flux measurements at active lava lakes: Implications for magma recycling

    J. Geophys. Res.

    (1999)
  • R.W. Hopper et al.

    Thermal histories and crystal distributions in partly devitrified lunar glasses cooled by radiation

    Proc. Lunar Sci. Conf.

    (1974)
  • R.R. Howell et al.

    Ground-based observations of volcanism on Io in 1999 and early 2000

    J. Geophys. Res.

    (2001)
  • T.V. Johnson et al.

    Io: Evidence for silicate volcanism in 1986

    Science

    (1988)
  • T.V. Johnson et al.

    Stealth plumes on Io

    Geophys. Res. Lett.

    (1995)
  • L. Keszthelyi et al.

    The initial cooling of pahoehoe flow lobes

    Bull. Volcanol.

    (1996)
  • L. Keszthelyi et al.

    Thermal models for basaltic volcanism on Io

    Geophys. Res. Lett.

    (1997)
  • L. Keszthelyi et al.

    Imaging of volcanic activity on Jupiter's moon Io by Galileo during the Galileo Europa mission and the Galileo Millennium mission

    J. Geophys. Res.

    (2001)
  • Cited by (33)

    • Variations in the canopy shock structures of massive extraterrestrial plumes: Parametric DSMC simulation of 2007 Tvashtar observations

      2021, Icarus
      Citation Excerpt :

      This location coincides with the November 1999 fire fountains seen by Galileo at Tvashtar. A blackbody fit provides a lower limit to the magma temperature of 1287 K, comparable to Galileo estimates by Milazzo et al. (2005) (and Rathbun et al., 2014 for Tvashtar). The temperatures are consistent with basaltic lava composition and an energetic eruption such as a fire fountain, as opposed to lava flows.

    • Hybrid dust-tracking method for modeling Io's Tvashtar volcanic plume

      2021, Icarus
      Citation Excerpt :

      The source may be composed of any number of surface features such as long fissures or millions of small, millimeter-sized holes. During the Galileo observations, these sources were likely flowing surface lavas and fire fountains (McEwen et al., 1998; Millazzo et al., 2005). While Galileo came within 200 km of Io's surface during its mission, New Horizons was never closer than 2000,000 km from the surface.

    • Time variability of Io's volcanic activity from near-IR adaptive optics observations on 100 nights in 2013–2015

      2016, Icarus
      Citation Excerpt :

      While we detected thermal emission from both sites during our program, P197 stayed active at a moderate level of activity for over a year, while Surt was barely detected twice, and only at 4.7 µm. We also detected no activity at Tvashtar Paterae, which has exhibited bright outbursts in the past (Howell et al., 2001; Milazzo et al., 2005), and was the most powerful event observed in 2006–2007, detected from the ground and by New Horizons (Laver et al., 2007; Rathbun et al., 2014; Spencer et al., 2007). Other sites that have exhibited past bright eruptions include Kanehekili Fluctus and Pillan Patera (detected from the ground: de Pater et al., 2016a; Marchis et al., 2002; de Pater et al., 2014a), and by Galileo: (Davies et al., 2001; Keszthelyi et al., 2001), which were all at or below our detection threshold in 2013–2015, until the eruption at Pillan Patera in Feb 2015 (de Pater et al., 2016a).

    View all citing articles on Scopus
    View full text