Sulfur dioxide and Sulfur in Tvashtar's Plume

There is a nice blog post by Ted Stryk, guest blogging for the Planetary Society at the Lunar and Planetary Sciences Conference, on some of the presentations from last night's poster sessions and yesterday afternoon's lunar session. One of posters Ted highlights is the one by Kandis Lea Jessup and John Spencer titled, "Detailed Analysis of the Tvashtar Plume Spectral Behavior." I highlighted the abstract for this poster last week.

Ted reports that the authors have determined that the S₂ to SO₂ ratio in the Tvashtar plume was between 0.01 and 0.02. In other words, in their measurements based on images taken by Hubble last February, the plume consisted of significantly more Sulfur dioxide than diatomic Sulfur. This value would seem to be in conflict with the presence of a red ring plume deposit, which is thought to be caused by the deposition of sulfur from Io's plumes. However, measurements of the Pele plume suggest that the Sulfur to Sulfur dioxide in these larger plumes can vary between 0.01 and 0.3, so the low ratio at Tvashtar may not be representative of the average.

Another consequence of the low S₂/SO₂ ratio is that the high optical depth seen in the Hubble WFPC2's F255W filter (an ultraviolet filter that senses gases in Io's plumes, rather than the dust seen in visible wavelength images like the LORRI images above) was not due to absorption by S₂, but instead is due to SO₂.

An interesting result. Definitely indicates that Tvashtar's plume was quite gas rich.

LPSC 2008: Detailed Analysis of the Tvashtar Plume Spectral Behavior

In the second LPSC abstract highlighted on this blog, Kandis Lea Jessup and John Spencer present the work they have done on Hubble images of Io taken during last year's New Horizons encounter. In particular, they are using the images they acquired at different wavelengths with Hubble's Wide Field and Planetary Camera 2 to study the spectral behavior of the Tvashtar plume.

While the images acquired by Hubble have a lower spatial resolution than those taken by New Horizons' LORRI camera (180 km per pixel for the WFPC2 versus at top resolution of 11.2 km per pixel for LORRI), the WFPC2 has a higher spectral resolution than New Horizons' MVIC instrument, particularly at ultraviolet wavelengths which is particularly important for identifying gases within Io's plumes. Jessup and Spencer observed Io and the Tvashtar plume on multiple occassions last February, allowing the authors to examine the plume's reflectance spectra (i.e. looking at how much light reflects off the plume, which can depend on composition, particle size, and phase angle) and absorption spectra (i.e. looking at how much light from the background Jupiter passes through the plume to Hubble).

The authors found the plume to be most noticeable in both sets of observation in the ultraviolet F255W filter, indicative of S2 gas in the plume. The authors had a similar result at Pele in 2000. They do note that the Tvashtar plume has a much higher optical depth in the F255W filter than Pele.

Interesting work. They do promise to present more work on how optical depth varies by wavelength for both Pele and Tvashtar in their poster. It is so interesting to see just how similar the Pele and Tvashtar plumes despite the apparent difference in volcanic styles: Pele being a vigorously erupting lava lake and Tvashtar being a fissure eruption. Must have to do with the magmas at both locations having a higher volatile content, allowing the formation of a bright lava fountain at Tvashtar and a constantly overturning lava lake at Pele. Note the fact that as far as I know, Pele and Tvashtar are the only two volcanoes where using relatively short exposures, it is easy to see their hotspots in the daylight, at wavelengths less than 1 micron, and at relatively low resolutions.

Link: Detailed Analysis of the Tvashtar Plume Spectral Behavior [www.lpi.usra.edu]