ECE Researchers Devise Method to See Invisible Planetary Gases

This image shows two distinct regions of sodium escaping from Io, with color-coded brightness levels are in arbitrary units.  The irregularly-shaped dark region denotes areas where the bright light from Io was too strong to allow the faint sodium emission to be seen.  The orientation key gives the sky-view from Earth.
This image shows two distinct regions of sodium escaping from Io, with color-coded brightness levels are in arbitrary units. The irregularly-shaped dark region denotes areas where the bright light from Io was too strong to allow the faint sodium emission to be seen. The orientation key gives the sky-view from Earth.

A group of Boston University researchers, led by Professor Michael Mendillo (CAS, ECE), have published the first clear evidence of how volcanic gases from Io, a moon of the planet Jupiter, can produce the largest visible gas cloud in the solar system.  The findings, published in the July 19th issue of the journal Nature, are the result of a signal processing technique devised by co-author Sophie Laurent (ECE ’04) that used high-definition imaging to combine several images of Io into one clear picture.

The research, funded by the National Science Foundation and the Air Force Office of Scientific Research, was a seven-year collaboration between the College of Engineering and Boston University Center for Space Physics.  In addition to Mendillo and Laurent, an ECE doctoral candidate working on her dissertation at the time, ECE professors Janusz Konrad and W.  Clem Karl also contributed heavily to the research.

“There’s never been one planetary science project in the Center for Space Physics that has been so overwhelmingly related to engineering than this project,” Mendillo said.  “The center of involvement during the image processing project was in the College of Engineering.”

The most active area for volcanic activity known anywhere, Io produces escaping gases that, if seen by the naked eye, would be the largest permanently visible object in the solar system.  But the combination of turbulence in the atmosphere and the faint visual of the gas when viewed from earth made it nearly impossible to view.

“Those were the two main problems,” Mendillo said.  “But our technique was to record digital images at video rates of one-sixtieth per second.  By taking very short exposures, the atmosphere may be steady for an instant and occasional sharp images might be found.”

The observations were taken in 2000 using a 4-meter class telescope operated by the U.S. Air Force on Maui, Hawaii.  The telescope recorded 62,500 images in an hour.

“Over the course of an hour, we were able to take enough data where some terrific images had to be there, but still not bright enough to publish or see,” he said.  “That’s where signal processing came into play.”

Under the guidance of Konrad and Karl, Laurent was able to find an automated method of searching the database of images, finding the best ones and combining and centering them into one central image.  The data not only revealed two distinct sources of sodium (Na) escaping from Io, but also the locations from which they escaped.

“So much of this project was signal processing,” Mendillo said.  “It was an innovative use of a relatively standard signal processing method applied to a completely different environment.  Sophie found the most consistent way to find the best images.”

The results, Mendillo said, were a true mixture of engineering techniques, optical instrumentation and scientific interpretation.

“It’s very unusual for an engineering breakthrough to be Nature,” he said.  “The journal liked the unusual way that Sophie devised to make her image as well as the signal processing aspect.  Applying signal processing to an astronomical object not only sharpened it, but it led to new results in planetary science on a spatial scale not possible before.”

This schematic (not to scale) shows the Earth-based view of the orbital configuration of Jupiter, Io, and the two distinct emission regions presented in Figure 1.  The symmetrical region from atmospheric sputtering is indicated for all orbital positions, together with the stream source confined to the direction of torus plasma flow past Io.
This schematic (not to scale) shows the Earth-based view of the orbital configuration of Jupiter, Io, and the two distinct emission regions presented in Figure 1. The symmetrical region from atmospheric sputtering is indicated for all orbital positions, together with the stream source confined to the direction of torus plasma flow past Io.