Eruption Plumes of Io

Extraterrestrial volcanism and imagery analysis

Welcome to Io

Astronomers use imagery as a fundamental tool for observing the

Universe. All modern telescopes and spacecraft are equipped with

instrumentation which collects stores and transmits imagery in digital

form. This digital imagery can then be enhanced to aid astronomers

in observing specific phenomena. Upon successful completion of this lab,

students will achieved the following outcomes:

• Learn the fundamental physical nature of the Galilean moon Io through active manipulation of imagery;
• Learn the power and flexibility of digital imagery analysis
• Critically analyze imagery in order to infer the nature of volcanism on Io
• Integrate mathematics into imagery analysis in order to extract additional insights
• Communicate and interact with group members in order to reach a maximum variety of perspectives and potential solutions

Begin

You and your group will need a computer workstation with both the software package Image J and the associated Io images loaded. Your instructor will assist you.

a Open the Io image. Do this by going to File and selecting Open. DOUBLE-CLICKING ON THE IMAGE WILL OPEN DIFFERENT SOFTWARE. DON’T DO THIS.

Io is the innermost Galilean satellite of Jupiter. It is slightly larger than

Earth’s Moon. The densities of the Moon and Io are nearly the same,

indicating that they are both made of rocky material. However, the Moon

is geologically “dead”, while Io is the most volcanically active body in the

Solar System.

Io is caught in a gravitational tug-of-war between Jupiter and its other

moons. As Io orbits Jupiter, its distance from the planet changes. Io is

flexed (stretched) in different directions by the changing tidal forces.

The friction created by this flexing produces enough heat to keep parts

of Io’s interior molten.

At first, the Voyager scientists processed images of Io to bring out

surface detail. They were delighted to discover volcanic cones and flows.

These signs of recent volcanic activity made headlines around the world.

1. Describe any evidence of active volcanism you see on the surface.

a Open the Prometheus image.

One of the images showed a large, unexpected bubble-like feature above

Io’s surface. Further examination revealed that the cameras had caught

a volcano in the act of erupting. In all, scientists discovered nine active

volcanoes on Io. In this activity, you’ll measure and study these plumes.

a Adjust the brightness and the contrast of the image to show the surface

features as clearly as possible.

a Experiment with different color tables to see which one best shows

the structure of the plume. Experiment with other features of the software. See what it can do.

Based on the camera’s distance from Io, scientists know that the width

of each pixel in the image represents a distance of 4.16 km. This scale has

been set for you.

a Use the line tool combined with analyze/measure to measure the maximum height of the plume (named Prometheus). Magnifying the plume using the magnification tool will make it easier to measure.

2. Record the height you measured for Prometheus.

3. Use the plume height you measured to calculate the ejection velocity of the

material that forms Prometheus. (Remember to convert to meters!)

The equation for ejection velocity is:

Where

v = ejection velocity in m/sec

g = surface gravity in m/sec²

h = plume height in m

The average surface gravity for Io is 1.79 m/sec²

4. Prometheus is actually 5° in front of Io’s limb instead of right on the

edge. Would the actual height of the plume be greater than or less

than your measured height? Why?

5. The true height of Prometheus, corrected for limb geometry, is 77 km.

Calculate the ejection velocity again, using the actual height.

6. Commercial jets fly at about 500 miles per hour. Compare this value to the

ejection velocity of the plume material. (Convert units as necessary. 1 mile = 1.585 km.)

Pele

a Open the Pele image.

This image of Io was taken through an ultraviolet filter. It shows Pele, the

largest volcanic plume observed on Io.

a Enhance the image to discover the plume for yourself. Experiment with the

contrast and/or color tables to get the best view of the entire plume.

7. The scale of this image has been set to 7.5 km/pixel. Measure the height of

Pele and determine the ejection velocity of the volcanic material for this

plume.

8. Measure the width of the plume and calculate the total area covered by the

fallout from the plume (assume the plume fallout is circular in shape).

The area of a circle = πR²

Loki

a Open Loki 1. This is another eruption area, viewed from above.

a Adjust the brightness and contrast for the clearest view of the area.

Loki is the site of a fissure eruption on Io. It is a long, straight eruption

vent with plumes at each end. The fan-shaped, hazy, dark material on the

left end of the fissure is Plume 2. Plume 9 is the smaller, less obvious

dark area at the right end. Below the fissure, the dark horseshoe-shaped

feature is possibly a lake of molten sulfur with solid “sulfurbergs”

floating in it.

a Open Loki 2 and Loki 3.

These images show Loki’s plumes from another angle, above Io’s limb.

Voyager 1 took Loki 2 in March 1979. Loki 3 was taken about 4 months

later by Voyager 2. The viewing angle and scale are not the same for each

image.

a Scale and rotate the images to the same size and orientation so that you can

compare them more easily.

a Adjust the brightness and contrast of both images to view and compare the

plumes, seen above Io’s limb.

9. Describe any changes in the size of each plume between the two Voyager

encounters.

10. Do you think these changes are due to differences in ejection velocity or

changes in the amount of material erupted? Why?

Conclusions

Write a 2-3 paragraph conclusion detailing what was learned about Io through the image processing techniques, being certain to explain how those techniques assisted in analysis of the images.