In turn, rocky-object astronomy is used to study Io.
Volcanic activity[edit | edit source]
"One of Jupiter’s moons has unleashed a series of huge volcanic eruptions [imaged at the top of the page] over a hellish 2 week period that were so bright they could be studied in detail by ground based observatories."
“We typically expect one huge outburst every one or two years, and they’re usually not this bright.”
“Here we had three extremely bright outbursts, which suggest that if we looked more frequently we might see many more of them on Io.”
“These new events are in a relatively rare class of eruptions on Io because of their size and astonishingly high thermal emission. The amount of energy being emitted by these eruptions implies lava fountains gushing out of fissures at a very large volume per second, forming lava flows that quickly spread over the surface of Io.”
"While recording the eruptions that occurred in the moon’s southern hemisphere on Aug. 15, 2013, the researchers saw the brightest emanate from a caldera called Rarog Patera, which produced a 50 square-mile, 30 foot-thick lava flow — enough lava to cover Manhattan Island. Another eruption that was generated by the caldera Heno Patera produced a flow covering 120 square miles. Both eruptions generated “curtains of fire” as lava blasted from long fissures in Io’s crust."
"Images [on the right are] of Io obtained at different infrared wavelengths (in microns, μm, or millionths of a meter) with the W. M. Keck Observatory’s 10-meter Keck II telescope on Aug. 15, 2013 (a-c) and the Gemini North telescope on Aug. 29, 2013 (d). The bar on the right of each image indicates the intensity of the infrared emission. Note that emissions from the large volcanic outbursts on Aug. 15 at Rarog and Heno Paterae have substantially faded by Aug. 29. A second bright spot is visible to the north of the Rarog and Heno eruptions in c and to the west of the outburst in d. This hot spot was identified as Loki Patera, a lava lake that appeared to be particularly active at the same time."
On the left is a five-image sequence of New Horizons images showing Io's volcano Tvashtar spewing material 330 km above its surface.
The pair of images on the right changes in surface features for the eight years between Galileo and New Horizons observations.
Theoretical volcanic Io[edit | edit source]
"Io is Jupiter’s innermost Galilean moon that is 2,300 miles wide, approximately the same size as our moon, and is the only place in the solar system (except Earth) where active volcanoes have been observed. The volcanic activity is driven by powerful tidal interactions with the gas giant that squeeze Io’s interior, heating it up. Like Earth’s volcanoes, molten rock (magma) is then forced through Io’s crust intermittently erupting as volcanoes."
"Io is the most volcanic body in the solar system, boasting activity 25 times that of Earth. Some of Io's volcanoes blast plumes of sulfur and other material 250 miles (400 kilometers) above the moon, which is completely resurfaced every million years or so. On Thursday (April 4), NASA released a video of Io's volcano plumes based on five images snapped by the agency's Pluto-bound New Horizons spacecraft in March 2007." One of these frames is on the right.
"The hundreds of volcanoes on Jupiter's moon Io aren't where they're supposed to be, [...] Io's major volcanic activity is concentrated 30 to 60 degrees farther east than models of its internal heat profile predict".
"The unexpected eastward offset of the volcano locations is a clue that something is missing in our understanding of Io. In a way, that's our most important result. Our understanding of tidal heat production and its relationship to surface volcanism is incomplete."
"This intense activity is ultimately generated by gravitational tugs from Jupiter, with an assist from the nearby moons Europa and Ganymede."
"Io completes two orbits for every one that Europa makes, and four for every one of Ganymede's laps. As a result of this regular timing, Europa and Ganymede have pulled the orbit of Io into an oval, with explosive consequences for the 2,260-mile-wide (3,640 km) moon."
"As Io moves closer to Jupiter, the planet's powerful gravity pulls hard on the moon, deforming it. This force decreases as Io retreats, and the moon bounces back. This cycle of flexing creates friction in Io's interior, which in turn generates enormous amounts of volcano-driving tidal heat."
"Common sense suggests that Io's volcanoes would be located above the spots with the most dramatic internal heating."
"What's causing the disconnect between expected and observed volcano locations remains a mystery. It's possible that Io is rotating faster than scientists think, researchers said. Or models of Io's tidal heating may be missing some components, such as the complications caused by an underground magma ocean."
"Our analysis supports a global subsurface magma ocean scenario as one possible explanation for the offset between predicted and observed volcano locations on Io. However, Io's magma ocean would not be like the oceans on Earth. Instead of being a completely fluid layer, Io's magma ocean would probably be more like a sponge with at least 20 percent silicate melt within a matrix of slowly deformable rock."
Volcanisms[edit | edit source]
"The view [on the right] includes two of Io's ten highest peaks, the Euboea Montes at upper extreme left and Haemus Mons at bottom." This mosaic of Voyager 1 images covers Io's south polar region. On the left is a mosaic of Voyager 1 images covering Io's south polar region. The view includes two of Io's ten highest peaks, the Euboea Montes at upper extreme left and Haemus Mons at bottom. Io "is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of 3,642 kilometres (2,263 mi), the fourth-largest moon in the Solar System. ... With over 400 active volcanoes, Io is the most geologically active object in the Solar System. ... Most of Io's surface is characterized by extensive plains coated with sulfur and sulfur dioxide frost. ... Io's volcanism is responsible for many of the satellite's unique features. Its volcanic plumes and lava flows produce large surface changes and paint the surface in various shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur."
In the image at right, "[t]he smallest features that can be discerned are 2.5 kilometers in size. There are rugged mountains several kilometers high, layered materials forming plateaus, and many irregular depressions called volcanic calderas. Several of the dark, flow-like features correspond to hot spots, and may be active lava flows. There are no landforms resembling impact craters, as the volcanism covers the surface with new deposits much more rapidly than the flux of comets and asteroids can create large impact craters. The picture is centered on the side of Io that always faces away from Jupiter; north is to the top."
"Color images acquired on September 7, 1996 have been merged with higher resolution images acquired on November 6, 1996 by the Solid State Imaging (CCD) system aboard NASA's Galileo spacecraft. The color is composed of data taken, at a range of 487,000 kilometers, in the near-infrared, green, and violet filters and has been enhanced to emphasize the extraordinary variations in color and brightness that characterize Io's face. The high resolution images were obtained at ranges which varied from 245,719 kilometers to 403,100 kilometers."
The second image at right is a "global view of Jupiter's moon, Io, ... obtained during the tenth orbit of Jupiter by NASA's Galileo spacecraft. Io, which is slightly larger than Earth's moon, is the most volcanically active body in the solar system. In this enhanced color composite, deposits of sulfur dioxide frost appear in white and grey hues while yellowish and brownish hues are probably due to other sulfurous materials. Bright red materials, such as the prominent ring surrounding Pele, and "black" spots with low brightness mark areas of recent volcanic activity and are usually associated with high temperatures and surface changes. One of the most dramatic changes is the appearance of a new dark spot (upper right edge of Pele), 400 kilometers (250 miles)in diameter which surrounds a volcanic center named Pillan Patera. The dark spot did not exist in images obtained 5 months earlier, but Galileo imaged a 120 kilometer (75 mile) high plume erupting from this location during its ninth orbit. North is to the top of the picture which was taken on September 19, 1997 at a range of more than 500,000 kilometers (310,000 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft."
The third image at right continues around Io to the left.
The fourth image is of Io's north pole. "[The] new basemap [and the polar images] of Jupiter's moon Io was produced by combining the best images from both the Voyager 1 and Galileo Missions. Although the subjovian hemisphere of Io was poorly seen by Galileo, superbly detailed Voyager 1 images cover longitudes from 240 W to 40 W and the nearby southern latitudes. A monochrome mosaic of the highest resolution images from both Galileo and Voyager 1 was assembled that includes 51 Voyager 1 images with spatial resolutions sometimes exceeding the 1 km/pixel scale of the final mosaic. Because this mosaic is made up of images taken at various local times of day, care must be taken to note the solar illumination direction when deciding whether topographic features display positive or negative relief. In general, the illumination is from the west over longitudes 40 to 270 W, and from the east over longitudes 270 W to 40 W. Color information was later superimposed from Galileo low phase angle violet, green, and near-infrared (756 nanometer wavelength) images. The Galileo SSI camera's silicon CCD was sensitive to longer wavelengths than the vidicon cameras of Voyager, so that distinctions between red and yellow hues can be more easily discerned. The "true" colors that would be visible to the eye are similar but much more muted than shown here. Image resolutions range from 1 to 10 km/pixel along the equator, with the poorest coverage centered on longitude 50 W."
The fifth image is of Io's south pole.
The last image is an animated image showing a 1 Io day of rotation. "In the same way that the Moon always has the same side facing Earth, Io always has the same side facing Jupiter. The movie shows two speeded-up rotations of Io (a single rotation really takes 1.77 days), and begins with a view of the Jupiter-facing hemisphere. With rotation in an easterly direction, after two seconds the volcano Prometheus (on the equator) comes into view. The massive red deposit around Pele (seconds 5-10) is the most distinctive expression of volcanic activity on Io, and just to the north-west is the horse shoe-shaped Loki Patera, the most powerful volcano on Io. The animation was made using a computer program that wrapped the Io mosaic around a sphere to produce a globe. In all, 360 images were used, each differing by one degree in longitude from the previous image."
Volcanic rocks[edit | edit source]
The surface of Io appears to be composed entirely of volcanic rocks as suggested by the image on the right.
Volcanology[edit | edit source]
"Voyager 1 IRIS [took] spectra of Io from 4- to 55 µm wavelength [...] A new model for Io's surface [...] includes 3 basic thermophysical units: (1) bright, SO2-rich regolith with a high thermal inertia over ~80 % of the surface; (2) darker, SO2-poor regolith with a low thermal inertia over ~18 % of Io; and (3) high-T hot spots over ~2 % of the surface. [...] unit 2 contains ubiquitous low-T geothermal anomalies from cooling volcanic deposits. [The] nighttime spectra [...] show a nearly constant T of 90 ± 5 K. Daytime Ts increase to about 120 K, with the peak Ts clearly occurring in the afternoon. [The estimated] minimum heat flow of Io from the power above background of the 25 most energetic and largely non-overlapping IRIS [field of view] FOVs [is] 2.9 x 1013W. [An extrapolated] global heat flow [gives] a total minimum power of 7.6 x 1013W, or 1.85 W m-2 as a global average heat flow. [...] We expect that the actual heat flow exceeds the theoretical upper limit to steady-state tidal heating, 9 x 1013W, as concluded previously [6, 14]."
"Nine previously unknown volcanoes have been discovered from this infrared image of Jupiter's moon Io, acquired by NASA's Galileo spacecraft on Oct. 16, 2001."
"The infrared image, on the right, serves as a thermal map to a section of Io's surface from pole to pole. An image from Galileo's camera showing the same face of Io (left) is included for correlating the heat-sensing infrared data with geological features apparent in visible wavelengths. The infrared image uses false color to portray the intensity with which the surface glows at the invisible wavelength of 5 microns, as observed by Galileo's near infrared mapping spectrometer instrument. White, reds and yellows indicate hotter regions; blues are cold. The resolution varies from 24 to 39 kilometers (15 to 24 miles) per picture element."
"Some of the hot spots visible in this image were not seen in a similar infrared image taken just 10 weeks earlier of an overlapping section of Io."
"Three sites of major activity in the images are Prometheus, which is a bright spot at center left; Amirani, which is an elongated feature in the upper right; and the site where a giant plume was erupting in August, which is the bright spot near the top of the image."
"Paterae, defined by the International Astronomical Union as irregular crater[s], or complex one[s] with scalloped edges, are some of the most prominent topographic features on Io. Paterae on Io are unique, yet in some aspects they resemble calderas known and studied on Earth, Mars, and Venus. They have steep walls, flat floors, and arcuate margins and sometimes exhibit nesting, all typical of terrestrial and Martian basalt shield calderas. However, they are much larger, many are irregular in shape, and they typically lack shields. Their great sizes (some > 200 km diameter) and lack of associated volcanic edifices beg comparison with terrestrial ash flow calderas; however, there is no convincing evidence on Io for the high-silica erupted products or dome resurgence associated with this type of caldera. Ionian paterae seem to be linked with the eruption of large amounts of mafic to ultramafic lavas and colorful sulfur-rich materials that cover the floors and sometimes flow great distances away from patera margins. They are often angular in shape or are found adjacent to mountains or plateaus, indicating tectonic influences on their formation. A database of 417 paterae on Io measured from images with <3.2 km pixel-1 resolution (80% of its surface) reveals that their mean diameter of 41.0 km is close to that for calderas of Mars (47.7 km), is smaller than that for Venus (~68 km), but dwarfs those for terrestrial basalt shield calderas (6.6 km) and ash flow calderas (18.7 km). Thirteen percent of all paterae are found adjacent to mountains, 42% have straight or irregular margins, and 8% are found atop low shields. Abundant, smaller paterae with more continuously active lava eruptions are found between 25°S and 25°N latitude, whereas fewer and larger paterae are found poleward of these latitudes. Patera distribution shows peaks at 330°W and 150°W longitude, likely related to the direction of greatest tidal massaging by Jupiter."
"Wonderful colors in a volcanic crater named Tupan Patera on Jupiter's moon Io, as seen in [in the second image down on the right] from NASA's Galileo spacecraft, show varied results of lava interacting with sulfur-rich materials."
"The colorfulness of the image is only slightly enhanced from what the human eye would see on the scene. The red in the image includes a small amount of infrared energy. Tupan Patera, named after a Brazilian thunder god, was seen as an active hot spot in earlier Galileo observations, but those low-resolution views did not show details of volcanic activity. This image taken in October 2001 at a resolution of 135 meters (443 feet) per picture element reveals the complex nature of the crater."
"Tupan is now clearly shown to be a volcanic depression, about 75 kilometers (47 miles) across, surrounded by cliffs about 900 meters (3000 feet) tall. In the center is a large area that must be higher than the rest of the crater floor because it has not been covered by the dark lavas. Much of the area is coated with a diffuse red deposit that Galileo scientists believe has condensed from sulfur gas escaping from volcanic vents. The floor of Tupan is covered with a surreal pattern of dark black, green, red, and yellow materials. The black material is recent, still-warm lava. The yellow is presumed to be a mix of sulfurous compounds, and the green appears to form where red sulfur has interacted with the dark lavas. While Galileo scientists have found previous evidence for both molten sulfur and molten rock on Io, this image shows the best evidence to date of chemical reactions taking place between the two."
"The intermingled patches of sulfur and lava are difficult to explain. The yellowish sulfur may be melting from within the crater walls over solidified but warm lava. The sulfur may boil away from the areas too hot for liquid sulfur to sit on, leaving patches where the dark lava is still visible."
"North is to the top of the image and the Sun illuminates the surface from the upper right."
Volcanicity[edit | edit source]
"The rates of volcanic resurfacing on Io are estimated on the basis of two separate observations [...] the lack of observable impact craters and assuming a Jovian cratering rate similar to those of the moon and Mars are found to be on the order of 0.1 cm/year. Estimated deposition rates of volcanic matter are [...] in general agreement with cratering rate determinations, if large particle deposition, undetected volcanic activity, volcanic flows and gas condensation are taken into account. Escape rates from Io estimated for sulfur, oxygen and sodium, based on their concentrations around Io, indicate that only a fraction of the present volcanic material can escape."
"This color image [on the right], acquired during Galileo's ninth orbit (C9) around Jupiter, shows two volcanic plumes on Io. One plume was captured on the bright limb or edge of the moon, erupting over a caldera (volcanic depression) named Pillan Patera. The plume seen by Galileo is 140 kilometers (86 miles) high, and was also detected by the Hubble Space Telescope. The Galileo spacecraft will pass almost directly over Pillan Patera in 1999 at a range of only 600 (373 miles). The second plume, seen near the terminator, the boundary between day and night, is called Prometheus after the Greek fire god). The shadow of the airborne plume can be seen extending to the right of the eruption vent. (The vent is near the center of the bright and dark rings). Plumes on Io have a blue color, so the plume shadow is reddish. The Prometheus plume can be seen in every Galileo image with the appropriate geometry, as well as every such Voyager image acquired in 1979. It is possible that this plume has been continuously active for more than 18 years. In contrast, a plume has never been seen at Pillan Patera prior to the recent Galileo and HST images."
"Color images from orbit C9 have been merged with a high resolution mosaic of images acquired in various orbits to enhance the surface detail. PIA00703 is another version of this image which also includes detailed insets of the plumes."
"North is to the top of the picture. The resolution is about 2 kilometers (1.2 miles) per picture element. This composite uses images taken with the green, violet, and near-infrared filters of the Solid State Imaging (CCD) system on NASA's Galileo spacecraft. The C9 images were obtained on June 28, 1997 at a range of more than 600,000 kilometers (372,000 miles)."
"The Solid-State Imaging (SSI) instrument provided the first high- and medium-resolution views of Io as the Galileo spacecraft closed in on the volcanic body in late 1999 and early 2000. While each volcanic center has many unique features, the majority can be placed into one of two broad categories. The "Promethean" eruptions, typified by the volcanic center Prometheus, are characterized by long-lived steady eruptions producing a compound flow field emplaced in an insulating manner over a period of years to decades. In contrast, "Pillanian" eruptions are characterized by large pyroclastic deposits and short-lived but high effusion rate eruptions from fissures feeding open-channel or open-sheet flows. Both types of eruptions commonly have ∼100-km-tall, bright, SO2-rich plumes forming near the flow fronts and smaller deposits of red material that mark the vent for the silicate lavas."
"Culann Patera, one of the most colorful volcanic centers on Io, is the centerpiece of this mosaic of the best high-resolution, color view of Io yet returned by NASA's Galileo spacecraft. The picture was constructed from images taken through the red, green, and violet filters of Galileo camera and has been processed to enhance the color variations. The resolution is about 200 meters (or yards) per picture element, and north is to the top."
"The color mosaic [second image down on the right] shows the complex relationships between the diffuse red deposit, the more confined green deposit, and the various colored lava flows. Culanns central caldera (above and to the right of center) has a highly irregular, scalloped margin and a green-colored floor. Lava flows spill out of the caldera on all sides. A dark red, curving line extending northwest from the southwestern tip of the caldera may mark a crusted-over lava tube feeding the dark (and hot) silicate flows to the northwest. Unusual dark red flows to the southeast of the caldera may be sulfur flows or silicate flows whose surfaces have been modified. The diffuse red material around the caldera is believed to be a compound of sulfur deposited from a plume of gas."
"Culanns caldera and several lava flows extending from the caldera are coated by greenish materials. Green material can also be seen in the caldera to the lower right of the image, named Tohil Patera. The greenish material often has sharp boundaries, so it is apparently confined to the caldera floor and the dark flows. Galileo scientists are investigating whether the greenish material forms as a coating of sulfur-rich material on warm silicate lavas."
"The images were taken on November 25, 1999 during Galileo's 25th orbit at a distance of 20,000 kilometers (12,500 miles) from Io."
"NASA's Galileo spacecraft caught this volcanic eruption in action on Jupiter's moon Io on November 25, 1999. This mosaic shows Tvashtar Catena, a chain of calderas, in enhanced color. It combines low resolution (1.3 kilometers, or .8 miles, per picture element) color images of Io taken on July 3, 1999 with the much higher resolution (180 meters, or 197 yards, per picture element) black and white images taken in November. The molten lava was hot enough, and therefore bright enough, to saturate, or overexpose, Galileo's camera (original image is inset in lower right corner). The bright lava curtain (a chain of lava fountains) and surface flows shown in the color image were assembled as an interpretive drawing by Galileo scientists, based on their knowledge of how the camera behaves when saturated. The lava appears to be producing fountains to heights of up to 1.5 kilometers (5,000 feet) above the surface. Several other lava flows can be seen on the floors of the calderas. The darkest flows are probably the most recent."
"The elongated caldera in the center of the image is almost surrounded by a mesa that is about 1 kilometer (.6 miles) high. In places the mesas margins are scalloped, which is typical of an erosional process called sapping. This occurs when fluid escapes from the base of a cliff, causing the material above it to collapse. On Earth, sapping is caused by springs of groundwater. Similar features on Mars are one of the key pieces of evidence that water flowed on Mars surface in the past. On Io, the fluid is believed to be sulfur dioxide, which should vaporize almost instantaneously when it reaches the near vacuum at Io's surface, blasting away material at the base of the cliffs."
"North is to the top of the image and the Sun illuminates the surface from the lower left. The high resolution black and white image was taken at a distance of 17,000 kilometers (11,000 miles)."
"These images [fourth down on the right] of Jupiter's volcanic moon, Io, show the results of a dramatic event that occurred on the fiery satellite during a five-month period. The changes, captured by the solid state imaging (CCD) system on NASA's Galileo spacecraft, occurred between the time Galileo acquired the left frame, during its seventh orbit of Jupiter, and the right frame, during its tenth orbit. A new dark spot, 400 kilometers (249 miles) in diameter, which is roughly the size of Arizona, surrounds a volcanic center named Pillan Patera. Galileo imaged a 120 kilometer (75 mile) high plume erupting from this location during its ninth orbit. Pele, which produced the larger plume deposit southwest of Pillan, also appears different than it did during the seventh orbit, perhaps due to interaction between the two large plumes. Pillan's plume deposits appear dark at all wavelengths. This color differs from the very red color associated with Pele, but is similar to the deposits of Babbar Patera, the dark feature southwest of Pele. Some apparent differences between the images are not caused by changes on Io's surface, but rather are due to differences in illumination, emission and phase angles. This is particularly apparent at Babbar Patera."
"North is to the top of the images. The left frame was acquired on April 4th, 1997, while the right frame was taken on Sept. 19th, 1997. The images were obtained at ranges of 563,000 kilometers (350,000 miles) for the left image, and 505,600 kilometers (314,165 miles) for the right."
Hypotheses[edit | edit source]
- Io is more volcanic than any rocky-object of its size because of the electrical currents running through it.
See also[edit | edit source]
References[edit | edit source]
- Ian O'Neill (4 August 2014). "Jupiter Moon Io Unleashes Cataclysmic Eruptions". Discovery.com. Retrieved 2015-05-10.
- Imke de Pater (4 August 2014). "Jupiter Moon Io Unleashes Cataclysmic Eruptions". Discovery.com. Retrieved 2015-05-10.
- Ashley Davies (4 August 2014). "Jupiter Moon Io Unleashes Cataclysmic Eruptions". Discovery.com. Retrieved 2015-05-10.
- Mike Wall (6 April 2013). "Volcanoes on Jupiter's Moon Io Are All Wrong". Space.com. Retrieved 2015-05-11.
- Christopher Hamilton (6 April 2013). "Volcanoes on Jupiter's Moon Io Are All Wrong". Space.com. Retrieved 2015-05-11.
- Rosaly MC Lopes (2006). "Io: The Volcanic Moon". In Lucy-Ann McFadden. Encyclopedia of the Solar System. Academic Press. pp. 419–431. ISBN 978-0-12-088589-3.
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- Sue Lavoie (October 2001). "PIA02599: Colorful Tupan Patera, Io". Pasadena, California USA: NASA/JPL. Retrieved 2017-07-21.
- T. V. Johnson, A. F. Cook II, C. Sagan & L. A. Soderblom (30 August 1979). "Volcanic resurfacing rates and implications for volatiles on Io". Nature 280 (5725): 746-750. doi:10.1038/280746a0. http://www.nature.com/nature/journal/v280/n5725/abs/280746a0.html?foxtrotcallback=true. Retrieved 2017-07-21.
- Sue Lavoie (17 November 1997). "PIA01081: Color Mosaic and Active Volcanic Plumes on Io". Pasadena, California USA: NASA/JPL. Retrieved 2017-07-21.
- L. Keszthelyi, A. S. McEwen, C. B. Phillips, M. Milazzo, P. Geissler, E. P. Turtle, J. Radebaugh, D. A. Williams, D. P. Simonelli, H. H. Breneman, K. P. Klaasen, G. Levanas, T. Denk (25 December 2001). "Imaging of volcanic activity on Jupiter's moon Io by Galileo during the Galileo Europa Mission and the Galileo Millennium Mission". Journal of Geophysical Research Planets 106 (E12): 33025–33052. doi:10.1029/2000JE001383. http://onlinelibrary.wiley.com/doi/10.1029/2000JE001383/abstract;jsessionid=EDC031AA7C710E2F99E40E2564278A17.f02t03. Retrieved 2017-07-21.
- Sue Lavoie (25 November 1999). "PIA02535: Culann Patera, Io, in False Color". Pasadena, California USA: NASA/JPL. Retrieved 2017-07-21.
- Sue Lavoie (3 July 1999). "PIA02545: Eruption at Tvashtar Catena, Io, in Color". Pasadena, California USA: NASA/JPL. Retrieved 2017-07-21.
- Sue Lavoie (19 September 1997). "PIA00744: Arizona-sized Io Eruption". Pasadena, California USA: NASA/JPL. Retrieved 2017-07-21.