From Gemini Observatory: “Discovering Patterns in Io’s Volcanoes”


Gemini Observatory
From Gemini Observatory

August 5, 2019

Orbital Resonnances of the Galilean Moons of Jupiter. Animation of the 1:2:4 Laplace resonance between Ganymede, Europa, and Io. The labels indicate the ratios of orbital periods: Europa’s is twice Io’s, and Ganymede’s is four times Io’s. Credit: Matma Rex/Wikicommons.

Jupiter’s volcanic moon Io brought astronomers and geologists together to reveal that this moon’s hot spots fluctuate on unexpected timescales.

NASA’s Galileo spacecraft acquired its highest resolution images of Jupiter’s moon Io on 3 July 1999 during its closest pass to Io since orbit insertion in late 1995. This color mosaic uses the near-infrared, green and violet filters (slightly more than the visible range) of the spacecraft’s camera and approximates what the human eye would see. Most of Io’s surface has pastel colors, punctuated by black, brown, green, orange, and red units near the active volcanic centers. A false color version of the mosaic has been created to enhance the contrast of the color variations.

The improved resolution reveals small-scale color units which had not been recognized previously and which suggest that the lavas and sulfurous deposits are composed of complex mixtures (Cutout A of false color image). Some of the bright (whitish), high-latitude (near the top and bottom) deposits have an ethereal quality like a transparent covering of frost (Cutout B of false color image). Bright red areas were seen previously only as diffuse deposits. However, they are now seen to exist as both diffuse deposits and sharp linear features like fissures (Cutout C of false color image). Some volcanic centers have bright and colorful flows, perhaps due to flows of sulfur rather than silicate lava (Cutout D of false color image). In this region bright, white material can also be seen to emanate from linear rifts and cliffs.

Comparison of this image to previous Galileo images reveals many changes due to the ongoing volcanic activity.

Galileo will make two close passes of Io beginning in October of this year. Most of the high-resolution targets for these flybys are seen on the hemisphere shown here.

North is to the top of the picture and the sun illuminates the surface from almost directly behind the spacecraft. This illumination geometry is good for imaging color variations, but poor for imaging topographic shading. However, some topographic shading can be seen here due to the combination of relatively high resolution (1.3 kilometers or 0.8 miles per picture element) and the rugged topography over parts of Io. The image is centered at 0.3 degrees north latitude and 137.5 degrees west longitude. The resolution is 1.3 kilometers (0.8 miles) per picture element. The images were taken on 3 July 1999 at a range of about 130,000 kilometers (81,000 miles) by the Solid State Imaging (SSI) system on NASA’s Galileo spacecraft during its twenty-first orbit.

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA’s Office of Space Science, Washington, DC.
This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL Background information and educational context for the images can be found at URL

The team utilized the Gemini North telescope [below] and the W.M. Keck Observatory, both located on Maunakea, Hawaiʻi Island.

Keck Observatory, operated by Caltech and the University of California, Maunakea Hawaii USA, 4,207 m (13,802 ft)

The Gemini observations, which provided about 80% of the data for the study, employed the high-resolution adaptive optics system ALTAIR combined with the Gemini Near InfraRed Imager and spectrograph (NIRI). The researchers conducted a total of 271 observations between 2013 and 2018 and published their results in the July 2019 issue of The Astronomical Journal and the June 28, 2019 issue Geophysical Research Letters.

While whizzing around Jupiter in an elliptical orbit with a period of only 1.8 days, Io’s interior is warmed by the varying pull of Jupiter’s gravity, roughly similar to how the Earth’s moon causes tides on our planet. This “tidal heating” powers Io’s volcanoes. However, the shape of Io’s orbit also changes, becoming alternately rounder and then more elliptical, over a longer period of about 480 days. The variation in Io’s orbital shape is caused by the more subtle effects of the varying gravitational pulls from Jupiter’s other large moons, mainly Europa and Ganymede.

By studying changes in Io’s surface brightness due to its volcanic activity, researchers discovered a pattern in the volcanism that appears to coincide with the 480-day variation in the moon’s orbital shape. This was unexpected because there is no detectable pattern associated with the 1.8-day period of a single orbit, even though this is the amount of time over which the most dramatic variations in the pull of gravity occur. To understand this puzzling result, the researchers note that the magma is likely too viscous to react to the changing gravity on the timescale of one orbit, but it can adjust its flow rate with the slower variation in the shape of Io’s orbit. This explains the long-term variations in the degree of volcanic activity.

Read more about this discovery and Io’s most powerful, persistent volcano, Loki Patera in this story from the American Geophysical Union.

See the full article here .

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NOAO Gemini North on MaunaKea, Hawaii, USA, Altitude 4,213 m (13,822 ft)

Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

Gemini’s mission is to advance our knowledge of the Universe by providing the international Gemini Community with forefront access to the entire sky.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai’i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country’s contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, and the Brazilian Ministério da Ciência, Tecnologia e Inovação. The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.