Pele is an active volcano

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 on the surface of Jupiter

Jupiter

Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

's moon Io

Io (moon)

Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....

. It is located on Io's trailing hemisphere at 18.7°S 255.3°W A large, 300 kilometres (186.4 mi) tall volcanic plume has been observed at Pele by various spacecraft starting with Voyager 1

Voyager 1

The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...

in 1979, though it has not been persistent. The discovery of the Pele plume on March 8, 1979 confirmed the existence of active volcanism on Io. The plume is associated with a lava lake

Lava lake

Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression. The term is used to describe both lava lakes that are wholly or partly molten and those that are solidified...

 at the northern end of the mountain Danube Planum

Danube Planum

Danube Planum is a rifted mesa on the surface of Jupiter's moon Io. It is located on Io's trailing hemisphere at . Danube Planum is 244.22 kilometers across and 5.5 km tall...

. Pele is also notable for a persistent, large red ring circling the volcano resulting from sulfurous fallout from the volcanic plume.

Voyager

As Voyager 1

Voyager 1

The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...

approached the Jupiter system in March 1979, it acquired numerous images of the planet and its four largest satellites, including Io. One of the most distinctive features of these distant images of Io was a large, elliptical, footprint-shaped ring on the satellite's trailing hemisphere (the side facing away from the direction of motion in a synchronously-rotating satellite like Io). During the encounter itself on March 5, 1979, Voyager 1 acquired high-resolution images of the footprint-shaped region. At the center of bow tie

Bow tie

The bow tie is a type of men's necktie. It consists of a ribbon of fabric tied around the collar in a symmetrical manner such that the two opposite ends form loops. Ready-tied bow ties are available, in which the distinctive bow is sewn into shape and the band around the neck incorporates a clip....

-shaped dark region in the middle of the ring was a depression partially filled with dark material, 30 km (18.6 mi) by 20 km (12.4 mi) in size. This depression, later found to be the source of the Pele volcano, is at the northern base of a rifted mountain later named Danube Planum. With the other dramatic evidence for volcanic activity on the surface of Io from this encounter, researchers hypothesized that Pele was likely a caldera

Caldera

A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

.

On March 8, 1979, three days after passing Jupiter, Voyager 1 took images of Jupiter's moons to help mission controllers determine the spacecraft's exact location, a process called optical navigation. While processing images of Io to enhance the visibility of background stars, navigation engineer Linda Morabito

Linda A. Morabito

Linda A. Morabito , also known as Linda Kelly, Linda Hyder, and Linda Morabito-Meyer, is the astronomer who made the discovery of volcanic activity on Io, a moon of Jupiter, on March 9, 1979, at NASA's Jet Propulsion Laboratory...

 found a 300 kilometres (186.4 mi) tall cloud along the moon's limb. At first, she suspected the cloud to be a moon behind Io, but no suitably sized body would have been in that location. The feature was determined to be a volcanic plume 300 km (186.4 mi) tall and 1200 km (745.6 mi) wide, generated by active volcanism at Pele. Based on the size of the plume observed at Pele, the ring of reddish (or dark as it appeared to Voyager's cameras, which were insensitive to red-wavelengths) material was determined to be a deposit of plume material. Following this discovery, seven other plumes were located in earlier Voyager images of Io. Thermal emission from Pele detected by the Voyager 1 Infrared Interferometer Spectrometer (IRIS) detected a thermal hotspot at Pele, indicative of cooling lava, further indicating that volcanic activity at the surface was linked to the plumes observed by Voyager 1.

When Voyager 2

Voyager 2

The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...

flew through the Jupiter system in July 1979, its imaging campaign was modified to observe Io's plumes in action and to look for surface changes. Pele's plume, designated Plume 1 at the time as it was the first of Io's volcanic plumes to be discovered, was not seen by Voyager 2 four months later. Surface monitoring observations revealed changes with the red ring surrounding Pele. While it was heart- or hoofprint-shaped during the Voyager 1 encounter, it was now more elliptical with the notch in the southern part of the plume deposit now filled in, possibly due to changes in the distribution of plume sources within the Pele patera.

Following the Voyager encounters, the International Astronomical Union

International Astronomical Union

The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...

 officially named

Planetary nomenclature

Planetary nomenclature, like terrestrial nomenclature, is a system of uniquely identifying features on the surface of a planet or natural satellite so that the features can be easily located, described, and discussed. The task of assigning official names to features is taken up by the International...

 the volcano after the Hawaiian

Hawaiian mythology

Hawaiian mythology refers to the legends, historical tales and sayings of the ancient Hawaiian people. It is considered a variant of a more general Polynesian mythology, developing its own unique character for several centuries before about 1800. It is associated with the Hawaiian religion...

 volcano goddess, Pele, in 1979.

Galileo and beyond

Galileo arrived at the Jupiter system in 1995 and, from 1996 to 2001, regularly monitored volcanic activity on Io through observations of Io's thermal emission at near-infrared wavelengths, imaging Io while it was in the Jupiter's shadow in order to look for thermal hotspots at visible and near-infrared wavelengths, and imaging Io during most orbit in order to detect changes in the appearance of diffuse material and lava flows on the surface. Thermal emission from Pele was detected in nearly every occasion Io's trailing hemisphere was imaged while the moon was in the shadow of Jupiter. The volcanic plume at Pele was found to be intermittent or primarily composed of gas with occasional bursts of increased dust content. It was detected only twice by Galileo in December 1996 and December 2000. In these two detections, the plume height varied from 300 km (186.4 mi) to 426 km (264.7 mi). The plume was also detected by the Hubble Space Telescope

Hubble Space Telescope

The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 in October 1999 while Galileo was conducting a flyby of the moon. The Hubble observations allowed for the detection of diatomic sulfur

Sulfur

Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 (S₂) for the first time on Io in Pele's plume. Subtle changes in the shape and intensity of the large red-ring plume deposit surrounding Pele were observed in daylight images of the volcano, with the most notable change seen in September 1997 when dark pyroclastic material

Pyroclastic flow

A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...

 from an eruption of Pillan Patera

Pillan Patera

Pillan Patera is a patera, or a complex crater with scalloped edges, on Jupiter's moon Io. It is located at , south of Pillan Mons and west of Reiden Patera. It is named after the Araucanian thunder, fire, and volcano god. Its name was approved by the International Astronomical Union in 1997.Pillan...

 covered up a portion of Pele's plume deposit.

During Galileo's encounters with Io between October 1999 and October 2001, the spacecraft observed Pele on three occasions using its camera and infrared spectrometers while the volcano was on Io's night-side. The cameras revealed a curved line of bright spots along the margin of the Pele patera (a term used for volcanic depressions on Io, akin to calderas). Within the east-west dark band along the southeastern portion of the patera, a large amount of thermal emission was observed, with temperatures and distribution consistent with a large, basaltic lava lake.

Thermal emission at Pele was also seen in December 2000 by the Cassini spacecraft, in December 2001 from the Keck Telescope in Hawaii

Hawaii

Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

, and by the New Horizons

New Horizons

New Horizons is a NASA robotic spacecraft mission currently en route to the dwarf planet Pluto. It is expected to be the first spacecraft to fly by and study Pluto and its moons, Charon, Nix, Hydra and S/2011 P 1. Its estimated arrival date at the Pluto-Charon system is July 14th, 2015...

spacecraft in February 2007.

Lava lake

The Pele volcano consists of a volcanic crater, also known a patera, 30 km (18.6 mi) by 20 km (12.4 mi) in size. Pele lies at the base of the northern tip of the mountain Danube Planum. The patera has multiple floor levels, with a higher north-eastern section and a lower section that consists of an east-west-trending graben

Graben

In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....

. Volcanic activity at Pele, as seen in images taken by Galileo in October 2001 while Pele was on Io's night side, appears to be limited to small thermal "hot-spots" along the margins of the patera and a more intense thermal emission source with in a dark area in the southeast portion of the patera floor. This distribution of activity, combined with Pele's stability as a hotspot in terms of temperature and power emitted, suggests that Pele is a large, active lava lake

Lava lake

Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression. The term is used to describe both lava lakes that are wholly or partly molten and those that are solidified...

, a combination of eruption style and intensity of activity not seen elsewhere on Io. The small hotspots seen in the Galileo data represent areas where the crust of the lava lake breaks up along the margins of the patera, allowing fresh lava to become exposed at the surface. The southeastern portion of the patera, an area of dark terrain in Voyager 1 imagery, is the most active region of the Pele volcano, with the most extensive region of hot lava at Pele. This area is thought to be a vigorously overturning lava lake, suggestive of a combination of a large mass flux of lava to the lake from a magma reservoir below the surface and a large mass fraction of dissolved volatiles like sulfur dioxide

Sulfur dioxide

Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

 and diatomic sulfur

Sulfur

Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

. Given Pele's brightness at near-infrared wavelengths, activity at this portion of the lava lake may also result in lava fountain

Lava fountain

A lava fountain is a volcanic phenomenon in which lava is forcefully but non-explosively ejected from a crater, vent, or fissure. Lava fountains may reach heights of up to . They may occur as a series of short pulses, or a continuous jet of lava. They are commonly seen in Hawaiian eruptions.-See...

ing.

Lava temperatures measured using the near-infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 emission spectrum

Emission spectrum

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted by the element's atoms or the compound's molecules when they are returned to a lower energy state....

 of thermal hotspots observed at Pele are consistent with silicate basaltic lava erupting at the lava lake. The measurements from Galileo and Cassini

Cassini-Huygens

Cassini–Huygens is a joint NASA/ESA/ASI spacecraft mission studying the planet Saturn and its many natural satellites since 2004. Launched in 1997 after nearly two decades of gestation, it includes a Saturn orbiter and an atmospheric probe/lander for the moon Titan, although it has also returned...

images of Pele suggest peak temperatures of at least 1250-1350°C, while the near-infrared spectrometer on Galileo found peak temperatures of 1250-1280°C. While Pele's energy output and temperature remained consistent on the timescale of months to years throughout much of the Galileo missions, measurements of Pele's brightness using Cassini data taken during an eclipse

Eclipse

An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...

 of Io by Jupiter found considerable variations on the timescale of minutes. This is consistent with variations in the distribution and size of lava fountains at Pele over that timeframe.

Plume

Pele's plume is the archetypal

Archetype

An archetype is a universally understood symbol or term or pattern of behavior, a prototype upon which others are copied, patterned, or emulated...

 Pele-type plume: 300 km (186.4 mi) tall, producing a large reddish deposit that is concentric around the source vent. The plume is created from the degassing of sulfur (S₂) and sulfur dioxide (SO₂) from erupting lava in the Pele lava lake. Images of the plume taken by Voyager 1 revealed a large structure without a central column like the smaller, Prometheus-type

Prometheus (volcano)

Prometheus is an active volcano on Jupiter's moon Io. It is located on Io's hemisphere facing away from Jupiter at . Prometheus consists of a -wide volcanic pit named Prometheus Patera and a -long compound lava flow, all surrounded by reddish sulfur and circular, bright sulfur dioxide volcanic...

plumes, but instead having a filamentary structure. This morphology is consistent with a plume that is formed by sulfurous gases erupted skyward from the Pele lava lake, which then condense into solid S₂ and SO₂ when they reach the shock canopy along the outer edge of the umbrella-shaped plume. These condensed materials then are deposited onto the surface, forming a large, red, oval-shaped ring around the Pele volcano. The oval shape of the deposits, elongated in roughly the north-south direction, may be the result of an east-west, linear source region, consistent with the shape and orientation of the graben that forms the southern and more active portion of the Pele patera. Variable activity in different portions of the Pele lava lake may also result in the changes in brightness and shape of the plume deposit over time observed by various spacecraft.