Masubi (volcano)
Encyclopedia
Masubi is an active volcano
on Jupiter's
moon
Io
. It is located on Io's leading hemisphere at 49.6°S 56.18°W within a bright terrain region named Tarsus Regio. A volcanic plume has been observed at Masubi by various spacecraft starting with Voyager 1
in 1979, though it has not been persistent like similar Ionian volcanoes Amirani
and Prometheus
. Masubi is also notable for having one of the largest active lava flows on Io, with an additional 240-kilometer flow forming between 1999 and 2007.
was first observed during the Voyager 1 encounter with the Jupiter system on March 5, 1979. Voyager discovered a 64-kilometer tall, 177-kilometer wide volcanic dust plume, composed primarily of sulfur dioxide
, at the northern end of a 501-kilometer long dark lava flow. To date, images taken by Voyager 1's Imaging Science Sub-system Wide-Angle Camera shortly before the spacecraft's closest approach to Io have the highest spatial resolution coverage of this volcano at two kilometers per pixel
. These images reveal a lava flow with a V-shaped northern end, associated with the plume source as noted by the dark plume deposit ring surrounding it, and bifurcated southern section. The two-lobed shape of the plume deposit may result from the Masubi volcanic plume during Voyager 1 encounter having two sources on the flow field and two eruption columns. This was the faintest of the plumes on Io observed by the two Voyager spacecraft. It was initially designated as Plume 8, but in 1979 the International Astronomical Union
formally named
it Masubi, after a Japanese
fire god called Ho-Masubi
. The lava flow associated with the plume was named Masubi Fluctus shortly after the start of the Galileo mission.
to ultramafic composition.
February 28, 2007 encounter with the Jupiter system. During this encounter, two plumes were observed along Masubi Fluctus. One was seen at the northern end of the flow, interpreted as the main source vent for the flow. The second was observed near the middle of the elongated flow field. These two plumes were 70 and 80 kilometers tall respectively. New Horizons also observed a fresh, 240-kilometer lava flow at Masubi, which formed between Galileo's last observation of Masubi Fluctus in 1999 and the New Horizons flyby in 2007. This was the largest new lava flow observed anywhere in the solar system since extra-terrestrial volcanism was discovered on Io in 1979. The two plumes observed emanate from the northern and southern ends of this new flow. Fallout from the two volcanic plumes produced a two-lobed dark deposit around the new lava flow, similar to the deposit seen during the Voyager encounters.
New Horizons images also highlighted the fact that the visibility of the older, 500-km long flow varies depending on the phase angle
of the observation. Phase angle is the angle between the observer, Io, and the Sun. Io appears "full" at low phase angles near 0°, "half-full" at moderate phase angles near 90°, and crescent shaped at high phase angles approaching 180°. The older portion of Masubi Fluctus is nearly invisible at low phase angles and only shows up at high phase angles. This may be due to sulfur dioxide frost on top of the now cooled lava flow obscuring it, but this deposit is not yet thick enough to obscure the texture of the flow. A similar phase angle effect at Masubi Fluctus was also observed by Voyager and Galileo, though this was limited to longer visible wavelengths.
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 Jupiter's
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,...
moon
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
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 leading hemisphere at 49.6°S 56.18°W within a bright terrain region named Tarsus Regio. A volcanic plume has been observed at Masubi 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 like similar Ionian volcanoes Amirani
Amirani (volcano)
Amirani is an active volcano on Jupiter's moon Io. It is located on Io's leading hemisphere at .The volcano is responsible for the largest active lava flow in the entire Solar System, with recent flows dwarfing those of even other volcanos on Io...
and Prometheus
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...
. Masubi is also notable for having one of the largest active lava flows on Io, with an additional 240-kilometer flow forming between 1999 and 2007.
Observations by Voyager 1
The volcanoVolcanism on Io
Volcanism on Io, a moon of Jupiter, produces lava flows, volcanic pits, and plumes of sulfur and sulfur dioxide hundreds of kilometres high. This volcanic activity was discovered in 1979 by Voyager 1 imaging scientists...
was first observed during the Voyager 1 encounter with the Jupiter system on March 5, 1979. Voyager discovered a 64-kilometer tall, 177-kilometer wide volcanic dust plume, composed primarily of 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...
, at the northern end of a 501-kilometer long dark lava flow. To date, images taken by Voyager 1's Imaging Science Sub-system Wide-Angle Camera shortly before the spacecraft's closest approach to Io have the highest spatial resolution coverage of this volcano at two kilometers per pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
. These images reveal a lava flow with a V-shaped northern end, associated with the plume source as noted by the dark plume deposit ring surrounding it, and bifurcated southern section. The two-lobed shape of the plume deposit may result from the Masubi volcanic plume during Voyager 1 encounter having two sources on the flow field and two eruption columns. This was the faintest of the plumes on Io observed by the two Voyager spacecraft. It was initially designated as Plume 8, but in 1979 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...
formally 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...
it Masubi, after a Japanese
Japanese mythology
Japanese mythology is a system of beliefs that embraces Shinto and Buddhist traditions as well as agriculturally based folk religion. The Shinto pantheon comprises innumerable kami...
fire god called Ho-Masubi
Kagu-tsuchi
, also called , , or , is the kami of fire in Japanese mythology.-Mythology:Kagu-tsuchi's birth burned his mother Izanami, causing her death. His father Izanagi, in his grief, beheaded Kagu-tsuchi with his sword, Ame no Ohabari , and cut his body into eight pieces, which became eight volcanoes...
. The lava flow associated with the plume was named Masubi Fluctus shortly after the start of the Galileo mission.
Observations by Galileo
The Galileo spacecraft and ground-based astronomers observed volcanic activity at Masubi on several occasions in the late 1990s, but it was not a persistent thermal hotspot. The camera on Galileo observed a volcanic plume along Masubi Fluctus during the Galileo extended missions, in July/August 1999 and August 2001. Galileo's cameras also observed a plume deposit form in September 1997. In each of these cases, the volcanic plumes emanated from different parts of Masubi Fluctus, providing further evidence that dust plumes like the one at Masubi result from the rapid sublimation of surficial sulfur dioxide frost by warm, advancing lava flow fronts, rather than erupting from the primary volcanic vent. Ground-based astronomers in August 1998 briefly observed a high-temperature eruption at Masubi, confirming Masubi Fluctus' silicate maficMafic
Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...
to ultramafic composition.
Observations by New Horizons
Masubi was last observed by a spacecraft during New HorizonsNew 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...
February 28, 2007 encounter with the Jupiter system. During this encounter, two plumes were observed along Masubi Fluctus. One was seen at the northern end of the flow, interpreted as the main source vent for the flow. The second was observed near the middle of the elongated flow field. These two plumes were 70 and 80 kilometers tall respectively. New Horizons also observed a fresh, 240-kilometer lava flow at Masubi, which formed between Galileo's last observation of Masubi Fluctus in 1999 and the New Horizons flyby in 2007. This was the largest new lava flow observed anywhere in the solar system since extra-terrestrial volcanism was discovered on Io in 1979. The two plumes observed emanate from the northern and southern ends of this new flow. Fallout from the two volcanic plumes produced a two-lobed dark deposit around the new lava flow, similar to the deposit seen during the Voyager encounters.
New Horizons images also highlighted the fact that the visibility of the older, 500-km long flow varies depending on the phase angle
Phase angle (astronomy)
Phase angle in astronomical observations is the angle between the light incident onto an observed object and the light reflected from the object...
of the observation. Phase angle is the angle between the observer, Io, and the Sun. Io appears "full" at low phase angles near 0°, "half-full" at moderate phase angles near 90°, and crescent shaped at high phase angles approaching 180°. The older portion of Masubi Fluctus is nearly invisible at low phase angles and only shows up at high phase angles. This may be due to sulfur dioxide frost on top of the now cooled lava flow obscuring it, but this deposit is not yet thick enough to obscure the texture of the flow. A similar phase angle effect at Masubi Fluctus was also observed by Voyager and Galileo, though this was limited to longer visible wavelengths.