NASA\u2019s Juno spacecraft was sent to Jupiter to study the gas giant. But its mission was extended, giving it an opportunity to study the unique moon Io. Io is the most volcanically active body in the Solar System, with over 400 active volcanoes.<\/p>\n
Researchers have taken advantage of Juno\u2019s flybys of Io to study how tidal heating affects the moon. <\/p>\n
<\/p>\n In recent months, Juno performed several flybys of Io, culminating in one that brought the spacecraft to within 1500 km of the surface. This gave Juno unprecedented close-up views of the volcanic moon. One of its instruments, the Jovian Infrared Auroral Mapper (JIRAM), is an infrared spectrometer, and its data is at the heart of new research into Io\u2019s volcanic activity and how tidal heating drives it. <\/p>\n The new research letter, \u201cJIRAM Observations of Volcanic Flux on Io: Distribution and Comparison to Tidal Heat Flow Models,\u201d<\/span> was published in the journal Geophysical Research Letters. Madeline Pettine, a doctoral student in astronomy at Cornell University, is the lead author.<\/p>\n Though Io is dead, the tidal heating that keeps it warm could contribute to habitability elsewhere. <\/p>\n \u201cStudying the inhospitable landscape of Io\u2019s volcanoes actually inspires science to look for life,\u201d said lead author Pettine.<\/p>\n \u201cIt\u2019s easier to study tidal heating on a volcanic world rather than peering through a kilometers-thick ice shell that\u2019s keeping the heat covered up.\u201d<\/p>\n Madeline Pettine, Cornell University<\/cite><\/p><\/blockquote>\n<\/figure>\n Io is one of the four Galilean moons. The other three, Callisto, Ganymede, and Europa, are all suspected of having liquid oceans under frozen layers of surface ice. If these oceans truly exist, they could potentially support life. Jupiter\u2019s tidal heating provides the heat to keep those oceans warm. Io is valuable scientifically because we can witness the effects of tidal heating on its surface. <\/p>\n \u201cTidal heating plays an important role in the heating and orbital evolution of celestial bodies,\u201d said co-author Alex Hayes, the Jennifer and Albert Sohn Professor of Astronomy in the College of Arts and Sciences at Cornell. \u201cIt provides the warmth necessary to form and sustain subsurface oceans in the moons around giant planets like Jupiter and Saturn.\u201d<\/p>\n Io\u2019s volcanoes aren\u2019t distributed evenly on its surface. The majority of them are in the equatorial region. However, in this work, the researchers found that the volcanoes on Io\u2019s poles may act to regulate the moon\u2019s interior temperature. <\/p>\n \u201cI\u2019m trying to match the pattern of volcanoes on Io and the heat flow that they\u2019re producing with the heat flow we expected from theoretical models,\u201d said Pettine.<\/p>\n Jupiter is the most massive planet in the Solar System and its gravitational pull is second only to the Sun\u2019s. Jupiter\u2019s powerful gravity does more than dictate Io\u2019s orbit. It warps the moon and forces it to deform, generating heat. <\/p>\n \u201cThe gravity from Jupiter is incredibly strong,\u201d Pettine said. \u201cConsidering the gravitational interactions with the large planet\u2019s other moons, Io ends up getting bullied, constantly stretched and scrunched up. With that tidal deformation, it creates a lot of internal heat within the moon.\u201d<\/p>\n Io has no ocean, so the heat melts rock, creating a likely magma ocean inside the moon. That magma works its way up through the surface, erupting as volcanoes and lava flows. The gases from the magma colour the surface of the moon in reds, yellows, and browns. \u00a0<\/p>\n To understand what\u2019s happening inside Io, Pettine and her colleagues worked with a mathematical equation called spherical harmonic decomposition. This equation allows scientists to analyze data from a spherical surface and break it down, revealing patterns and important features. <\/p>\n Previous research shows that most of Io\u2019s volcanic activity is in its equatorial region, although some volcanoes have been detected on its poles. In this work, it revealed systems of bright volcanoes at high latitudes. <\/p>\n \u201cOur observations confirm previously detected systems of bright volcanoes at high latitudes,\u201d the authors write. \u201cWhile our map agrees with previous studies that suggest that low?to mid?latitude areas see the highest areas of volcanic activity, our map suggests that the poles of Io are comparably active to the equator.\u201d<\/p>\n Pettine and her co-researchers compared their global heat flux maps with three different models that attempt to explain what\u2019s going under Io\u2019s surface: the Deep Mantle model, the Asthenospheric model, and the Global Magma model. <\/p>\n The Deep Mantle Model says that tidal heating keeps a large portion of the mantle in a molten state. The Asthenospheric Model says that less of the mantle is molten and that only the asthenosphere is in a molten state due to tidal heating. This is more similar to Earth. The Global Magma Ocean model is a more extreme interpretation of the data and says that a greater portion of Io\u2019s interior is molten, perhaps extending from just below the surface to greater depths. <\/p>\n The researchers also created a complete global map of heat flux produced by volcanic hot spots. \u201cViewing this flux on both a linear and a logarithmic scale better illustrates individual volcanic behaviour and global heat flow variations, particularly the lowest-flux regions,\u201d the authors write. <\/p>\n \u201cOur study finds that both poles are comparably active and that the observed flux distribution is inconsistent with an asthenospheric heating model, although the south pole is viewed too infrequently to establish reliable trends,\u201d the authors explain. <\/p>\n The researchers say that their heat flux maps don\u2019t favour any of the models. \u201cUsing spherical decomposition, we find that the distribution of flux is much more uniform than in-line with any of the models,\u201d they write. <\/p>\n For now, a more complete understanding of Io\u2019s tidal heating and volcanic activity is elusive. Juno\u2019s JIRAM observations are just a snapshot of the moon. Over longer time periods, the heat maps will look different and may support different models and conclusions.<\/p>\n \u201cI\u2019m not solving tidal heating with this one paper,\u201d said Pettine. \u201cHowever, if you think about icy moons in the outer solar system, other moons like Jupiter\u2019s Europa, or Saturn\u2019s Titan and Enceladus, they\u2019re the places that if we\u2019re going to find life in the solar system, it will be one of those places.\u201d<\/p>\n A better understanding of tidal heating will do more than explain aspects of our own Solar System. It may help us understand habitable zones in other solar systems and how exomoons might be heated by giant exoplanets. <\/p>\n That\u2019s why, although Jupiter\u2019s icy moons are prime targets for exploration, with two missions heading to study Europa, Ganymede, and Callisto, we need to keep a scientific eye on Io.<\/p>\n \u201cWe need to know how the heat is being generated,\u201d Pettine said. \u201cIt\u2019s easier to study tidal heating on a volcanic world rather than peering through a kilometers-thick ice shell that\u2019s keeping the heat covered up.\u201d<\/p>\n\n
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