Tawhaki Vallis
Encyclopedia
Tawhaki Vallis is a shallow valley on Jupiter's
moon
Io
. It is located on Io's leading hemisphere in the equatorial plains of western Media Regio at 0.5°N 72.8°W. The valley is 190 kilometers long, 0.5 to 6 km wide, and 40 to 65 meters deep. Due to the shallow depth and lack of brightness or color variations associated with it, Tawhaki Vallis was seen in only a single, high spatial resolution observation taken by Galileo during an Io encounter on November 26, 1999. The northern and southern ends of the valley are cutoff by the northern margin of the observation and the dusk terminator
, so Tawhaki could be longer than the measured length. The valley was formally named
Tawhaki Vallis by the International Astronomical Union
in 2006 after the nearby volcano, Tawhaki Patera
, and the Māori
lightning god, Tāwhaki
.
Analysis of the topography of Tawhaki Vallis shows that it is likely a lava channel
, eroded into the Media Regio plain by thermal erosion. The channel is braided
, with high-standing islands in the middle of the channel. Changes in channel width are likely due to differences in the topography or substrate properties of the plains. Because the floor of the channel is lower than the surrounding plains, lava
that once flowed through the channel carved it through thermal erosion, rather than constructed from cooled lava. The theory that Tawhaki Vallis is a lava channel rather than a flow is also supported by the lack of levees on either side of the channel. This would require the lava that flowed through to be insulated from radiative
and conductive cooling along the 200-km long channel. However, the flat floor of the channel and the lack of pit crater chains nearby would also preclude the possibility that Tawhaki Vallis is a collapsed lava tube
, like Hadley Rille on the Moon
. Depending on the composition of the lava and the substrate, Tawhaki Vallis may have formed over a period of 400-600 days (for ultramafic lava flowing over ultramafic plains), 10-60 days (for sulfur
lava flow over sulfur plains), or hours to a few days when a high-temperature lava flows over a substrate with a much cooler melting point, such as ultramafic lava over plains composed primarily of sulfur. Considering the need to keep the lava liquid enough to flow over these long distances and typical duration of eruptions that could carve a channel like this, the latter possibility (high-temperature lava over a surface with a cooler melting temperature) is considered the most likely.
Similar channels to Tawhaki Vallis have also been observed near Zamama and Emakong Patera. Those channels are clearly associated with their respective volcano, but based on the images available, it is not known if an eruption at Tawhaki Patera was responsible for the formation of Tawhaki Vallis.
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 in the equatorial plains of western Media Regio at 0.5°N 72.8°W. The valley is 190 kilometers long, 0.5 to 6 km wide, and 40 to 65 meters deep. Due to the shallow depth and lack of brightness or color variations associated with it, Tawhaki Vallis was seen in only a single, high spatial resolution observation taken by Galileo during an Io encounter on November 26, 1999. The northern and southern ends of the valley are cutoff by the northern margin of the observation and the dusk terminator
Terminator (solar)
A terminator, twilight zone or "grey line" is a moving line that separates the illuminated day side and the dark night side of a planetary body...
, so Tawhaki could be longer than the measured length. The valley was 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...
Tawhaki Vallis by 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...
in 2006 after the nearby volcano, Tawhaki Patera
Tawhaki Patera
Tawhaki Patera is an active volcano on Jupiter's moon Io. It is located on Io's leading hemisphere at within the equatorial plains of western Media Regio. Tawhaki is an Ionian patera, a type of volcanic crater similar to a caldera, wide and deep....
, and the Māori
Maori mythology
Māori mythology and Māori traditions are the two major categories into which the legends of the Māori of New Zealand may usefully be divided...
lightning god, Tāwhaki
Tāwhaki
In Māori mythology, Tāwhaki is a semi-supernatural being associated with lightning and thunder.-Genealogy:The genealogy of Tāwhaki varies somewhat in different accounts. In general, Tāwhaki is a grandson of Whaitiri, a cannibalistic goddess who marries the mortal Kaitangata , thinking that he...
.
Analysis of the topography of Tawhaki Vallis shows that it is likely a lava channel
Lava channel
A lava channel is a stream of fluid lava contained within marginal zones of static lava or levees. The initial channel may not contain levees per se, until the parental flow solidifies over what develops into the channel and creates simple levees. This initial levee allows for the building of a...
, eroded into the Media Regio plain by thermal erosion. The channel is braided
Braided river
A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars or, in British usage, aits or eyots. Braided streams occur in rivers with high slope and/or large sediment load...
, with high-standing islands in the middle of the channel. Changes in channel width are likely due to differences in the topography or substrate properties of the plains. Because the floor of the channel is lower than the surrounding plains, lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
that once flowed through the channel carved it through thermal erosion, rather than constructed from cooled lava. The theory that Tawhaki Vallis is a lava channel rather than a flow is also supported by the lack of levees on either side of the channel. This would require the lava that flowed through to be insulated from radiative
Radiative cooling
Radiative cooling is the process by which a body loses heat by thermal radiation.- Earth's energy budget :In the case of the earth-atmosphere system it refers to the process by which long-wave radiation is emitted to balance the absorption of short-wave energy from the sun.The exact process by...
and conductive cooling along the 200-km long channel. However, the flat floor of the channel and the lack of pit crater chains nearby would also preclude the possibility that Tawhaki Vallis is a collapsed lava tube
Lava tube
Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like...
, like Hadley Rille on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. Depending on the composition of the lava and the substrate, Tawhaki Vallis may have formed over a period of 400-600 days (for ultramafic lava flowing over ultramafic plains), 10-60 days (for 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...
lava flow over sulfur plains), or hours to a few days when a high-temperature lava flows over a substrate with a much cooler melting point, such as ultramafic lava over plains composed primarily of sulfur. Considering the need to keep the lava liquid enough to flow over these long distances and typical duration of eruptions that could carve a channel like this, the latter possibility (high-temperature lava over a surface with a cooler melting temperature) is considered the most likely.
Similar channels to Tawhaki Vallis have also been observed near Zamama and Emakong Patera. Those channels are clearly associated with their respective volcano, but based on the images available, it is not known if an eruption at Tawhaki Patera was responsible for the formation of Tawhaki Vallis.