Ruach Planitia
A probable cryolava lake on Neptune's moon Triton.
Ruach Planitia is a roughly circular, flat plain on Neptune’s moon Triton, likely a frozen cryolava lake. It lies in Triton’s northern hemisphere, within Monad Regio, bordering the cryovolcanic plains of Cipango Planum to the east and Tuonela Planitia to the west. It is among the youngest and flattest features seen on Triton, along with the moon’s three other walled plains.
The feature was first spotted by Voyager 2 during its flyby of the Neptune system on 25 August 1989. The International Astronomical Union approved the name Ruach Planitia in 1991, after the legendary French island of Ruach.
The plain is quasi-circular, about 175–180 km across. Its floor sits roughly 200 meters lower than the surrounding plains, enclosed by a scarp that varies from 40 to 250 meters in height. Most of the plain is ringed by a single scarp, but on the east side the scarp splits into two, creating a terraced profile. The floor is generally flat but may be subtly warped; whether these undulations are real or artifacts of Voyager 2’s limited elevation data is unclear. The central area is more topographically varied, featuring a large central pit—Dilolo Patera—nearly 10 km wide and about 350 m deep. This pit is surrounded by a network of smaller pits, linear troughs, and scarps. This pit cluster resembles those found in Triton’s other three walled plains, each having a single cluster with the largest pit at the center. Both Ruach Planitia and nearby Tuonela Planitia cut into the surrounding cantaloupe terrain, and Ruach Planitia also cuts into the western parts of Cipango Planum.
The terraced appearance of Ruach Planitia is similar to that of large terrestrial volcanic calderas. As with such calderas, eruptions here may have occurred in stages: an early explosive phase involving high-viscosity or high-volatility cryolava (water-dominated material analogous to silicate lava) that formed the terraced walls, followed by a later effusive phase that created the flat floor. However, the crenulated walls do not clearly indicate collapse; instead, they resemble eroded shorelines on Earth. The multiple terraces on the eastern side may result from compositional differences in Triton’s crustal layers, some richer in volatiles than others. The flat floor suggests fluid cryolava later filled the depression, with the pits around Dilolo Patera acting as central vents for eruptions.
Quick Facts
- Location
- Monad Regio, Triton
- Depth
- ~200 m106
- Diameter
- ~175 km869
- Discoverer
- Voyager 2
- Eponym
- Isle of Ruach
Facts from the source article.
Lore & Background
Ruach Planitia was discovered alongside Triton's other surface features by the Voyager 2 spacecraft during its flyby of the Neptune system on 25 August 1989. The name Ruach Planitia was approved by the International Astronomical Union (IAU) in 1991; it is named after the legendary French isle of Ruach. The plain is quasi-circular, with its floor depressed by about 200 meters relative to the surrounding plains and surrounded by a bounding scarp that ranges in height between 40 and 250 meters. On its east side, the scarp appears to separate into two, giving a terraced profile. The floor is generally flat but may be subtly warped, though whether these are artifacts or true elevation features is uncertain given the limitations of Voyager 2 elevation data. The central region contains a large central pit—Dilolo Patera—nearly 10 km wide and roughly 350 m deep, surrounded by a network of smaller pits, linear troughs, and scarps. This pit cluster is similar to those found within the other three walled plains of Triton. Both Ruach Planitia and nearby Tuonela Planitia cut into the surrounding cantaloupe terrain, and Ruach Planitia cuts into the western regions of Cipango Planum.
Reader's Guide
Ruach Planitia's terraced appearance resembles that of terrestrial volcanic calderas, albeit at a very large scale. As with terrestrial calderas, eruptions from Ruach Planitia may have involved several distinct stages, with an early explosive stage of high-viscosity or high-volatility cryolava (erupted water-dominated material analogous to silicate lava) forming the terraced walls, followed by a later effusive stage that formed the flat floor. However, the crenulated appearance of the walls does not appear to indicate collapse, instead resembling eroded shorelines on Earth. The multiple terraces on its eastern side may have arisen from compositional differences in different layers of Triton's crust. The flat floor suggests fluid cryolava infilled the depression, with the pits around Dilolo Patera acting as central vents. The surrounding terrain appears significantly modified by apparent glaciation, with the cliffs of both Ruach Planitia and Tuonela Planitia having been significantly eroded. The north wall of Ruach Planitia appears to have been breached in at least three sites, connecting to an apparent channel system stretching for at least ~230 km, though it extended beyond Triton's terminator into unimaged regions. It remains uncertain which direction fluids may have flowed within the channel, though tentative deposit features on the north floor may indicate material flowed into the plains. Several smaller subcircular depressions nearby to the south and southwest may be of cryovolcanic origin or from diapirism.
Did You Know?
- Its central pit, Dilolo Patera, is nearly 10 km wide and roughly 350 m deep.
- The bounding scarp around Ruach Planitia ranges in height from 40 to 250 meters.
- A channel system from its north wall stretches for at least ~230 km.
Frequently Asked Questions
What is Ruach Planitia?
Ruach Planitia is a roughly circular, flat plain on Triton, Neptune's largest moon, that scientists believe is a frozen cryolava lake. It ranks among the youngest and flattest surface features identified on the moon alongside three other walled plains.
Where exactly is Ruach Planitia located on Triton?
It sits in Triton's northern hemisphere within the larger Monad Regio region. To its east it borders the cryovolcanic plains of Cipango Planum, and to its west it meets Tuonela Planitia.
How was Ruach Planitia discovered and named?
Voyager 2 first imaged the feature during its flyby of the Neptune system on 25 August 1989. The International Astronomical Union officially approved the name Ruach Planitia in 1991, drawing from the legendary French island of Ruach.
What are the key dimensions of Ruach Planitia?
The plain spans roughly 175 to 180 km in diameter, with a floor that dips about 200 meters below the surrounding terrain and bounding scarps ranging from 40 to 250 meters in height. At its center lies Dilolo Patera, a pit nearly 10 km wide and approximately 350 m deep.
Why do scientists think Ruach Planitia is a cryolava lake?
Its extreme flatness, young appearance, and the presence of a central pit (Dilolo Patera) are consistent with a basin that once held and then froze a cryogenic lava flow. These traits distinguish it from impact craters and align it with the other walled plains on Triton interpreted as ancient cryolava deposits.
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