Ceres' vanishing ice volcanoes: Dwarf planet may have had 'cryovolcanoes' millions of years ago that flattened out over time, leaving just one behind
- Researchers recently discovered a solitary ice volcano on the dwarf planet Ceres
- NASA's Dawn spacecraft discovered the cryovolcano called Ahuna Mons in 2015
- New research suggests there may have been others millions or billions of years ago, and they may have flattened out over time to become indistinguishable
Researchers recently discovered a solitary ice volcano - a cryovolcano - on the dwarf planet Ceres, but new research suggests there may have been others that slowly disappeared over millions of years.
NASA's Dawn spacecraft discovered the cryovolcano, called Ahuna Mons, in 2015, and since then the spacecraft has been capturing images and topography data to build up a clearer picture of the dwarf planet.
Researchers show there may have been cryovolcanoes other than Ahuna Mons on Ceres millions or billions of years ago, but they may have flattened out over time and become indistinguishable from the planet's surface.
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Named Ahuna Mons, the dome-shaped cryovolcano on Ceres is believed to have formed within the last 200 million years as the internal pressure of ice from below burst up through the crust
Ceres, with an orbit between mars and Jupiter, lies closer to the sun than other planets or celestial bodies where cryovolcanoes have been observed.
Its dome-shaped cryovolcano is believed to have formed relatively recently, likely within the last 200 million years.
The researchers said that Ahuna Mons' steep sides and well-defined features are usually signs of a geologically young structure - which could lead to two possibilities.
Either Ahuna Mons is alone after having formed recently.
Or, it's not alone, and some process on Ceres destroyed past cryovolcanoes - leaving Ahuna Mons solitary.
The research, accepted for publication in the journal Geophysical Research Letters, began out of curiosity as to why Ahuna Mons exists as a lone cryovolcano.
Dr Michael Sori, a researcher at the Lunar and Planetary laboratory at the University of Arizona in Tucson, and lead author of the research, said: 'Imagine if there was just one volcano on all of Earth.
'That would be puzzling.
'We think we have a very good case that there have been lots of cryovolcanoes on Ceres but they have deformed.
Because Ceres has no atmosphere, the processes that wear down volcanoes on earth, such as rain, wind and ice, can't happen on the dwarf planet.
So the research team proposed that another process - called viscous relaxation - was causing the volcanoes to disappear.
Viscous relaxation is the concept that any solid will flow given enough time.
Ahuna Mons (pictured) is believed to have formed relatively recently, likely within the last 200 million years, from pressure within the protoplanet. Pictured is the cryovolcano from above, at a width of 30 km
Ceres' mysterious mountain Ahuna Mons is seen in this mosaic of images from NASA's Dawn spacecraft. Dawn took these images from its lowest-altitude orbit
It doesn't happen with volcanoes on Earth because they're made of rock, but it does happen in glaciers.
Since Ahuna Mons is made of ice, viscous relaxation is possible.
Dr Sori said that on Ceres, viscous relaxation could be causing older cryovolcanoes to flatten out over millions of years, making them hard to see.
Ceres's location close to the sun could make the process more pronounced too.
To test their theory, the researchers created a model of Ahuna Mons to predict how fast the mountain could be flowing.
NASA's Dawn (artist's impression pictured) is the first mission to visit a dwarf planet. Earlier last year, Dawn revealed the images of the dwarf planet's craters in unprecedented detail. The spacecraft took the images near its lowest ever altitude to Ceres, at 240 miles (385 km) from the surface, in December 2015
Since the ice volcano could be made of materials other than pure water, the researchers ran the model ranging from 100 per cent water mixtures to 40 per cent mixtures.
If Ahuna Mons is made of more than 40 per cent water, viscous relaxation is possible.
At this composition, Dr Sori estimates that Ahuna Mons should be flattening out at a rate of 10 to 50 meters (30 to 160 feet) per million years.
That's enough to render cryovolcanoes unrecognizable in hundreds of millions to billions of years, suggesting there could have been other cryovolcanoes on Cere.
Dr Sori said: 'Ahuna Mons is at most 200 million years old.
'It just hasn't had time to deform.'
The researchers next want to try and identify the flattened old cryovolcanoes on Ceres.
This could help researchers better understand the history of how the dwarf planet formed.
Dr Kelsi Singer, a postdoctoral researcher who studies icy worlds at Southwest Research Institute in Boulder, Colorado, who was not involved with the research, said: 'It would be fun to check some of the other features that are potentially older domes on Ceres to see if they fit in with the theory of how the shapes should viscously evolve over time.'
'Because all of the putative cryovolcanic features on other worlds are different, I think this helps to expand our inventory of what is possible.'
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