In the past few decades, planetary scientists have been constantly increasing the number of moons in the solar system that have, or perhaps had, oceans deep inside them. Such moons (for example, Europa or Enceladus) in most cases have been associated with the gas giants Jupiter and Saturn.
However, in recent times, the focus of the planetary scientists began shifting much more towards the ice giant Uranus, the most frigid of all planets in the solar system. And at present, new studies of the images of Miranda taken by the Voyager 2 probe indicate that this small icy satellite of Uranus used to have a vast liquid water ocean beneath its icy crust.
What is more, traces of that ocean may still be present on Miranda today.
Below is a photo showing not just Miranda, but all of the major moons of Uranus.
Voyager 2 spacecraft flew by Miranda in 1986 and photographed its south polar regions. The obtained pictures showed the various features on the moon's surface, such as grooved terrain, rough scarps and cratered regions.
Tom Nordheim, a planetary scientist at Johns Hopkins University Applied Physics Laboratory (APL) among other researchers, sought to account for the peculiar geology of Miranda by justification of its tectonics, namely, suggesting what internal structures allow present-day appearance of the satellite.
The group had first completed the outline of cracks, ridges and other surface features of the satellite as imaged by Voyager 2, and then devised a numerical simulation to investigate which of the hypothesized structural configurations could account for the distribution of stresses on the surface of the moon.
The computer model incorporated an internal composition that produced the best fit between stress models at the surface and the geological surface of the moon, indicating that there was an ocean under the surface of Miranda approximately between 100 and 500 million years ago. Their simulations theorized that the ocean may have reached a size of up to 100 kilometers (62 miles) below the surface ice that was 30 kilometers thick, and had an ice layer of 30 kilometers above it.
Miranda has a mere radius of 146 miles (235 kilometers), which most implies that the ocean would have comprised nearly half of the entire volume of the moon. This also indicates that the presence of such an ocean is improbable. “To find evidence of an ocean inside a small object like Miranda is incredibly surprising,” Nordheim said commenting on the findings of the study.
“It helps build on the story that some of these moons at Uranus may be really interesting — that there may be several ocean worlds around one of the most distant planets in our solar system, which is both exciting and bizarre,” he went on to say.
The researchers posit that tidal heating between Miranda and its sister moons was necessary in maintaining the ocean within or even below its surface warm. Could also the gravitational heating produced by the stretching and squashing of Miranda, enhanced by the orbital relations with other moons previously, had produced heat sufficient to prevent her from icing up?
Additionally, the moons of Jupiter, Io and Europa, share a 2:1 resonance (for every two orbits made by Io around Jupiter, Europa completes one), which produces sufficient tidal forces to allow for an ocean located underneath the crust of Europa.
At last, one of the other Uranian moons brought Miranda out of a state of synchronicity, which effectively removed the agent that heated the moon’s interior. However, researchers do not believe that Miranda is completely solidified simply as it should have bulged, leaving distinct fissure marks on the surface.
"We won't know for sure that it even has an ocean until we go back and collect more data," Nordheim says.
"We're squeezing the last bit of science we can from Voyager 2's images. For now, we're excited by the possibilities and eager to return to study Uranus and its potential ocean moons in depth."
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