The uranium satellite Miranda may contain an ocean of liquid water, according to a team of researchers who recently mapped the satellite’s surface and modeled tidal phenomena on it.
The team published their research earlier this month in the journal Planetary Science Journal, suggesting the “likely existence” of an ocean at least 100 kilometers (62 miles) thick on Miranda over the past 100-500 million years. Although researchers do not believe such a deep body of water still exists, liquid water could remain beneath the moon’s surface, according to one of the researchers from the Johns Hopkins Applied Physics Laboratory. If Miranda were completely frozen, the team believes that certain cracks would appear on the lunar surface, indicating the expansion of the frozen ocean inside. Based on the analysis of the available images, the researchers found that there are no such cracks.
“Finding evidence of an ocean inside an object as small as Miranda is incredibly surprising,” said Tom Nordheim, a planetary scientist at the lab and co-author of the recent paper, in a lab press release. “It helps build the story that some of these moons of Uranus could be really interesting – that there could be multiple ocean worlds around one of the most distant planets in our solar system, which is both exciting and bizarre,” Nordheim added.
The seventh planet from the Sun is often the butt of jokes, but it remains a fascinating place for planetary scientists. In 2022, the National Academies of Sciences, Engineering, and Medicine made Uranus research a top priority for the decade. And rightly so: Uranus is an oddball among worlds, with a strange tilt, a large white spot, extreme seasons, and an infrared aurora in its gaseous atmosphere. While we often think of Saturn as the ringed planet in the solar system, images from the Webb Space Telescope released last year showed the luminous rings around Uranus in more vivid detail than ever before.
And that’s not to mention Uranus’ nearly 30 satellites. Earlier this year, another team of astronomers discovered a new satellite orbiting the planet for the first time in 20 years. This satellite is only five miles (eight kilometers) wide and has been orbiting the planet for almost two years. Although it doesn’t have a name yet, it will eventually be given a Shakespearean name, just like its rocky brethren surrounding Uranus (besides Miranda, there’s Rosalind, Puck, Belinda, Desdemona, Cressida, Juliet… I could go on).
But this story is about Miranda. In the top image, you see one of the few up-close images of the icy moon taken by NASA’s Voyager 2 in 1986, when that intrepid spacecraft was venturing beyond the solar system. The image shows Miranda’s uneven surface, covered with grooves and craters that scientists believe were formed by tidal forces on the moon and the heating inside it.
In a recent study, the team modeled the moon’s interior based on features of its exterior; essentially, the team analyzed evidence of stress and shear on Miranda’s surface to infer internal forces that may have shaped the moon’s appearance. In the article, the authors write that orbital changes due to gravitational interactions between Miranda and other moons of Uranus may have caused a pulse of heat inside the moon, which created a deep ocean at some point in the distant past.
The team also wrote that the crust, approximately 8 miles (30 kilometers) thick, “also suggests” a “subterranean ocean of liquid water” 62 miles (100 kilometers) thick. By comparison, the Mariana Trench, the deepest point in the world’s oceans, is only 6.83 miles (11 km) deep. While such a deep ocean likely no longer exists, the idea that it was once there – and the fact that a thin ocean could exist – remains valid.
“Such a thick ocean could have made Miranda very similar to Enceladus,” the team explains, “and potentially habitable in the geologically recent past.
Astrobiology – the search for life beyond our planet – is one of the most exciting areas of space exploration. It is an integral part of what we do in space, from launching rovers to Mars to photographing distant exoplanets orbiting their own stars light years away. Despite some of these distant goals, some astrobiologists believe that our best chances for life beyond Earth are relatively close at hand-in the underground oceans of icy moons like Europa, Ganymede, Enceladus, and Miranda.
It will be years before any space agency can send a probe to Miranda, but some icy discoveries may be just around the corner. The Jupiter ICy moons Explorer (JUICE) and Europa Clipper missions are now headed to the Jovian system to explore Jupiter’s icy moons in more detail. What they find may provide a useful context for a better understanding of Miranda, whose interior may yet reveal a fascinating new world.
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