6.05.2023
Uranus is surrounded by its four major rings and 10 of its 27 known moons in this color-added view that uses data taken by the Hubble Space Telescope in 1998. A study featuring new modeling shows that four of Uranus’ large moons likely contain internal oceans. Credit: NASA/JPL/STScI
The work is based on new modeling and explores how oceans could exist in unlikely places in our solar system.
Re-analysis of data from NASA’s Voyager spacecraft, along with new computer modeling, has led NASA scientists to conclude that four of Uranus’ largest moons likely contain an ocean layer between their cores and icy crusts. Their study is the first to detail the evolution of the interior makeup and structure of all five large moons: Ariel, Umbriel, Titania, Oberon, and Miranda. The work suggests four of the moons hold oceans that could be dozens of miles deep.
In all, at least 27 moons circle Uranus, with the four largest ranging from Ariel, at 720 miles (1,160 kilometers) across, to Titania, which is 980 miles (1,580 kilometers) across. Scientists have long thought that Titania, given its size, would be most likely to retain internal heat, caused by radioactive decay. The other moons had previously been widely considered too small to retain the heat necessary to keep an internal ocean from freezing, especially because heating created by the gravitational pull of Uranus is only a minor source of heat.
The National Academies’ 2023 Planetary Science and Astrobiology Decadal Survey prioritized exploring Uranus. In preparation for such a mission, planetary scientists are focusing on the ice giant to bolster their knowledge about the mysterious Uranus system. Published in the Journal of Geophysical Research, the new work could inform how a future mission might investigate the moons, but the paper also has implications that go beyond Uranus, said lead author Julie Castillo-Rogez of NASA’s Jet Propulsion Laboratory in Southern California.
New modeling shows that there likely is an ocean layer in four of Uranus’ major moons: Ariel, Umbriel, Titania, and Oberon. Salty – or briny – oceans lie under the ice and atop layers of water-rich rock and dry rock. Miranda is too small to retain enough heat for an ocean layer.
“When it comes to small bodies – dwarf planets and moons – planetary scientists previously have found evidence of oceans in several unlikely places, including the dwarf planets Ceres and Pluto, and Saturn’s moon Mimas,” she said. “So there are mechanisms at play that we don’t fully understand. This paper investigates what those could be and how they are relevant to the many bodies in the solar system that could be rich in water but have limited internal heat.”
The study revisited findings from NASA’s Voyager 2 flybys of Uranus in the 1980s and from ground-based observations. The authors built computer models infused with additional findings from NASA’s Galileo, Cassini, Dawn, and New Horizons (each of which discovered ocean worlds), including insights into the chemistry and the geology of Saturn’s moon Enceladus, Pluto and its moon Charon, and Ceres – all icy bodies around the same size as the Uranian moons.
What Lies Above and Beneath
The researchers used that modeling to gauge how porous the Uranian moons’ surfaces are, finding that they’re likely insulated enough to retain the internal heat that would be needed to host an ocean. In addition, they found what could be a potential heat source in the moons’ rocky mantles, which release hot liquid, and would help an ocean maintain a warm environment – a scenario that is especially likely for Titania and Oberon, where the oceans may even be warm enough to potentially support habitability.