With a veritable army of robots exploring Mars, we’re becoming familiar with our nearest neighbor. With upcoming missions like Europa Clipper and JUICE, Jupiter and its moons will be less mysterious, too. But what of the outer planets like Uranus? According to a new NASA analysis, there may be just as much to see out there. Scientists have combed through what little up-close data we have on Uranus and its moons, determining four of those moons could contain subsurface oceans.
Uranus has been explored very little, and not just because it invites jokes. Uranus is more than three times as far from Earth as Jupiter, and it will take the ESA’s JUICE mission eight years to reach the solar system’s largest planet. Only one spacecraft has ever visited Uranus: Voyager 2 in 1985 (see above). After this encounter, Voyager 2 visited Neptune and then followed Voyager 1 (which skipped Uranus and Neptune) on a trajectory out of the solar system.
While that data is decades old, we’ve learned much about Jupiter, Saturn, and their moons from more recent missions. This led NASA scientists to re-analyze the Voyager 2 data on Uranus, which has at least 27 moons. The research, which has been published in the Journal of Geophysical Research, focused on the five largest moons of Uranus: Ariel, Umbriel, Titania, Oberon, and Miranda. Unlike Jupiter, gravitational tidal forces from Uranus aren’t strong enough to supply substantial heat, but the research shows some of these moons could still have oceans.
The work combined the Voyager 2 data with ground-based observations and additional findings from deep space probes Galileo, Cassini, Dawn, and New Horizons. The team created models to predict the conditions on the moons of Uranus, gauging how porous the surfaces are. The findings suggest that some of these moons are sufficiently insulated to bottle up their meager internal warmth.
Previously, scientists suspected that Titania, the largest with a 980-mile (1,580-kilometer) diameter, would remain warm from radioactive decay. But now NASA thinks the four largest moons are in the same group. Only Miranda (270 miles in diameter) was deemed too small to retain internal heat. Although, Miranda does show some surface remodeling, which could mean it had an internal ocean at some point in the recent past.
The study notes that the largest moons, Titania and Oberon, may even have enough heat to make the internal ocean habitable by Earth standards. Plus, the likely presence of ammonia, chlorides, and salt could keep water liquid at lower temperatures. To test these hypotheses, someone is going to have to send a spacecraft all the way out there. A recent National Academies of Sciences survey called for the exploration of Uranus, presumably not as a joke. NASA is considering a “Uranus Orbiter and Probe” project to launch sometime in the next ten years.