With Possible Liquid Oceans on Moons of Uranus, Mission Funding May Soon Follow

The astronautics community has long hoped for a flagship mission to Uranus. And while many factors remain up in the air, recent models suggesting that the moons of the distant gas giant could harbor liquid oceans could bolster their cause. In the meantime, a workshop this summer may provide some hints of NASA’s priorities for future missions.

In short, a new peer-reviewed study in the Journal of Geophysical Research suggests that four of the largest moons of Uranus may have an ocean layer underneath their ice crusts and below their cores. To keep these oceans liquid, the study suggests Ariel, Umbriel, Titania, and Oberon may be able to generate internal heat through radioactive decay. Each moon also has enough insulation (through its ice layer and other means) to slow the loss of heat to space.

The work, however, is based upon a computer model as well as reanalyzed NASA data from Voyager 2’s brief flyby of the system in 1985-86 (as the planet was visible to the spacecraft starting in November 1985, ahead of the January 1986 flyby.) That said, a peer-reviewed study based on Voyager 2 radiation data published earlier this year in Geophysical Research Letters suggests Ariel and/or Miranda may have active oceans releasing materials into space.

While Uranus has been studied many times from afar since the 1980s, including with the top-tier W.M. Keck Observatory and the Hubble Space Telescope, a difficulty arises: No mission has journeyed near that planet for nearly 40 years. None is currently manifested to go, either, which is where the discussions for the decadal survey come in.

Uranus was identified as the top priority by scientists in the 2022 National Academies’ “Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032.” On an interesting note, however, there is a proposed mission to Uranus in the report, but it’s focused on learning about the origins of the planet and its moons — not necessarily the astrobiology.

The mission “will deliver an in-situ atmospheric probe and conduct a multi-year orbital tour that will transform our knowledge of ice giants in general and the Uranian system in particular,” the description of the mission reads in the report. Later estimates have pegged the mission to be at least a $4 billion effort; by comparison, Mars Perseverance (a part of NASA’s Mars Exploration Program), was close to $3 billion.

Some efforts have been brought forward to reduce the cost of a Uranus mission. In 2022, a paper published in The Planetary Science Journal led by Ian Cohen, a space scientist at Johns Hopkins University Applied Physics Laboratory, argued that a New Frontiers-class orbiter could provide a “lower-cost, potentially faster-turnaround mission” than the Uranus Flagship mission currently being proposed.

Regardless of mission cost, Cohen told SpaceRef it would be valuable to have a survey mission out in that system ahead of proposing any landing mission, as it is hard to predict what is out there.

“I think the first step — and something that the Uranus orbiter mission has talked about doing — is trying to use the instruments, particularly the lidar and the plasma instruments, to try to figure out whether or not there is in fact an ocean … before we start jumping to what could the ocean be like,” said Cohen, who also led the Voyager 2 radiation paper studying oceans at Ariel and Miranda.

For now, the flagship is what the community is pursuing at Uranus, should the funding become available. Goals of that mission will include examining the planet’s origin, as well as analyzing its interior, atmosphere, magnetosphere, and satellites and rings. The earliest optimal launch opportunities would be in 2031 and 2032, using Jupiter’s gravity to shorten how long it would take to fly out there, but other options are available at least through 2038.

Kevin Hand, deputy project scientist for Europa at NASA’s Jet Propulsion Laboratory, told SpaceRef that instrument design for such a mission could take into account the new findings, however, to gather in-situ evidence for oceans at the four moons during flybys. The instruments could potentially be based upon successful missions that have reached Jupiter (Galileo and Juno) and Saturn (Cassini), along with the Europa Clipper that is currently in the design phases.

“That may be able to reveal things like oceanic salts on the surface,” Hand said of the Uranus mission. “Perhaps we could have a microwave radiometer that can tell us about the icy surface, or even an ice-penetrating radar. These are all tools that could be useful in this investigation of whether or not there are in fact oceans beneath the icy shells of these worlds.”

Hand added that the radioactivity that perhaps may be fueling the Uranian moons’ oceans — which he said comes from “the abundance of heavy elements during the formation of worlds,” presents a third possibility for keeping oceans liquid in our solar system alone. The other two are proximity to the sun, such as what we see with Earth, and tidal energy like what is present at Europa, near the massive Jupiter.

The Uranus Flagship 2023 workshop

More information on mission design may be coming soon, informed by the new study. In July, the Lunar and Planetary Institute (a part of the Universities Space Research Association) will host the “Uranus Flagship 2023” workshop in Pasadena, California, to discuss potential instrument concepts and scientific investigations for the planet. It is available both virtually and in-person.

“This workshop will advance planning for the Uranus Orbiter and Probe mission called for by the recently released Planetary Science and Astrobiology Decadal Survey,” the description for the three-day event reads. No information is yet available on follow-ups, such as a report, but most such sessions do have public communications of some sort following the panels.

Workshop sessions will fall under three broad categories concerning science on “origins, evolution, and workings of the Uranian system”, along with instrument concepts and requirements, and mission design. Diversity will also be brought forward in a panel discussion.

Cohen, cautioning he is not speaking for NASA, said the workshop will likely take into account not only the new observations, but how to fit the Uranus orbiter in with other agency-wide priorities such as astrophysics or heliophysics research.

“We’re really trying to look into cross-disciplinary approaches … investigations and technologies that could be added to the Europa mission to make it more impactful across the broader science mission directorate at NASA,” Cohen added of community discussions surrounding a potential Uranus mission.

The decadal survey, incidentally, had recommended meaningful funding begin for a Uranus mission in fiscal year 2024; since that spacecraft is not on the current budget manifest, planning could shift to a less ambitious 2028 timeline also available in decadal budget planning, Cohen said.