Apr 20, 2022 7:00 AM

Get Ready for a Decade of Uranus Jokes

In an influential report that comes out once a decade, researchers propose a space mission to Uranus and a lander to Saturn’s moon, Enceladus.

For the past couple of decades, NASA has been investing in spacecraft to conduct up-close examinations of Mercury, Venus, Mars, Jupiter, and Saturn. Now it’ll likely be Uranus’ turn.

On Tuesday, a team of planetary science and astrobiology researchers released a detailed new report called a decadal survey, which lays out research priorities for their field. Like the census, a decadal survey comes out every 10 years and has important political implications. The previous assessment by planetary scientists prioritized a Mars sample return mission and a probe to Jupiter’s moon Europa—the federal government agreed to fund those in the 2020s. This time, the researchers argue that a Uranus orbiter and probe should be considered “the highest-priority new flagship mission” that could be developed and even launched within the next decade. Their second-place choice is to search for life on Saturn’s moon Enceladus, which harbors an underground ocean, a tiny bit of which sprays out in plumes.

These new recommendations could eventually become realities too. That’s because the report, organized by the National Academies of Sciences, Engineering, and Medicine, has broad support. It’s respected by members of Congress, NASA, and the scientific community. “It’s very likely to me that the Uranus orbiter will happen. This kicks off an interesting process of morphing ideas and words into metal and technology of spacecraft that takes decades,” says Casey Dreier, the senior space policy adviser for the Planetary Society, a nonprofit research organization based in Pasadena, California, whose president served on the report’s steering committee. “We’ll be enjoying Uranus jokes for years,” he adds.

The report calls for a spacecraft that would study the ice giant’s interior and atmosphere, its magnetic field, its rings, and its many moons. If NASA has the funding and support to get started within the next couple of years, the authors write, such a probe could be launched by 2032 and swing by Jupiter for a gravity-assisted boost in speed that could help it arrive at the end of that decade. But considering the major pieces of the NASA budget pie now focused on Mars and Europa, launching such a spacecraft later in the 2030s might be more likely, Dreier says. Then the voyage itself would take the better part of a decade.

A few decades ago, Mars and Venus seemed like the obvious places to look for extraterrestrial life, since those planets might have once held liquid water on the surface, which all known life-forms need. But there may be other life-friendly spots in our neighborhood too: ocean worlds, which in our solar system are distant moons with liquid lakes or oceans, some deep underground.

The new report, titled “Origins, Worlds, and Life,” emphasizes such worlds, since they might host the alien microbes that scientists have long been hunting for. Known ocean worlds include Europa and Titan, moons of Jupiter and Saturn that NASA’s targeting with the Europa Clipper and Titan Dragonfly missions. But Enceladus, a smaller brother of Titan’s, is an ocean world in its own right, and researchers picked it as the second priority, a place to send an “orbilander,” a spacecraft that will function as both an orbiter and a lander. “It’s been Enceladus’ turn for so long. It’s been begging for us to come,” says Nathalie Cabrol, an astrobiologist and head of the Carl Sagan Center for Research at the SETI Institute in Mountain View, California, an organization focused on the search for extraterrestrial intelligence.

While Europa and Enceladus have below-ground oceans, Cabrol’s excited about the latter because it’s spewing ocean material outward in geyser-like plumes through cracks in its thick, icy crust. An orbiter might have a shot of snagging a plume sample while flying by, but a lander has a much better chance of spotting and investigating that sought-after material after it has fallen back onto the surface. High methane levels have already been detected in Enceladus’ plumes, a potential sign of life depending on what other chemicals are present.

Scientists consider five of Uranus’ 27 known moons to be candidate ocean worlds, as well: Miranda, Ariel, Oberon, Titania, and Umbriel (the only one not named after a Shakespearean character). But there’s a dearth of data from the Uranus system, and much of the information available dates back to the Voyager 2 flyby in 1986. Scientists got a more detailed perspective of Jupiter and Saturn once the Juno and Cassini spacecraft visited in 2004 and 2016, respectively, but those missions did not include Uranus. Cabrol applauds the focus on the Uranus system, which is usually forgotten, she says.

Considering the diversity of ocean worlds studied so far, combined with fascinating geological activity on the dwarf planet Pluto, revealed by the New Horizons spacecraft in 2015, it makes sense to zoom in on other worlds too, Cabrol argues. “The solar system is such a beautiful natural lab. It’s like cooking with different ingredients and different temperatures, you come up with very different things,” she says.

Nevertheless, with so many popular destinations, there are always disagreements about where to direct spacecraft resources. Some researchers in the field have previously pushed for different candidates and missions. “The emphasis on the outer solar system is good to see, and the Uranus mission will be useful, but our top priority was Triton,” says Amanda Hendrix, an astronomer at the Planetary Science Institute in Tucson, Arizona, and lead author of “The NASA Roadmap to Ocean Worlds” report in 2019, which informed the new survey. She and her team highly ranked the Neptune moon and candidate ocean world for further study ahead of Uranus and its moons. But the National Academies researchers rated it lower, citing the “lack of demonstrated viable trajectories to Neptune for a launch within the decade” and the need for solar-electric propulsion if neither NASA’s Space Launch System nor a Jupiter gravity assist are available to help it get there.

The decadal report included a matrix through which the authors weighed 12 science questions for a variety of proposed space missions. Missions that could inform scholars about many areas of science, such as about the history of the solar system and the origins of life, were given greater weight. Dreier puts it this way: “At the end of the day, what the decadal is saying is: ‘Given these resources, where do you put your dollars in a way that maximizes your science return?’”

The report also recommends investing more in planetary defense, or making sure that near-Earth asteroids and comets won’t end up on a collision course with our own world. Planetary scientists naturally don’t want a Don’t Look Up situation, and that means cataloging and following the orbits of as many objects as possible. NASA’s already working on monitoring near-Earth objects, and this fall it will test whether it’s possible to deflect an asteroid by crashing a spaceship into one. But the Biden administration’s proposed budget includes a cut to the NEO Surveyor, which would delay the asteroid-tracking spacecraft’s launch. With the endorsement of the decadal report, however, the mission now has the imprimatur of the scientific community, and perhaps it won’t see its budget slashed.

This isn’t the only advisory report NASA has to take into consideration when allocating money. The better-known Astrophysics and Astronomy Decadal Survey, which was released in November, called for projects aimed outside the solar system, like one focused on habitable exoplanets and another on evolving galaxies.

The goals planetary scientists laid out in the new report are much more sweeping than those of previous decadal surveys—and they'll cost more too. “At the end of the day," Dreier says, “the recommendations won’t mean squat if you don’t have funding to enable it.”