The Worst Part of Losing Cassini Is That It Has No Replacement
It's a lot lonelier out there in the solar system today—and it will be for a while.
NASA/JPL-Caltech/Space Science Institute
Cassini is no more. In the early hours of the morning, the long-lived spacecraft plunged into Saturn (intentionally) and broke apart, ending its 13-year run of exploring the sixth planet and it moons. Now the outer solar system is a lonelier place—and NASA is a decade out from having another visitor.
The Juno spacecraft at Jupiter set to crash into that world next year. Everything else out beyond the asteroid belt is hastily departing, too. In 2019, the New Horizons probe the captured Pluto will turn its attention to a small, primitive body called 2014 MU69 on its way out of the solar system. By 2025, our intrepid senior citizen space probes, Voyager 1 and 2, will be too weak to send back any data to Earth. The longest-traveled human-made objects will go quiet after nearly 50 years in space.
And then? Well, there's a gap. Despite everything Cassini discovered, the plucky explorer has no direct Saturn successor, and the outlook isn't great for the rest of the region.
The Europa Clipper—a mission to explore Jupiter's icy moon that might be the best place to look for life—may launch in 2022, but that date hinges on the success of the Space Launch System, NASA's enormous and yet-to-be-tested rocket that has had its share of problems. If everything works, the clipper could arrive within two years of launch. But if it has to use an ordinary United Launch Alliance Atlas V rocket instead, then that journey could take six years, meaning it wouldn't arrive until 2028.
Elsewhere, there's the possible 2021 launch of the Lucy spacecraft, which would travel among a group of asteroids that follow behind (but don't orbit) Jupiter. The European Space Agency has one planned outer solar system mission: the Jupiter Icy Moons Explorer, set to launch the same year as the Europa Clipper. It wouldn't arrive for eight years. As far as Saturn, Uranus, and Neptune are concerned, there are hopes and dreams but not official plans on the books just yet.
Such space missions take years and years of planning. So if you want to understand why there's no follow-up to an amazing mission like Cassini, you can look back to NASA's attitudes decades ago. In the 1990s, for example, NASA under then-administrator Daniel Goldin moved towards a "faster, cheaper, better" approach that largely focused in on Mars, de-emphasizing outer solar system exploration. That approach led to the excellent rovers that have explored the Red Planet, but on the flip side of that coin, Goldin nearly cancelled Cassini prior to launch despite more than a decade of development.
It was a major shift in focus for NASA's planetary science. Up until Cassini, there had been a continuous clip of outer solar system missions. The Pioneer 10 and 11 probes launched in 1972 and performed flybys of Jupiter and Saturn, and the Voyager program followed five years later. While the 1986 Challenger disaster set back many NASA missions, Cassini and Galileo (which visited Jupiter in 1994) were both well under way at the time. After the Voyager flybys of Uranus and Neptune, there were talks of sending Cassini-like probes to each. Such talk virtually disappeared in the 1990s. The New Horizons mission team fought hard to bring the Pluto mission to life after experiencing setback after setback.
This isn't to say NASA isn't planning some cool new missions. The tennis court-sized James Webb Space Telescope will blow away the already impressive Hubble Space Telescope. Asteroid exploration is about to experience a major boon: Lucy will be joined by the already-launched OSIRIS-REx mission, and NASA will send a probe to the protoplanet core Psyche. The Mars InSight lander will drill into Mars looking for present seismic activity, and the Mars 2020 rover will improve on the work of Curiosity and Opportunity. And NASA will send the Parker Solar Probe into the Sun, which is metal as hell.
An image of the most volatile and long-lasting lightning storm that Cassini saw during its stay at Saturn, taken March 6, 2011.
But if looking back on Cassini's major discoveries at Saturn, Titan, and Enceladus have left you thirsty for more, we have some bad news: That thirst is going to go unquenched for a while. Talks of Uranus and Neptune missions are tentative at best. The best hope for Saturn now comes from NASA's New Frontiers program, which looks for excellent medium-cost missions has spawned spacecraft including Jupiter's Juno and Pluto's New Horizons. This round of New Frontiers missions must launch by 2024, and there are two Enceladus proposals, a Titan proposal, and a Saturn atmospheric probe under consideration. We may hear word about those proposals by the end of the year
"Hang tight, we're going through the evaluations now and we'll be announcing at the end of the year what some of the finalists will be," Jim Green, NASA Planetary Science Director, said at the Cassini press conference Friday morning.
Out in the far reaches of the solar system, there are hundreds of worlds beckoning visitations. The quartet of giant gas planets have 168 confirmed moons, and of those, we have yet to learn much about the 29 moons of Uranus or 12 moons of Neptune. Neptune's largest moon, Triton, is a backwards-orbiting captured Kuiper Belt object. It has geysers and an ocean, and is a patchwork world half cut with rock and ice. Uranus' moon Miranda has 6-mile cliff drop-offs—imagine a daring Death Star run through that treacherous terrain. Ariel may have had recent geologic activity, giving us a chance to see a world possibly just past its ocean moon phase. Umbriel is a dark world cut through with patches of bright ice and is battered by meteor bombardment. Titania, a fairly large moon, may have an ocean, as may its smaller sibling Oberon.
With Cassini gone, Juno on its own march toward destruction, and the outer solar system probes losing power by 2026, Cassini may be a sad ending to the 40+ year book on the outer solar system exploration. The rest is just slowly fading epilogue.
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