The US Decadal Survey for Planetary Science dropped today, prioritising Uranus for a flagship mission in the coming decade. I had the opportunity to talk to a number of reporters, some of the frequent questions are included below.
Here's the news from the National Academies on #PlanetaryDecadal and #Uranus: when I first read that recommendation, I feared I might be dreaming! Elation, relief, gratitude to the team that made this happen, and a little trepidation about the road ahead. https://t.co/rPVLRedgkL pic.twitter.com/Xq3cj6xzvi
— Leigh Fletcher (@LeighFletcher) April 19, 2022
What does it mean to you to have such a top recommendation for an ice-giant mission?
When I first read that recommendation, I feared I might be dreaming! Elation, relief, pride in the team that made this happen, and a little trepidation about the road ahead. Today we’re one step closer to seeing that ambitious orbital mission to an Ice Giant system that we’ve been working towards for so long.
I owe my career to the pioneers who pushed for the Cassini-Huygens mission to Saturn and Titan, and there’ll be hundreds of future scientists out there today who’ll now get the same chance, making their own discoveries in the Uranian System. I started thinking about Ice Giant exploration in 2008, ahead of the last decadal survey that ranked Uranus as a third priority after Mars and Europa. We’ve been carrying that torch – through research, white papers, mission proposals, and international meetings – on and off for 15 years (including the 2020 Royal Society meeting in London, just before the pandemic hit). The science case has only improved with time, particularly as Ice-Giant-sized worlds (or just smaller) appear commonplace in the pantheon of exoplanets. This decadal survey prioritisation is a wonderful leap forward for the outer solar system community.
When would you think, realistically, a Uranus mission would launch if NASA takes the decadal's recommendation?
There are many hurdles to come – political, financial, technical – so we’re under no illusion. However, missions to Ice Giants are dramatically improved, in terms of the mass that you can deliver to orbit around the planet, if you can borrow some of Jupiter’s energy for a gravitational slingshot. For that, Jupiter has to be in just the right place, which it will be in the early 2030s – the earliest possible slot is 2031 for a 13-year cruise to Uranus, with flexible launch opportunities for a few years after with longer cruises. That gives us around a decade to go from a paper mission to hardware in a launch faring, so there’s no time to lose.
In your opinion, is Neptune entirely off the table for a mission in the near future, given the decadal's concerns about launch options?
The case for a Neptune mission remains as strong as ever, particularly given the high interest in studying Triton as a captured KBO. Indeed, we’d learn far more about the nature of Ice Giant systems via a true comparative study. But it comes down to opportunities: a Jupiter gravity assist for Neptune is available at the end of the 2020s, a little too close for comfort for developing a flagship orbiter and probe. Whilst other trajectories exist without a Jupiter flyby, they’re not without risk and cost, and the decadal suggests that new studies of technology development for a Neptune mission are needed. The next gravity-assist window for Neptune might be under consideration for the 7th New Frontiers mission sometime in the late-2030s/early-2040s, but it’s hard to predict the state of play that far in advance.
And how might a NASA Uranus mission mesh with European contributions, given that an ESA contribution to an international mission to the ice giants was noted in the recent Voyage 2050 exercise from Europe?
I was heartened to see the Voyage-2050 recommendation of an Ice Giant mission with international partners – the same message was given in 2013 when we proposed Ice Giants as a destination for ESA’s L-class missions, and the ESA Director of Science used Ice Giants as an example of what could be done with an ESA funding uplift back in 2019. The key question now is whether there’s room in national budgets and ESA’s science programme for an ambitious partnership – I hope so, but we’ll have to wait and see! After all, the Cassini-Huygens partnership, with its clean separation of tasks and responsibilities, was cited as “a superb example of international cooperation” in this survey.
