Should NASA send a mission to explore Uranus and its moons? It’s been on NASA’s “to do” list for the past decade, and scientists are warning that if a spacecraft doesn’t launch soon, the next best window will be the 2090s.
We’ll find out soon. April 19, 2022 is due for recommendations from the Decadal Survey for Planetary Science and Astrobiology, a report compiled by the National Academy of Sciences that will set NASA’s priorities for the next 10 years.
Although it is expected to give the green light to a Mars sample-return mission – much of which is already being planned by NASA – there is a reasonable chance it will also direct the space agency to use one of the Solar System’s “ice giant” planets, Neptune, to investigate and Uranus. After all, a mission to Uranus 10 years ago was the third highest priority flagship mission. Nothing has been done.
Which planet should NASA prioritize? The advantages and disadvantages of missions to the two ice giant planets can be summarized as follows:
- The seventh planet Uranus has five moons that could be “sea worlds” that could harbor life.
- The eighth planet Neptune has a moon called Triton, which is believed to be a captured dwarf planet – much like Pluto – so a mission would represent a two-for-one deal.
The case for Uranus, the third largest planet in our solar system in a slow 84 Earth-year orbit around the Sun, is made in two proposals currently under consideration by the Decadal Survey:Search for Uranus to explore theories of the solar system (QUEST) and A New Frontiers class mission for the Uranian system.
“Uranus is the only known example in our solar system of what an ice giant system would look like,” said Erin Leonard of NASA’s Jet Propulsion Laboratory and lead author of the two proposals. “It’s the only place we have moons around an ice giant that’s always been where there aren’t invaders from the Kuiper Belt who were then trapped, which is Triton.”
Leonard’s proposals call for New Frontiers missions — costing no more than $900 million, about a third the cost of a full-blown flagship mission — to send an orbiter to Uranus that would launch in 2032 and arrive at Uranus in 2045.
The Juno-style QUEST orbiter would study Uranus’ oddly shaped and chaotic magnetic field and its extreme axial tilt (Uranus orbiting on its side). Keyword updates to longstanding planet-forming theories and valuable data on icy planets, the most common in our galaxy.
QUEST would also investigate why Uranus appears colder than it should be.
“The interesting thing about Uranus is that Voyager 2 did not detect any emission of internal heat. This is very different from the other three giant planets, which give off more heat than they receive from the sun because they’re giant compressed balls of gas,” said Dr. Kunio Sayanagi of the Hampton University School of Science. “They all have interiors with very high temperatures that are fading out, but not on Uranus. There is something interesting going on that cannot be explained in that way.”
Meanwhile, the other concept focuses on Uranus’ rings, its magnetic field, and a study – through fly-bys – of possible subsurface oceans on some of its 27 moons. There is tantalizing evidence from Voyager 2 that the innermost and largest of the moons – Miranda, Ariel, Umbriel, Titania and Oberon – may harbor subterranean oceans. They also have surfaces that appear geologically young (read: free of many craters), so appear to be geologically active.
Humanity has only visited Uranus once. A brief flyby by NASA’s Voyager 2 spacecraft on January 24, 1986 gave us our only close-up views of Uranus and discovered 10 new moons. The only other images we have of Uranus are from the Hubble Space Telescope and ground-based telescopes like Keck.
Planetary researchers are keen to take a closer look at them. A Moons of Uranus project is already scheduled for the first-ever installment of James Webb Space Telescope (JWST) scientific work later in 2022. It will spend 21 hours closely examining Ariel, Umbriel, Titania and Oberon and to look for traces of ammonia. organic molecules, carbon dioxide ice and water.
Any discoveries JWST makes will inform each mission, study them up close of course although time is of the essence. If NASA wants to send a mission, it needs gravitational assistance from Jupiter, which can only happen about once every 12 years. This will be available from 2029 to 2034.
“If the planets line up properly, we can use Jupiter to get to Uranus, which means we can launch more mass and also get there a little faster, which makes everything just a little bit cheaper,” Leonard said.
However, there is another seasonal reason why now is the time for a mission to Uranus. It is critical that a mission reach the Uranian system in the early 2040s, when the northern high latitudes of its moons are still visible. This opportunity will disappear once the system transitions into southern spring in the late 2040s and will not return until the 2090s. “We don’t want it to be a full Uranus year since Voyager was there because the whole Uranus system has tipped on its side,” Leonard said. “When we were there on Voyager, only the southern hemispheres of the moons were illuminated. We would really like to see other parts of the moons.”
There are now plans for flagship and New Frontiers missions to Uranus, but whatever the preference, such a mission must be launched between 2030 and 2032, regardless of size or cost.
Could NASA complete a mission in 10 years? “For a flagship mission, that’s pretty close, but you could do it,” Leonard said, citing the fact that flagship missions are inherently more complicated because they have more scientific instruments. “But I would say for a New Frontiers mission it’s easier to do it a little faster, but as always it’s all budget driven.”
Each mission would take 10 years to build and launch and another 13 years to get there. Either way, it will be a quarter of a century before anyone does new science on the seventh planet in the solar system.
I wish you clear skies and big eyes.