The moons of Uranus invite plans for a NASA orbiter mission
Uranus is a strange world, knocked on its side and with a distorted magnetic field. His months are perhaps even stranger.
Earlier this year, the US National Academies of Sciences, Engineering and Medicine recommended where the next flagship mission in planetary science should go — one costing perhaps $4 billion Uranus, with a launch for the 2030s. Such a mission would be the second to peer into the Uranian system, only the next Voyager 2‘s 1986 flyover; it would be the first spacecraft to stay in the neighborhood for an extended period of time. And while the ice giant’s atmosphere and interior would be key priorities for the mission, there’s more to the picture.
“In terms of the science questions that we can address with the orbiter and the Uranus probe, the list is really long,” said Richard Cartwright, a planetary scientist at the SETI (Search for Extraterrestrial Intelligence) Institute in California, during a presentation at the annual meeting of the Division of Planetary Sciences. of the American Astronomical Society held earlier this month. “And I’m just thinking about the moons—specifically, the big five.”
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all said, Uranus has 27 known moons. Closest to the planet itself are the moons in the inner ring, which Cartwright noted are the most densely packed system of satellites in the Solar System and may be exchanging material with the rings. The farthest, more than 2.7 million miles (4.3 million kilometers) from Uranus, are irregular moons, which orbit backwards and can be captured asteroids, according to NASA.
“There are so many open questions about the origin of the irregular satellites,” Cartwright said, noting that the mission staff could arrange for the spacecraft to fly past one as it approaches Uranus itself. “We don’t know much about these guys.”
But the five remaining moons, called the classic moons, are where the spacecraft could really shine. These are moons large enough to have been observed by astronomers Earth until 1950
Even the smallest and last observed of these moons, Miranda, which is about 500 km wide, embodies the mysteries surrounding the Uranian moons. “Miranda is really weird,” Cartwright said.
Voyager 2 flyby images show geological features that are difficult to decipher, he noted. Miranda has canyons 12 times deeper than Earth’s Grand Canyon, according to NASA, and the moon’s surface is unusually thick. Miranda has three large “corona” regions unlike anything scientists have seen, and boasts volcanoes that erupt slushy icy “lava”.
“There are craters that look like they’re filled with something, and then there are craters that don’t look like they’re filled with something, and in many cases these craters are right next to each other,” Cartwright said. “So something really interesting happened in Miranda’s geological past, maybe more than once.”
Miranda may be the oddest of the classic moons, but it’s in good company.
Ariel appears to have the freshest surfaces of the five classic moons. Umbriel has the oldest and darkest. Umbriel and the two largest, Titania and Oberon, were barely glimpsed by Voyager 2, but all four of the largest moons may have oceans buried beneath their icy crusts, perhaps even spitting plumes of water into space.
“Clearly we need better coverage of these moons,” Cartwright said, specifically pointing to their northern hemispheres, which Voyager 2 couldn’t see at all. Other than that, Voyager 2 only saw a snapshot, one taken while the Southern Hemisphere was in spring.
Much of the work Cartwright envisions on these worlds could be done with instruments that the Uranus orbiter would carry regardless, such as its cameras. But he also encouraged mission planners to consider adding a dust analyzer that could identify compounds based on their weight as an instrument that would be particularly valuable in understanding Uranus’ moons.
“We could actually collect the material that is ejected from the surfaces of these moons, the dust grains, and then clean it up with a dust analyzer and characterize the composition,” he said.
There is still time to propose instruments for the spacecraft. NASA said it could begin early studies about what the mission might look like in the coming year. However, Cartwright encouraged scientists not to linger.
“It’s important that we start this mission as soon as possible so that we can get that window to help Jupiter’s gravity, hit that window between 2030 and 2034 so that we can get to Uranus faster, before the system returns to the southern spring of 2050 . year,” he said.
Email Meghan Bartels at [email protected] or follow her on Twitter @meghanbartels. Follow us on Twitter @Spacedotcom and further Facebook.
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