Uranus’ moons call for plans for NASA orbiter mission
Uranus is a strange world, knocked sideways and with a warped magnetic field. Their moons can be even stranger.
Earlier this year, the US National Academies of Sciences, Engineering and Medicine recommended where the next flagship planetary science mission should go, one that will cost perhaps $4 billion Uranuswith a targeted launch in the 2030s. This mission would be the second to look at the Uranian system, only after Voyager 21986 flyover; it would be the first spacecraft to make an extended stay in the neighborhood. 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 scientific questions that we can entertain with an orbiter and a probe at Uranus, that list is very long,” said Richard Cartwright, a planetary scientist at the Search for Extraterrestrial Intelligence (SETI) 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. The moons closest to the planet itself are the inner ring moons, which Cartwright noted are the most densely packed system of satellites in the solar system and may be exchanging material with the rings. Farther away, beyond 2.7 million miles (4.3 million kilometers) from Uranus, are the irregular moons, which orbit backwards and may be captured asteroids. according to NASA.
“There are so many open questions about the origins of irregular satellites,” Cartwright said, noting that mission personnel could arrange for a spacecraft to fly past one as it approaches Uranus itself. “We don’t know much about these guys.”
But the remaining five moons, called the classic moons, are where a spacecraft could really shine. These are the moons big enough that astronomers had detected them land by 1950
Even the smallest and last of these moons, Miranda, which is about 310 miles (500 km) across, embodies the mysteries surrounding the Uranian moons. “Miranda is very strange,” Cartwright said.
Voyager 2 flyby images show geological features that are difficult to decipher, he noted. Miranda sports canyons 12 times deeper than Earth’s Grand Canyon, according to NASA, and the moon’s surface is unusually thick. Miranda is home to three large “corona” regions that are unlike anything scientists have ever seen, and boasts volcanoes that erupt “lava” of muddy ice.
“There are craters that look like they’ve been filled with something, and then craters that don’t look like they’ve been filled with something, and in many cases those craters are right next to each other,” he said. Cartwright. . “So something really interesting happened in Miranda’s geological past, maybe several times.”
Miranda may be the oddest of the classic moons, but it’s in good company.
Ariel appears to have the coolest surfaces of the five classical moons. Umbriel has the oldest and darkest. Umbriel and the two largest, Titania and Oberon, were barely glimpsed by Voyager 2, but the four largest moons may have oceans buried beneath their icy crusts, perhaps even spewing plumes of water into space.
“Clearly, we need better coverage of these moons,” Cartwright said, noting in particular their northern hemispheres, which Voyager 2 couldn’t see at all. Also, Voyager 2 saw only one snapshot, taken while the Southern Hemisphere was in spring.
Much of the work Cartwright envisions on these worlds could be done with instruments that a Uranus orbiter would carry independently, such as its cameras. But it also encouraged mission planners to consider adding a dust analyzer that could identify compounds based on their weight as an instrument that would be especially valuable in understanding Uranus’ moons.
“We could collect material that is ejected from the surfaces of these moons, dust grains, and then sweep it with the dust analyzer and characterize the composition,” he said.
There is still time to propose instruments for the spacecraft. NASA has said it could start the first studies of what a mission could be like next year. However, Cartwright encouraged scientists not to give up.
“It’s important that we start this mission as soon as possible so that we can get the Jupiter gravity assist window, hit that window between 2030 and 2034 so that we can get to Uranus faster, before the system returns in the spring of south by 2050,” he said. said
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